The Difference in Ground Reaction Force between Two Landing Strategies of Two
Dunking Styles of Basketball Players
by
Hans P. Wulf Jr.
Submitted in Partial Fulfillment of the Requirements for the
Master of Science in Exercise Science Degree
Kinesiology Department
STATE UNIVERSITY OF NEW YORK COLLEGE AT CORTLAND
Approved:
___________
Date
_______________________________
Jeff Bauer, Ph.D.
Thesis Advisor
___________
Date
_______________________________
John Foley, Ph.D.
Thesis Committee Member
___________
Date
_______________________________
James Hokanson, Ph.D.
Thesis Committee Member
___________
Date
_______________________________
Eileen H. Gravani
Associate Dean of Professional Studies
ABSTRACT
Basketball is a sport that involves many impacts with the ground from various
jumping tasks, such a dunking a basketball, rebounding, and shooting. Repetitive impacts
with the ground have been related to many injuries that occur while playing basketball.
The purpose of this study was to quantify expected peak ground reaction forces
differences between one-footed and two footed landings when dunking a basketball.
Eight recreational, Division II and III college male players were recruited (age 22.25 ±
2.38 yrs; height 195.42 ± 4.68 cm; mass 98.55 ± 16.98 kg) for the study. The testing was
performed at the Institute for Human Performance at SUNY Upstate in Syracuse, NY.
Each participant needed to dunk three times while landing on one foot, and three more
times while landing on two feet for the one and two handed dunks. Only three
participants were able to perform a two-handed dunk, so descriptive analysis was done
for the two-handed dunk trials. For the one-handed dunk trials, the two-footed landing
strategy (M= 7.66 ± 1.57 BW) was significantly greater (p < 0.05) than the one footed
landing (M= 6.2 ± 1.18 BW) strategy for peak ground reaction force. Impulse was
significantly greater for the two-footed landing strategy (M= 719.23 ± 157.53 N∙s) when
compared to the one-footed landing strategy (M= 602.83 ± 188.6 N∙s). For the twohanded dunk trials, the two-footed landing strategy had greater peak ground reaction
forces (M= 8.98 ± 1.64 BW) and impulse (M= 927.29 ± 586.37 N∙s) than the one-footed
landing strategy peak ground reaction forces (M= 6.4 ± 1.57 BW) and impulse (M=
527.75 ± 182.62 N∙s). The greater forces and impulses produced during the two-footed
landing strategy are dispersed between both legs, which could lead to a lower
predisposition of stress related injuries in this landing strategy.
ii
ACKNOWLEGEMENTS
I would like to thank several people, without whom this project could not have
been completed.
My thesis committee: Dr. Jeff Bauer, chair, Dr. John Foley, and Dr. James
Hokanson for all of their help and support throughout this process. You always kept me
on top of the whole thesis process while making sure everything was going the way I
wanted it to.
My research assistant: D.J. Bevevino for taking time out of your busy schedule to
assist me with the data collection.
Nat Ordway, for meeting with me many times and letting me use the facilities at
the Institute for Human Performance. This study would have not have been possible if it
was not for you.
My subjects: Division II and III basketball players and recreational basketball
players, I appreciate and thank you all for traveling to the test site and volunteering your
free time in the laboratory for data collection.
I am very appreciative of everyone’s willingness to contribute their time,
expertise, and patience with me. Without the help from all of you, none of this could be
possible.
iii
TABLE OF CONTENTS
Page
Abstract ............................................................................................................................... ii
Acknowledgments.............................................................................................................. iii
Chapter
1. Introduction .....................................................................................................................1
Problem Statement ...................................................................................................2
Research Hypotheses ...............................................................................................2
Delimitations ............................................................................................................2
Limitations ...............................................................................................................3
Assumptions.............................................................................................................3
Operational Definitions ............................................................................................4
Significance of the Study .........................................................................................5
2. Review of Literature .......................................................................................................6
Physiology of Basketball .........................................................................................6
Heart rate ......................................................................................................7
Lactate ..........................................................................................................7
Nutrition .......................................................................................................8
Aerobic Capacity .........................................................................................8
Anaerobic Capacity......................................................................................9
Basketball Injuries & Rates ...................................................................................10
Ankle Injuries.............................................................................................10
Knee Injuries ..............................................................................................11
Isokinetics ..............................................................................................................11
Ground Reaction Forces ........................................................................................13
Jump Landing.........................................................................................................14
Landing Strategies & Shock Attenuation ..................................................14
Neuromuscular Recruitment ......................................................................15
Summary ................................................................................................................16
3. Research Manuscript I- Pilot Study ..............................................................................18
Introduction ............................................................................................................18
Purpose of the Study ..................................................................................18
Statement of Problem .................................................................................18
Research Hypothesis ..................................................................................19
Delimitations ..............................................................................................19
Limitations .................................................................................................19
Assumptions...............................................................................................20
Operational Definitions ..............................................................................20
Significance of the Study ...........................................................................20
Methods..................................................................................................................21
iv
Participants .................................................................................................21
Instruments .................................................................................................21
Design & Procedures .................................................................................22
Statistics .....................................................................................................23
Results ....................................................................................................................23
Participants .................................................................................................23
Vertical Jump Testing ................................................................................24
One-Handed Dunk .....................................................................................25
Two-Handed Dunk.....................................................................................26
One-Handed vs. Two-Handed Dunking ....................................................27
Discussion ..............................................................................................................28
Assumptions...............................................................................................28
Ground Reaction Force ..............................................................................29
Jump Landing.............................................................................................30
Injury ..........................................................................................................31
Additions/Further Research .......................................................................32
Conclusion .................................................................................................33
4. Research Manuscript II .................................................................................................34
Methods..................................................................................................................34
Research Assistant .....................................................................................34
Participants .................................................................................................34
Instruments .................................................................................................35
Procedures ..................................................................................................36
Statistical Analysis .....................................................................................38
Results ....................................................................................................................39
Anthropometrics ........................................................................................39
Ground Reaction Force ..............................................................................39
Impulse .......................................................................................................41
Discussion ..............................................................................................................43
Ground Reaction Forces ............................................................................43
Movements .................................................................................................44
Impulse .......................................................................................................45
Shock Attenuation ......................................................................................45
Muscle Activity & Injury ...........................................................................47
Strength Training .......................................................................................47
Summary ....................................................................................................48
Conclusions ................................................................................................49
Recommendations ......................................................................................49
References ..........................................................................................................................51
v
List of Tables
Pilot Study
Table
1
2
Title
Page
Participant Demographics ......................................................................................24
Recorded Data ........................................................................................................24
Research Study
3
Anthropometrics ....................................................................................................39
vi
List of Figures
Pilot Study
Figure
1
2
3
4
Title
Page
Average Peak GRF for Vertical Jumps ..................................................................25
Average Peak GRF for One-Handed Dunks ......................................................... 26
Average Peak GRF for Two-Handed Dunks .........................................................27
Average Peak GRF- One vs. Two Handed Dunk .................................................28
Research Study
5a
5b
6
7
8
9
10
One-Footed Dunk Landing ....................................................................................39
Two-Footed Dunk Landing....................................................................................40
One-Handed Dunking ............................................................................................40
Two-Handed Dunking ...........................................................................................41
One-Handed Dunk Impulse Averages ...................................................................42
Two-Handed Dunk Impulse Averages...................................................................42
Heel (Flat-Footed) Landing ...................................................................................46
vii
List of Appendices
Appendix
A
B
C
D
E
F
G
H
Title
Page
Informed Consent...................................................................................................56
Modified PAR-Q....................................................................................................58
Arrival Script .........................................................................................................60
Floor Layout...........................................................................................................62
Data Collection Sheet ............................................................................................63
Randomization of Landing Style Table .................................................................65
Dunking Script for Maximal Effort .......................................................................66
Procedure Matrix ...................................................................................................67
viii
CHAPTER I
INTRODUCTION
The average basketball player jumps about 70 times per game, which puts a lot of
stress upon the knee and ankle joints (Abdelkrim, Fazaa, & Ati, 2006). Jumping tasks are
the leading cause of injury among basketball players (Cumps, Verhagen, & Meeusen,
2007; Meeuwisse, Sellmar, & Hagel, 2003). McClay, Robinson, Andriacchi, Frederick,
Gross, & Martin (1994) found that while performing a lay-up, subjects produced 8.9
times their body weight when landing, which greatly stresses the ankle and knee joints
during jumping tasks.
Ankle and knee injuries are the two most common injuries among basketball
players (Cumps et al., 2007; Meeuwisse et al., 2003). McClay et. al (1994) found that the
continuous stress from all the jumping tasks performed wear down joints and tendons,
causing a high risk situation. Gray, Tauton, McKenzie, Clement, McConkley and
Davidson (1985) found that of the injured basketball players in their study, nearly 60% of
them were injured while landing from a jump and that the landing strategy most widely
used resulted in twisting the ankle upon impact to attempt to dissipate extremely high
ground reaction forces (GRF’s) in the lower extremities
Landing asymmetrically, landing on one foot before another, can result in injuries
when performing jumping tasks (Kovacs, Tihanyi, De Vita, Racz, Barrier & Hortobagyi,
1999). Basketball players perform jumping tasks to shoot, dunk, perform lay-ups,
rebound and block shots. One-footed landings result in most of the landing force being
absorbed by the initial landing foot, creating higher stress in the joint, muscle or bone of
the contact leg. Tillman, Criss, Brunt, and Hass (2004) found that female volleyball
1
players landing on one-foot produced nearly twice as much GRF (M= 3.24 times body
weight), compared to landing on two-feet (M= 1.85 times body weight) when performing
a vertical jump.
Problem Statement
The purpose of this study was to quantify expected peak GRF differences between
one-footed and two footed landings when dunking a basketball.
The independent variables were the one-handed dunk technique, and the onefooted and two-footed landing strategies. The two-handed dunk technique is the
independent variable when the subjects perform this type of dunk. The dependent
variables were the peak GRF and impulse values from each style of dunking.
Research Hypotheses
The following hypotheses were proposed prior to data collection:
1. The two footed landing strategy will generate statistically significantly lower GRF
values when compared to the one footed landing strategy.
2. Dunking with two hands will result in lower GRF’s than dunking using the one handed
technique.
Delimitations
Delimitations imposed by the researcher included selecting only male subjects,
college and recreational level basketball players, college aged athletes (18-23 years old)
and all dunks were performed with a run up parallel to the baseline.
1. The subjects for this study were confined to male subjects. Males more often meet the
physical requirements to dunk. This means that there would be no gender effect
size in the analysis.
2
2. Recreational and college basketball players were selected to participate. This
demographic was more readily available to help with conducting this study.
3. The participants’ ages ranged from 18-26 years.
4. Subjects were asked run up to dunk a basketball from a starting position parallel to the
backboard, instead of from in front of the basket like one normally would. Since a
portable basketball hoop was used, the issue of landing on the support base was
an injury concern. Dunking from the along the baseline ensured no one landed on
the base, thereby minimizing injury risk.
Limitations
Limitations of this study included a small sample size of 8 for one-handed dunks
and a sample size of 3 for the two-handed dunks.
1. Only 8 subjects could be recruited for the one-handed dunk group and, of those 8, only
3 participated in the two-handed dunk group. The sample size for the two-handed
dunk group was expected to be smaller since not all basketball players can dunk
using two hands. Dunking with one hand is an easier task, with more players
being able to perform the skill.
Assumptions
The researcher assumed that the subjects were accurate when answering questions
about previous injury, that the instruments used for data collection were valid and
reliable, and that subjects had mastered the skill of dunking a basketball with one and two
hands.
1. A Modified PAR-Q & YOU, a health questionnaire that ensures participants are
healthy enough to participate in the study, was used to insure that each subject
3
was healthy enough to participate and provided the researcher with knowledge
related to any past lower extremity injuries they might have suffered.
2. Prior to testing, the 2 Kistler Instrument Corp piezoelectric force plates model 9287B
(Amherst, New York) were calibrated to manufacturer specifications. It was
assumed that following proper calibration, the instruments reliably and accurately
recorded data.
3. The study required participants to have already mastered the skill of dunking a
basketball. Subjects were assumed to be able to perform one-handed and twohanded dunks with ease and be able to land on either one or two feet after dunking
as directed.
Operational Definitions
Force Plate- An instrument used to accurately measure ground reaction forces (GRF).
Dartfish- Biomechanical video analysis software used to analyze the motion and actions
of people captured on digital video.
Newtons- Units of force with units of kilograms · meters/seconds2
Force- An influence that causes a mass to accelerate
Dominant Leg- the leg a person would self select to to kick a ball
Ground Reaction Force- Force exerted by the ground on a body in contact with it;
measured in Newtons
Landing Strategy- The way a person lands from a jumping task; either using one or two
feet to land
One-footed Landing- Landing on one foot after a jumping task
Two-footed Landing- Landing on two feet after a jumping task
4
Isokinetics- the muscle force applied by a body segment during a movement at a constant
velocity
Stress- an internal measure of force per unit area of contact
One-handed dunk- a dunk performed with one-hand pushing the ball through the basket’s
rim
Two-handed dunk- a dunk performed with two-hands pushing the ball though the
basket’s rim
Significance of the Study
The purpose of this study was to determine which landing strategy, one-footed or
two-footed, generates lower GRF’s from dunking a basketball. A comparison of onehanded and two-handed dunking techniques was used to determine which technique
generates greater GRF when landing. Tillman et al. (2004) found in their study that
landing on one-foot (M= 3.24 times body weight) produces twice as much force as
landing on two-feet (M= 1.77 times body weight) when landing from a vertical jump.
Determining which landing strategy generates a lower GRF can help decrease the
likelihood of injury from occurring. Lower GRF may lead to decreasing the stress placed
on the joints (ankle and knee) involved in landing from jumping tasks, thereby reducing
the risk of injury (Meeuwisse et al., 2003). Since basketball is a game consisting of a lot
of jumping tasks, the overuse of these joints can take its toll on the athlete from “wear
and tear”. The less force a person generates while landing, the better. This knowledge can
help keep athletes safe and healthy in the future.
5
CHAPTER II
LITERATURE REVIEW
Even though dunking a basketball is very popular, it is not uncommon for players
to injure themselves from landing on others, landing too hard or landing improperly from
this jump task (McClay, Robinson, Andriacchi, Frederick, Gross, Martin, Valiant,
William, & Cavanagh, 1994). Knowledge of the force values from landing and the proper
way to land may help lead to a reduction in jumping related injuries. There have been
few studies that provide injury reports (Meeuwisse, Sellmer, & Hegal, 2003) and landing
force values (Gray, Tauton, McKenzie, Clement, McConkley & Davidson, 1985) from
jumping tasks. There has been little research done specifically on landing related injuries
in basketball. This chapter will address background information concerning the
physiology of playing basketball, basketball injuries and injury rates, isokinetics, ground
reaction forces and jump landing.
Physiology of Basketball
Basketball is a fast paced game with a great deal of stopping and starting, running,
and jumping. The athlete performs jumping more than any other skill in basketball,
besides running (Abdelkrim, Fazaa & Ati, 2006; Cumps, Verhagen, & Meeusen, 2007).
Between the different positions, centers are jumping the most times per game (M = 49,
SD= 3) (Abdelkrim, Fazaa & Ati, 2006). The center position is jumping, on average, once
every 0.98 minutes at the collegiate level. Repetitive jumping results in high stress in the
knee, hip and ankle joints (Abdelkrim, Fazaa & Ati, 2006). Injury occurs from high stress
activities which require the athlete to function at near maximal heart rate, just like in
basketball.
6
Heart Rate. At the collegiate level for men, the mean heart rate during a game for
all positions was found to be 171 beats/minute (b∙min-1), which equates to be 91% of the
maximal heart rate (Abdelkrim et al., 2006). Centers were found to have the lowest heart
rates because they were involved in less of the more high intensity portions of the game,
such as sprinting down the floor on a fast break and driving to the basket. The average
guard’s heart rate was 176 b∙min-1 at the collegiate level for males. Near the end of the
game, or the 2nd half at the college level, each player’s heart rate had dropped
significantly (P < 0.05) due to fatigue (Abdelkrim, Fazaa & Ati, 2006). Fifteen percent of
activity in a game was spent in high intensity activity, which is with a heart rate (HR) ≥
90% HRmax, 35% was spent standing/walking, 31% was involved in shuffling, and the
rest of the competition performed at an intensity greater than walking (McInnes, Carlson,
Jones and McKenna, 1995).
Lactate. Basketball emphasizes the use of the anaerobic energy system, so the
onset of lactate build up in the blood is to be expected. Abdelkrim et al. (2006) found that
before the game, plasma lactate concentrations were 6.05±1.27 mmol/l and only
4.94±1.46 mmol/l when the game had ended. Their study showed how the decrease in
high intensity exercise and increase in stoppage time over the course of the game led to
the increase in splanchnic blood flow, which caused an increase in the resynthesization of
glycogen by the liver (Abdelkrim et al., 2006). The resynthesis of the glycogen by the
liver shows how near the end of the game the body is supplied with more adenosine
triphosphate (ATP), or energy. This means the athlete will still be able to dunk, even after
participating in a long, strenuous game of basketball.
7
Nutrition. Maintaining proper nutrition is beneficial to athletic performance (Ziv
& Lidor, 2009). Basketball players are told they should maintain a positive energy
balance, while avoiding low-energy intakes since basketball is a very demanding sport.
For an average balanced meal, a basketball player should consume the following
macronutrients, carbohydrates (55-58% of energy), fats (25-30%), and proteins (1215%). Additional supplements to supply micronutrients will be necessary to take during
an intense basketball season (Ziv & Lidor, 2009).
Aerobic Capacity. Several studies measured VO2max between the different
positions on a basketball team and found that it ranged from 50-65 ml∙kg-1∙min-1 on
average, with guards having the higher VO2max and the centers having the lowest
(Ostojic, Mazic, & Dikic, 2006; Ziv & Liddor, 2009). In a study by Gotsentas, Landor,
and Andziulis (2004), VO2max was found to have a strong negative correlation (r= 0.83)
to the mean HR and a moderate correlation to HRmax (r= 0.699) of basketball players
during a 3.5 minute shooting drill. VO2max was found to be moderately correlated (r=
0.663) to work rate (W). Each of these correlations were found to be significant (p <
0.05).
In other studies (Gotsentas et al., 2004; Laplaud, Hug, & Menier, 2004), an
improvement in VO2max after the implementation of a new aerobic training program was
observed. There was a significant increase (P < 0.05) in the used fractions of maximal
reserve existing at rest, and an increase in VO2 and W at the instant equality of the
pulmonary gas exchange (RER= 1.00). There was a significant decrease (P < 0.05) in the
HRrest for the athletes, which signifies an improvement in the player’s aerobic capacity
from the completion of their new aerobic training program. These improvements also
8
lead to the conclusion of the ability to have a better capacity for higher exercise
intensities (Laplaud et al., 2004).
Catersiano, Patrick, Edenfield, & Batson (1997) showed in their study how
aerobic capacity decreases over the season. The players are working on their basketball
skills with small amounts of aerobic and resistance training during the year. The VO2max
of starters did not decrease, but stayed the same, and the reserve players saw a significant
(p < 0.05) drop of 5.2 ml/kg/min on average (Catersiano et al., 1997).
Anaerobic Capacity. Just like building up the aerobic capacity of a basketball
player, it is just as important to build the anaerobic capacity. Crisafulli, Melis, Tocco,
Laconi, Lai, and Cancu (2002) found that basketball players who were being analyzed
during a game that have the highest velocity, acceleration, mechanical power and
velocity endurance had the highest external mechanical work versus energy consumption
ratio. This can be concluded as those athletes with the highest biomechanical qualities,
have the highest anaerobic capacity and power. There was a significant (p< 0.05) and
strong correlation (r > 0.80) when comparing peak acceleration value, external
mechanical work and peak mechanical power to external mechanical work versus energy
consumption ratio (Crisafulli et al., 2002).
There are many biomechanical factors that lead to having a high anaerobic
capacity. Since basketball players perform around 995 movements per game (McInnes et
al., 1995), the majority of the energy consumed comes from the immediate and glycolytic
energy systems. The increase of the aerobic capacity is necessary to help the athletes
recover faster (Gocentas et al. 2004; Gocentas & Landor, 2006; Tavino, Bowers, &
9
Archer, 1995). The better and the faster the athlete recovers, the better they can perform
their basketball specific skills.
Catersiano et al. (1997) had discovered that the anaerobic capacity of basketball
players decreased significantly (p < 0.05) over the season. The bench press 1 repetition
maximum (1RM) had decreased 8-15 kg and the leg press 1RM decreased 20-35 kg. This
was found to occur because of the decrease in resistance training during the season.
Basketball Injuries & Risk
Even though basketball is considered a non-contact sport, it has higher injury
rates and risks than some contact sports such as hockey (Meeuwisse et al., 2003).
Research on injuries has mainly gone to the more popular contact sports where injuries
occur frequently, such as American football (Cumps, Verhagen, & Meeusen, 2007). The
ankle, knee and hip joints experiences strain from all the cutting, running, jumping,
standing, and crouching during a normal basketball game or practice (Cumps et al., 2007;
Meeuwissse et al., 2003). Performing these tasks frequently and at a high intensity can
lead to injury.
Ankle Injuries. One of the most common acute injuries resulting from playing
basketball is the ankle sprain (Cumps et al., 2007; Meeuwissse et al., 2003). Cumps et al.
(2007) and Meeuwisse et al. (2003) found in their studies that about 67% of all injuries,
that occurred while playing basketball, where acute injuries. About 50% of all acute
injuries were ankle injuries, thus making it the most common acute injury. According to
Cumps et al. (2007), an acute injury is defined as an injury that causes a person to miss
less than seven sessions of practices and/or games. Ankle injuries occurred 1.26 times per
every 1000 hours of exposure to play on average for men and women at professional,
10
national and regional basketball levels. During that exposure, 52.9% of injury came from
re-injuries and 47.1% came from new injuries to the ankle (Cumps et al., 2007;
Meeuwisse et al., 2003). Ankle injuries cause a loss of 5.47 days or sessions of basketball
practice/games on average (Meeuwisse et al., 2003). Both studies found that ankle
injuries are the most common injuries for basketball players. The jumping tasks are the
leading cause of ankle injury. Injury mechanisms include landing on another person’s
foot or by landing awkwardly which could cause the ankle to buckle under applied
pressure.
Knee Injuries. Knee injuries are the second most common injury in basketball
players (Cumps et al., 2007; Meeuwisse et al., 2003). Knee injuries are considered an
overuse injury, which is defined by Cumps et al. (2007) is a recovery period of more than
7 days. Cumps et al. (2007) and Meeuwisse et al. (2003) established that there were, on
average, 35.5% of the overuse injuries were knee injuries. Eighty percent of knee pain
was defined as jumper’s knee caused by repetitive and continuous jumping during shots,
rebounds, lay ups and dunks (Cumps et al., 2007). Centers are usually located in the area
right around the basket, where it is very crowded because players are trying to retrieve
rebounds from a missed shot. The two basketball positions that jump the most are the
centers and forwards, and these two positions are the positions that like to dunk the most.
Therefore, these players are always at risk for injury by landing wrong on someone’s
foot, landing improperly or just by landing with too much force.
Isokinetics
Isokinetics is the muscle force applied by a limb during a movement at a constant
velocity (Theoharopoulos & Tsitskaris, 2000). The isokinetic profiles of an athlete can
11
help inform the coaches of the athlete’s potential physical abilities. Isokinetics may be
measured through various testing, such as using an ergogenic bike. The various skills
associated with basketball causes the athletes to develop a dominant limb, which is
defined by the researchers as the limb used to jump off of, kick a ball with and start
running (Schiltz, Lehance, Maquet, Bury, Crielaard & Croisier, 2009). Theoharopoulos
and Tsitskaris (2000) found that on an ergogenic bike, there were no significant
differences between dominant and non-dominant plantar and dorsiflexion ankle muscle
strength (tibialis anterior, soleus, and gastrocnemius) of professional basketball players.
A balance in strength between these muscles on both ankles is a great way help prevent
injury (Theoharopoulos & Tsitskaris, 2000). When jumping, the plantar and dorsiflexion
muscles can support the addition of added stress to the ankle joint, so the ankle can stay
stable (Theoharopoulos & Tsitskaris, 2000).
Knee isokinetics plays another important role in injury prevention among
basketball players (Schiltz et al., 2009). Schiltz et al. (2009) found that the professional
players had a higher absolute peak torque value than the junior level and the recreational
level groups in both their flexor and extensor muscles. Athletes with a history of injury to
the knee were found to not perform as well as those who did not have previous injuries
(Schiltz et al., 2009; Theoharopoulos & Tsitskaris, 2000).
Overall strength in the knee is very important. As a basketball player, strength is
very important to jump for rebounds, performing a lay-up or dunk, and for running. The
more strength there is in the muscles of the lower extremities and the muscles
surrounding the knee and ankle joints (tibialis anterior, gastrocnemius, soleus, etc.), the
lower the injury risk to these joints (Schiltz et al., 2009).
12
Ground Reaction Forces
Many forces are absorbed by an athlete’s body upon landing from different
jumping tasks, such as dunking, performing a lay-up and jumping for a rebound. Ground
reaction forces are a good indicator to the intensity and stress the body encounters during
contact with the ground from a jump landing or just simply running (McClay et al.,
1994). Gray, Tauton, McKenzie, Clement, McConkley and Davidson (1985) reported that
nearly 60% of the 76 female basketball players surveyed were injured from jumping
tasks. While attempting to dissipate the extremely high ground reaction forces in the
lower extremities caused by landing from a jump, many of these females were injured
after landing improperly causing them to sprain their ankles. Tillman, Criss, Brunt, and
Hass (2004) found that when comparing single-footed landings to two-footed landings
from a vertical jump, single footed landings produced almost twice as much peak loading
force (3.23 times body weight) than the two-foot landings (1.86 times body weight). In
single-foot landings, EMG values increased in muscle activity from 28% to 72% to show
how much more work the muscles must do when both legs are not involved to help
absorb the GRF (Tillman et al., 2004).
McClay et al. (1994) studied the biomechanics of several basketball maneuvers:
running, starting, cutting, stopping, jump shot takeoff, jump shot landing, layup takeoff,
layup landing, vertical jump takeoff, vertical jump landing and shuffling of professional
players. The investigators found that the layup landing created the most vertical ground
reaction force (up to 8.9 times body weight). The next closest was the jump shot landing,
which only produced 6.0 times body weight. Gymnasts landing from a somersault ranged
from 6.0-7.0 times body weight, while basketball jump landings ranged from 4.3-8.9
13
times body weight. Caulfield & Garrett (2004) found that athletes with a history of
previous injuries in the ankle, produced a slightly higher vertical mean magnitude of peak
GRF’s (501.9 N) than a control group (476.9 N). These landing forces can be very high,
and an athlete needs to know what his or her body if capable of to make sure their injury
risk is as low as possible.
Jump Landing
The most common mechanism of injury in basketball is asymmetric landing from
a jumping task (Kovacs, Tihanyi, De Vita, Racz, Barrier & Hortobagyi, 1999). A
basketball player can produce up to 8.9 times their body weight in ground reaction forces
when landing after performing a simple layup, which means that the lower extremities are
placed under a lot of biomechanical stress (McClay et al., 1994). A way to prevent from
injuring one’s self during jump landing tasks in basketball is to land on the forefoot
instead of the heel of the foot (Gross & Nelson, 1988). Landing on the forefoot reduces
exposure to skeletal transients by 50% when compared to landing on the heel because of
the body using its own shock attenuation, which is the soft tissues, bones, and cartilage
(Gross and Nelson, 1988).
Landing Strategies & Shock Attenuation. The body has its shock attenuation
within its bones, cartilage and soft tissue (McClay et al., 1994). Gross and Nelson (1988)
found that heel contact had less range of motion in the ankle compared to those who had
only forefoot contact. A decrease in the range of motion of the ankle joint can bring about
heel contact, which has two peak forces during landing, thus increasing the risk of injury.
Two peak GRF’s result from the forefoot striking the landing surface first, then the heel
striking the ground right afterwards. Subjects, who used their forefoot only to land,
14
greatly reduced the magnitude of force from five times their bodyweight to two times
their bodyweight, resulting in less strain and less force upon the lower limbs (Gross &
Nelson, 1988).
Different basketball skills vary in the amount of ground reaction force created and
absorbed by the athlete (Valiant & Cavanagh, 1987). The force and pressure patterns
underneath the foot during a landing phase from a vertical jump was 2.5 times the
participant’s body weight (Valiant & Cavanagh, 1987). When landing on the foot occurs
beneath the middle of the calcaneus, simultaneous ground reaction forces that equated up
to 4 times the person’s body weight were produced. When landing flat footed, ground
reaction forces were up to 6 times the athlete’s body weight (Valiant & Cavanagh, 1987).
Landing on the forefoot instead of the heel helps the body absorb less force which results
in less stress applied to the lower extremities.
Neuromuscular Recruitment. Many muscles are recruited to perform and
complete a jump landing task, including the quadriceps, hamstring, gastrocnemius,
soleus, and tibialis anterior. Before landing, people often anticipate how they are going to
land and get set for the landing to make sure they do not injure themselves. McKinley
and Pedotti (1992) found that the muscle activity starts at the ankle muscles when about
to land from a jumping task. Muscle activity then works its way up to the knee, and lastly
the hip. Before the impact of landing, the EMG activity increase dramatically. For soft
surfaces, the impact force will also be absorbed by the ground and not as much force will
be passed to whoever is landing so the muscles are relaxed (McKinley & Pedotti, 1992).
Fu and Hui-Chan (2007) found that in people with functional instability, muscles were
activated significantly sooner than the muscles of those with healthy ankles. Caulifield,
15
Crammond, O’Sullivan, Reynolds and Ward (2004) found that the peroneus longus
muscle had a significantly lower EMG score than those with healthy ankles. The
peroneus longus muscle activity controls the degrees of eversion of the ankle joint and
the less movement eversion, the higher the risk of injury.
Bisseling, Hof, Bredeweg, Zwerver, and Mulder (2008) found that the first impact
of landing is the most crucial. When a Participant has a smaller flexion in the ankle joint
during the first part of the landing phase, and a higher rate of knee movement during the
eccentric phases, it can lead to the development of patellar tendinopathy (Bisseling et al.,
2008). The ankle joint should not be stiff when landing so that the person can give some
movement to the joint as they are landing. This will prevent the absorbed force from
placing all the stress on the knee joints.
Different directions from jump landing tasks influence dynamic postural control.
Wikstrom, Tillman, Schenker, and Borsa (2008) found that when diagonal and lateral
jumps were attempted, the direction of jump will affect a person’s dynamic postural
stability, which is their ability to stay balanced while performing a movement. The more
direct forward the jump, the better stability there will be when landing. The more lateral
the jump, the less stable the landing. When performing a dunk in basketball, it is always
best to dunk straight ahead instead of from the side. This would result in the most stable
landing possible, and is the best strategy to use to prevent injury.
Summary
Knee and ankle injuries are likely to occur when landing from a jumping task
such as dunking. Knowing how to land without placing all the absorbed force in one area
can keep athletes healthy. Improper takeoff and/or landing of jumping tasks are the
16
leading cause of knee and ankle injuries in basketball (Cumps et al., 2007; Meeuwisse et
al., 2003). Different landing strategies will play a role in understanding injury prevention
from the effects of single or two footed landings to where on the foot the athlete is
landing (Mclay et al., 1994; Valiant & Cavanagh, 1987). Injury may happen to a
basketball player no matter how hard they try and prevent it, but the injury severity may
be reduced by using proper landing mechanics.
17
CHAPTER III- RESEARCH MANUSCRIPT I:
PILOT STUDY
INTRODUCTION
There has been little research done on basketball injuries since it is considered a
non-contact sport. However, compared to combative sports such as American Football,
there have been some studies on the injury rate of basketball players and they have
identified jumping tasks as the leading cause of injury to players (Cumps et al., 2007).
Landing on top of another player’s foot and landing on one foot are the two leading
causes of these injuries (Cumps et al., 2007). Ankle injuries are the most common
injuries in basketball. When landing from jumping tasks, the lower extremities absorb a
greater amount of GRF than from running.
McClay et al. (1994) tested several basketball skills and their GRF values. The
skill producing the highest amount of ground reaction force was the landing phase of a
layup (dunking was not performed in this study), where the Participants produced 8.9
times their body weight on average (McClay et al., 1994). McClay helps give an insight
on how much force is expected to be produced when landing from a jumping task in
basketball that involves the athlete to quickly jump towards the rim.
Purpose of the Study
The goal of this study was to determine which type of dunk, one-handed or twohanded, would result in greater landing GRF.
Statement of Problem
Different landing strategies result in varying levels of landing force. The greater
the landing force, the greater the likelihood of injury.
18
Research Hypothesis
There will be a greater landing GRF following a one-handed dunk technique than
in a two-handed dunk technique.
Null Hypothesis
There will be a greater landing GRF following a two-handed dunk technique than
in an one-handed dunk technique.
Delimitations
This study was delimited to only recreational basketball players, participant’s age
ranged from 20-22, and only male subjects.
1. Only recreational basketball players were available for the study. No collegiate
basketball players were available to participate.
2. The participant’s ages ranged from 20-22. No one older than a college age range was
available to participate in the study.
3. Only male subjects volunteered, and met the physical requirements for the study. No
females responded or were able to dunk.
Limitations
This study had a limited number of participants used, and no force plates were
available to record landing GRF.
1. Only five volunteers met the study requirements.
2. Proper force plates were not available for use for the dunk trials of this study. A force
plate was available to use for the vertical jump trials. Forces were calculated using
time of shock absorption, velocity final and work for the dunk trials.
19
Assumptions
Assumptions of this study were that the participants had mastered the skill of
dunking a basketball one-handed and two-handed, and the dunks were performed with
maximal effort.
1. The participants have mastered the skill of dunking a basketball and should be able to
perform the dunks with ease.
2. Participants dunked with maximal effort. They were asked to make a maximal effort,
but there was no way to determine if they did.
Operational Definitions
Force Plate- an instrument used to measure ground reaction forces
Dartfish- a biomechanical video analysis software used to analyze the motion and
action of people captured on digital video.
Newtons- are units of force measured in kilograms · meters/seconds2, which is
based on mass multiplied by acceleration
Force- is whatever causes an object with a mass to accelerate
Dominant Leg- the leg you would use to kick a ball with
Ground Reaction Force- any force exerted on the ground by contact with the body
Landing Strategy- the way a person lands from a jumping task
Significance of the Study
The purpose of the pilot study is to determine which dunk, one-handed or twohanded, produces more force when landing. Determining which style of dunking
produces more landing force can be useful for athletes to help prevent injury. In the study
by Tillman (2004), it was shown that landing from vertical jumps on one foot produced
20
twice as much force, on average, as landing on two feet, which indicates that landing on
two feet can lead to a lower likelihood of injury (Tillman et al., 2004). Determining what
style of dunking produces a greater landing GRF, can help athletes reduce the likelihood.
METHODS
Participants
Three male SUNY Cortland students, ranging in the age from to 20-22 years,
volunteered for this study. Each volunteer had previous experience playing basketball and
had the ability to dunk a basketball on a standard ten foot high rim. Participants were
asked to read and sign an informed consent before the study to know the risks associated
with participation. Numbers were assigned to the participants to keep their names and
information anonymous. Each participant read and signed an informed consent
(Appendix A) form indicating that they knew of the risks present in the study.
Instruments
The participants’ height and weight were measured on a scale (Detecto Medic)
prior to testing. A Bertec force plate (Columbus, Ohio), which is used to measure force in
Newtons. Reliability and validity of the force plates have been proven to be accurate and
correct (Whittle, 1997). The force plate was linked to a computer that used Peak Motus
System version 6.0 software. A JVC digital camcorder was used to record digital videos
of the vertical jumps and the dunks. The camera was linked to a computer using the
Dartfish 4.5 software, which was used to measure time of the flight from take-off to
landing, and distance traveled while jumping.
21
Design & Procedures
Three male recreational basketball players at SUNY Cortland volunteered to
participate in the study. They ranged in the ages from 20-22. All participants play the
forward position when they participate in the game of basketball.
The participants were tested during a single experimental session where their max
vertical jump height was measured, followed by their execution of a series of three onehanded dunks and three two-handed dunks, which were filmed using the JVC digital
camcorder recording at 30 Hz. Upon arrival for testing, the participants had their height
(centimeters) and weight (kilograms) recorded. Each participant’s max vertical jump was
measured using a Vertec Vertical Jump Tester (Owatonna, MN). Each participant stood
on the Bertec force plate and performed a counter movement vertical jump. The height of
the jump and the landing GRF were measured. A JVC camcorder recorded a digital video
of each participant jumping. The videos were then uploaded into Dartfish software for
analysis. A meter stick was placed in the field of view, along the primary plane of
motion, and was used to calculate real world distance values from the video information.
The three vertical jump test scores and the average peak landing GRF’s were used for
further analysis later in the study.
Next, the participants performed the required dunks. Each participant dunked a
basketball with one hand three times and then three more times with two hands. They
were given a 10 minute warm up period to stretch and practice dunking. Each participant
started their approach to the basket from the midway point between the foul line and
three point line on the basketball court. The participants were asked to follow a specific
path to the basket while dunking the basketball for the best video results. A JVC
22
camcorder recorded each dunk trial directly linked to a computer through the use of
Dartfish software. A meter stick was aligned to the plane of motion as a reference point
for distance. Time of flight, distance, and take-off/landing velocities was found using the
Dartfish software. The videos were used for further analysis to determine the landing
force of the participant. The average ground reaction force from the one and two handed
dunk trials from each participant were calculated using the following equation:
Average Reaction force = [(velocity final – velocity final)/ ∆ time of shock
absorption] x Work
The results from the above equation were then doubled to find the peak landing
force of the participant. Data was then normalized to represent how much force was
generated based on the participant’s body weight.
Statistics
A statistical analysis was not run because the sample size was too small. A
descriptive analysis was done instead.
RESULTS
Participants
The study began with five participants. Three dropped out of the study, two due to
personal reasons and the third as the result of injury. The injured participant was able to
complete the vertical jump testing session, but was not able to participate in the dunking
session of the study. The participant had sprained his ankle while landing on top of
another person’s foot after attempting to dunk a basketball. He was using a one-footed
landing strategy. Two subjects completed all the phases of the study. Table 1 illustrates
23
the anthropometrics of the participants, and table 2 shows the results of each participant
from the vertical jump and the dunk trials.
Participant Number
Height (cm)
Weight (kg)
Playing Position
1
196.9
82.3
Center/Forward
2
190.5
100.65
Center/Forward
3
198.1
100.5
Forward
Averages
195.2
94.5
Table 1. This table shows the participant’s anthropometrics for the study.
1
Vertical
Jump Height
(cm)
49.5
Average Peak
Vertical Jump
GRF (BW)
3.94
Average Peak
One-Handed
Dunk GRF (BW)
6.25
Average Peak
Two-Handed
Dunk GRF (BW)
6.47
2
39.4
4.02
7.95
3.74
3
49.5
3.12
N/A
N/A
Average
46.1
3.69
7.1
5.11
Participant
Number
Table 2. This table shows the average peak scores to the vertical jump test, and the
average peak landing GRF the one-handed and two handed dunks based on body weight
(BW).
Vertical Jump Testing
Participants tested their vertical jump using the Vertec Vertical Jump Tester.
Participants 1 and 3 had the highest vertical jump height with 49.5 cm. Participant 2 only
had a vertical jump height of 39.4 cm. Dartfish video analysis software was used to time
each participant’s jump. Participant 3’s average flight time for his vertical jump trials was
the longest (M = 0.633 seconds (s)). Participant 1 was in the air the next longest (M = 0.6
s) and participant 2 was in the air the shortest (M = 0.55 s). Participant 2 had the smallest
average score for the vertical jump (M= 39.4 cm) and the shortest flight time (M=0.55 s).
24
The vertical jump landing force varied for each participant. Participant 2 produced the
highest landing GRF, which was 4.02 times body weight (BW). Participant 3 produced
3.12 BW, and participant 1 produced 3.94 BW. The average landing GRF for the vertical
jump test was 3.69 BW. Figure 1 illustrates the average peak landing GRF’s of each
participant for the vertical jump test.
Average Peak GRF for Vertical Jumps
4.5
4
3.5
GRF (BW)
3
Participant 1
2.5
Participant 2
2
Participant 3
1.5
1
0.5
0
Figure 1. Average landing GRF generated from performing the vertical jump test.
Participant 2 had an average peak GRF of 4.02 BW, 3.94 BW peak average for
participant 3, and 3.12 BW peak average for participant 1.
One-Handed Dunk
For the landing force of the one-handed dunk, Dartfish video analysis software
was used to record time and flight distances for calculating landing GRF. A difference
was found between the average peak GRF’s of participant 1 (M= 6.25 BW) and
participant 2 (M = 7.95 BW). Participant 2 produced 1.7 BW more peak landing force, on
average, than participant 1 did for one-handed dunks. Figure 2 illustrates the average
25
peak landing GRF, normalized to body weight, between the remaining two participants
for the one-handed dunk.
Average Peak GRF for One-Handed Dunks
9
8
7
GRF (BW)
6
5
Participant 1
4
Participant 2
3
2
1
0
Figure 2. Average peak landing GRF of the one-handed dunk trials. Participant 2
produced a greater landing GRF than participant 1. Participant 2 produced 7.95 BW, and
participant 1 produced 6.25 BW.
Two-Handed Dunk
Dartfish video analysis software was used to measure time and flight distance for
calculations. There was a difference found in the average landing GRF’s between
participant 1 (M = 5226.9 N) and participant 2 (M = 3690.9 N). Even though there was no
significant difference, participant one produced 1536 N, which is 70.6%, more than
participant two in landing force. Participant 1 produced an average peak landing GRF of
6.47 BW, and participant 2 produced an average peak landing GRF of 3.74 BW. Figure 3
illustrates the average peak landing GRF, normalized to body weight, of the two-handed
dunk for both participants.
26
Average Peak GRF for Two-Handed Dunks
7
6
GRF (BW)
5
4
Participant 1
Participant 2
3
2
1
0
Figure 3. Average peak landing GRF, normalized to body weight, between the two
Participants in the two-handed dunk. Participant 1 generated an average peak GRF of
6.47 BW, and Participant 2 produced an average peak GRF of 3.74 BW.
One-Handed vs. Two-Handed Dunking
Comparison of each participant’s one-handed dunks to their two-handed dunks
was then performed. The average peak landing GRF produced from the one-handed dunk
was 6.96 BW and 4.81 BW for the two-handed dunk. The average peak landing GRF of
the one-handed dunk produced 2.15 BW more, on average, than for the two-handed dunk.
Figure 4 illustrates the difference in average peak landing GRF between the two dunking
styles of all participants.
27
Average Peak GRF-One vs. Two Handed Dunk
8
7
6
GRF (BW)
5
One-Handed Dunks
4
Two-Handed Dunks
3
2
1
0
Figure 4. Average peak GRF, by body weight, of the one and two-handed dunks. The
one-handed dunk produced the highest average GRF, which was 6.96 BW. The twohanded dunks produced an average peak GRF of 4.81 BW.
DISCUSSION
From the results of the pilot study, there was a marked difference between the
landing forces of the one-handed and two-handed dunks. The one-handed dunk technique
produced a much higher peak landing GRF than the two-handed dunk technique, as stated
in the hypothesis. There were several interesting results and findings during the study.
Assumptions
In the study, assumptions were made about how the participants had a full
mastery of dunking with one and two hands, and that they would perform the task with
maximal effort. The assumption on maximal effort was not met by one participant.
Participant 1 gave a sub-maximal effort when performing the one-handed dunks, but a
maximal effort when performing the two-handed dunks. This was shown through the
28
slow approach to the basketball hoop seen in the videos. His lack of effort to the onehanded dunks is believed to be the reason why the data and results were skewed. He
would have produced more landing more if he had given maximal effort instead of only
producing an average peak landing GRF of 6.25 BW, while participant 2 produced an
average peak landing GRF of 7.95 BW.
The assumption of having a mastery of performing both dunking styles was not
met for participant 2. His attempts at the two-handed dunks were below par. He was very
hesitant and slow when attempting to dunk. The videos showed stutter steps before
jumping, which made him seem awkward in his attempts. Only one of the three dunks
was made while the other two bounced off the rim. Participant 1 demonstrated a mastery
of both dunking styles.
Ground Reaction Force
The one-handed dunk trials (M= 7.1 BW) produced a greater average peak
landing GRF compared to the two-handed dunk trials (M= 5.11 BW). It was found that
the amount of force produced ranged from 3.74-7.95 BW. McClay et al. (1994) found
that a layup landing produced 4-8.9 BW, which is very close to what was found in this
study, thus, showing how McClay’s findings could be replicated.
Gray et al. (1985) found that 60% of injuries in basketball occur from improper
landings from jumping tasks. Participant 3 agreed to let me talk about his injury in this
research brief. He was playing basketball and landed on his foot wrong when coming
down from a dunk. He landed on one foot and sprained his ankle. This injury relates to
how the force absorbed by one leg is twice as much as when landing on both legs, thus
increasing the likelihood of injury to the single leg (Tillman et al., 2004). In the study, the
29
one-footed landings (M = 7.1 BW) produced 72 % more force than the two-footed
landings (M = 5.11 BW). This study showed that the force absorbed in one-foot landings
was almost twice as much as in the two-foot landings. The athletes in this study showed
that the injury rate also increases, thus showing why the ankle and knee injury rates are
so high in basketball.
Participant 3 now has functional instability in his ankle, which is a tendency of
the foot to repeatedly give away or sprain as a result as an inability to maintain stability
of the ankle joint during activity. Players with functional instability from sprained ankles
were found to land with the same amount of GRF, and usually do not take any
precautions when landing to prevent the injury from happening again (Caulfield &
Garrett, 2004). When performing similar jumping tasks in the study, the ankle sustained
similar GRF and did not get re-injured. This was even though strength in the ankle is
reduced each time from injury. Participant 3 has to watch how he comes down when
landing and fix his old habit to prevent too much force from being absorbed by one leg.
Jump Landing
Mckinley and Pedotti (1992) found in their study that each person likes to land a
certain way. This is based on the firing of motor neurons in the muscles for muscle
recruitment. Each person learns how to land a different way, so if they land a certain way
repeatedly, the muscles will start to remember (muscle memory) what to do each time
with minimal effort (Mckinley & Pedotti, 1992). From the video, participant 1 landed
with more confidence and balance without having to try and adjust his legs in a proper
manner. Participant 2 was unbalanced and uncoordinated at times while landing. It was
30
reported in a study by Kovacs and colleagues that asymmetric landings are the leading
cause of injury in volleyball players (Kovacs et al., 1999).
Participant 2 was found to be switching legs when landing in the videos. He
would use his left leg half the time to land and his right leg to land the other half. This
participant appeared to have no dominant landing leg. In a study by Schiltz, Lehance,
Maquet, Bury, Crielaard, and Croisier (2009), it was found that the players showed no
signs of a leg dominance at both the professional and junior basketball levels. The
dominant leg is defined as which leg they use to kick a ball with. Both groups had found
to show no significance (p > 0.05) when testing both legs in a series isokinetic tests, such
as testing strength of the knee flexors and extensors. The quadricep and hamstring were
tested at 60̊ ∙s-1 and 240̊ ∙s-1 for concentric movements, and then again for eccentric
movements at 30̊ ∙s-1 and 120̊ ∙s-1. Schiltz et al. (2009) showed that there is no real
dominant landing leg in basketball players, and that they need to use both legs to be
successful. Theoharopoulos and Tsitskaris (2000) found the same results as Schiltz’s
study. They found no difference in power/torque between the defined dominant and nondominant legs. Participant 2 in this study demonstrated a sign of a dominant leg (right
leg) when landing.
Injury
The ankle injury that occurred to participant 3 is very common among basketball
players (Meeuwisse et al., 2003; Cumps et al., 2007) Meeuwisse et al. (2003) did a
survey of injuries over two seasons in a basketball league in Canada. It involved eight
men’s college level teams. Ankle injuries were found to be the most common injury,
followed by knee injuries. These injuries occurred most frequently when landing from a
31
jumping task. Meeuwisse et al.’s (2003) study had ankle injuries occurring 1.01 times out
of every 1000 hours of exposure to playing basketball.
Tillman et al. (2004) found in a study that in single-foot landings, EMG values
increased in muscle activity by 28-72% higher. The vastus medialis activity was 39%
higher in the dominant limb when comparing single-foot to two-foot landings. Hamstring
activity was 70% higher in the dominant one-foot landing than in the non-dominant twofoot landing. This shows how a jump landing on one foot is more likely to lead to injury
because of the strain in activity it puts on the muscles of the lower extremities. This could
be part of the explanation of why Participant 3 was hurt playing basketball with some
friends.
Additions/Further Research
This study was done with a limited amount of resources and participants. In the
future, this study would have a higher statistical power and be more convincing if there
were at least 10 participants. Also, the study should have been done with force plates that
were big enough for the participants to land on. The force plates used when testing
vertical jump reach height were barely big enough to fit the feet of these participants.
Force plates that were placed in a more natural setting, such as being flush with the floor
on a basketball court, would have been more effective. Testing in game situations would
be a more effective way to measure peak landing GRF because it is hard to get motivated
to perform at maximal effort in a laboratory setting. Since calculations were done, human
error could be a factor in the skewing of results. If the peak GRF was just read off a
computer screen for the dunk trials from software calculations, there is a chance for less
error to occur.
32
Conclusion
One-handed dunking (M= 7.1 BW) produced a greater average peak landing GRF
than two-handed dunking (M= 5.11 BW). The difference was quite high between the two
participants (1.99 BW). This may be due to the fact the when a person dunks onehanded, they are usually approaching the basket from further out on the court and with a
higher velocity, than those who dunk with two hands. With the amount of body weight
found from average peak landing GRF in this study (3.74-7.95 BW), it could be easily
related to McClay et al.’s (1994) study when performing a layup (4-8.9 BW). Knowledge
of what dunking style produces less average peak landing GRF can help basketball
players make the right decision. The right decision could help lead to reducing the
likelihood of injury.
33
CHAPTER IV- RESEARCH MANUSCRIPT II:
The Difference in Ground Reaction Force between Two Landing Strategies of Two
Dunking Styles of Basketball Players
METHODS
Jumping tasks are a regular part of the game of basketball. There have been
studies that have reported injury rate, basketball physiology, and the GRF of some
basketball skills. Tillman et al. (2004) found in collegiate female volleyball players that
the force produced when landing one-footed is twice the amount when compared to
landing two-footed. Meeuwisse et al. (2003) found that the most common injury suffered
by basketball players was an ankle injury, resulting from landing on an opponent’s foot
or from improper landing techniques. This chapter discusses the research assistants,
subjects, instruments, location, procedures and statistical analysis associated with this
study.
Research Assistant
One research assistant was used to help the researcher during this study. The
assistant is enrolled in the Master’s level Exercise Science program at SUNY Cortland.
The research assistant was responsible for recording anthropometry of each participant
and recording the peak GRF’s of each dunk trial.
Participants
The eight participants that volunteered to be in this study included four
recreational basketball players, three members of SUNY Cortland’s varsity basketball
team, and one member of the LeMoyne varsity basketball team. The number of
participants in this study was lower than those of similar research studies cited in the
34
literature review. Only one other study that had researched basketball movements used
similar methods.
At a minimum, subjects were able to perform a one-handed dunking skill to be
considered for participation in the study. Not all study subjects were able to perform a
two handed dunk, but those who could were instructed to do so. Participants were asked
to read and sign an informed consent (see Appendix A) before the study so they knew the
purpose of the study, the risks involved, and the testing procedures. A Modified Par-Q &
You (see Appendix B) helped to determine any conditions preventing safe participation.
Subjects who were healthy enough to perform the dunking task were chosen to
participate in the study. Approval granted by SUNY Cortland’s Institutional Review
Board was required before data collection began.
Instruments
The subjects’ weight was measured using a Pelouze model 4040 Digital scale
(Bridgeview, IL) and their height was measured, using a tape measure taped to a wall, by
the researcher prior to the start of testing. Two Kistler Instrument Corp piezoelectric
force plates model 9287B (Amherst, New York) were placed next to one another. The
force plates were arranged in a nine plate grid (seven plates were inactive), which were
flush with the floor, and were used to measure the basketball player’s peak GRF’s in
Newtons, using BioWare 3.0 software by Kistler. Collection frequency was set at 100 Hz.
A JVC digital camcorder was used to record videos of the dunking trials. The videos
were uploaded to a computer using the Dartfish TeamPro 5.5 software. Digital videos of
each dunk trial were recorded for reference and record. The force plates are calibrated
35
and automatically calibrate after each trial and have a measuring resolution of +/- 2.5 N
for a peak measurement of 10,000 N.
Procedures
For those who responded to the flyer handed out by the test administrator, a
Modified PAR Q & YOU and Informed Consent forms was handed out at a meeting prior
to the study to go over the purpose and procedures of the study. The volunteers were
asked to fill out the Modified PAR Q & YOU form as accurately as possible. If the
volunteer was not healthy enough to participate, they were excluded from participation in
the study. The study required volunteers to be healthy enough to meet the physical
demands of dunking a basketball. The modified PAR-Q and YOU was administered
before testing to ensure no one traveled all the way to the test site only to be prohibited
from participating in the study.
This study required several days of data collection. The same procedures were
followed each day of data collection. All subjects were assigned a number based on order
of arrival for confidentiality and for randomization purposes. Subjects were instructed to
wear appropriate clothing for playing basketball (i.e. basketball sneakers, shorts and a tshirt). Other clothing pieces that would not alter the dunking skill or reduce the visibility
of necessary body landmarks, such as a head band or wrist band, and any braces were
allowed.
Upon arrival at the Institute of Human Performance (IHP) on the SUNY Upstate
Medical University campus, the participants were read a script (Appendix C) of what was
to be done during that session of data collection. Next, they had their height (cm) and
weight (kg) recorded. Floor layout of the study at the IHP is shown in Appendix D. After
36
the anthropometric measurements were recorded for each subject, the subjects were asked
to warm-up for a period of ten minutes. During the warm-up period, they were allowed to
perform a dynamic warm-up for 5 minutes and to shoot around the basketball for the
other 5 minutes.
After the warm-up period was over for the subjects, each participant started their
dunk trial from the three point line marker located foul line extended on the basketball
court. Subjects were dunking the basketball from the side of the basketball hoop, parallel
to the backboard. Since the basketball hoop that was used was portable, there was an
issue of people landing on the support base which could have caused subjects to alter
their landing style. To keep the subjects from altering the landing style, they performed
the dunks from the side of the basketball hoop. The landing peak GRF was recorded on a
computer using the BioWare 3.0 software. All force plate data collected was normalized
to each person’s body weight. The weight in Newtons of each participant was found as
follows: Subject’s Weight (kg) x 9.81 m/s2. A 30 Hz JVC camcorder was set up
perpendicular to the baseline of the basketball court providing a sagittal view of the
motion for the best video results.
Subjects were randomized as to which landing style they performed first for the
one and two-handed dunks based on their order of arrival (Appendix F). Each subject
performed six dunks. Prior to each dunk trial, subjects were read another script
(Appendix G) to attempt to get maximal effort from each participant. First, they were
asked to perform three one-handed dunks landing on two feet and then followed by three
dunks landing on one foot. Participants were asked to not hang on the rim after dunking
because hanging on the rim would slow down the participant’s decent, and skew the data.
37
The sequence of three dunks landing on two feet followed by three dunks landing on one
foot was repeated for those who could perform a quality two-handed dunk. A quality
two-handed dunk was defined as a dunk that could be successfully performed as well as
the person’s one-handed dunk. The ball must go through the hoop, the approach should
be smooth with no hesitation and they must be able to repeat the two-handed dunk six
more times. Data from the three dunks of each dunk style and landing strategy were
averaged together for analysis purposes. Any of the dunk trials that did not meet the
quality standards for dunking were discarded. The above procedures are shown in a
matrix in Appendix H.
A 30 Hz JVC digital camcorder was used to video record each dunk trial. The
digital video was uploaded to a computer using Dartfish TeamPro 5.5 software. Videos
were kept in Dartfish to be used for reference.
Statistical Analysis
Statistical analysis was done using the SPSS software for Windows (Version 18).
The Kolmogrov –Smirnov test, along with skewness and kurtosis were tested to check for
normal distribution within the data in the peak GRF and impulse data. A Repeated
Measures ANOVA compared the different landing strategies of the one handed dunk
trials. A P-value less than 0.05 was considered statistically significant for all tests run.
Since there were only three participants for the two hand dunk trials, a descriptive
analysis was done for their GRF and impulse data. All graphs were made using Microsoft
Excel 2007.
38
RESULTS
Anthropometrics
The anthropometrics measurements of the participants are illustrated in Table 3.
Table 3 Anthropometrics
Subject #
1
2
3
4
5
6
7
8
AVG
St. Dev.
Age (yrs)
24
22
18
23
23
21
26
21
22.25
2.38
Height (cm)
190.50
198.12
194.31
186.69
198.12
200.66
196.85
198.12
195.42
4.68
Weight (kg)
81.00
118.00
96.60
77.00
98.00
123.40
86.20
108.20
98.55
16.98
Position
Guard
Power Forward
Small Forward
Guard
Center
Center
Forward/Center
Forward
Table 3. This table shows the descriptive statistics of the measured anthropometrics
of each participant.
Ground Reaction Force
Illustrated in Figures 5a and 5b are examples of the vertical components of the
GRF from the two landing strategies.
7000
6000
5000
4000
3000
2000
1000
0
1.99
2
2.01
2.02
2.03
2.04
2.05
2.06
2.07
2.08
2.09
2.1
2.11
2.12
2.13
2.14
2.15
2.16
2.17
2.18
2.19
2.2
2.21
2.22
2.23
2.24
2.25
2.26
2.27
Ground Reaction Force (N)
One-Footed Dunk Landing
Time (s)
Figure 5a. This is an example of GRF’s representative of one-footed dunk landing.
39
Ground Reaction Force (N)
Two-Footed Dunk Landing
4500
4000
3500
3000
2500
2000
1500
1000
500
0
Force
Plate #1
Force
Plate #2
Time (s)
Figure 5b. This is an example of GRF’s representative of two-handed dunk landings.
There was a significant difference between the two landing strategies (F(1,7)= 18.956, p <
0.01, η2= .73). The mean peak GRF for the two-footed landing strategy (7.66 ± 1.57 BW)
was significantly higher than the mean peak GRF of the one-footed landing strategy (6.2
± 1.18 BW), as demonstrated in Figure 6.
One-Handed Dunking
*
10.0
Peak GRF's (Based on BW)
9.0
*
8.0
7.0
6.0
One-Footed Landing Strategy
5.0
Two-Footed Landing Strategy
4.0
3.0
2.0
1.0
0.0
Figure 6. This is a graph comparing the one-handed peak GRF values of the one-footed
and two-footed landing strategies. There is a significant difference (p < 0.05) between the
average one-footed landing peak GRF and the average two-footed landing peak GRF.
40
The two-footed landing strategy (8.98 ± 1.64 BW) produced a much higher
average peak GRF than the one-footed landing strategy (6.4 ± 1.57 BW), as seen in
Figure 7. This followed the same trend as the one-handed dunk trials with the two-footed
landing strategy producing greater GRF’s than the one-footed landing strategy.
Two-Handed Dunking
Peak GRF's( Based on BW)
12.0
10.0
8.0
One-Footed Landing Strategy
6.0
Two-Footed Landing Strategy
4.0
2.0
0.0
Figure 7. This is a graph of the two-handed dunk trials comparing the peak GRF values
between the one-footed and two-footed landing strategies. The two-footed landing
strategy average peak GRF was much higher than the one-footed landing strategy average
peak GRF.
Impulse
There was a significant difference in the impulse between the one and two-footed
landing strategies (F(1,7)= 7.782, p < 0.05, η2= .526). The average impulse for the twofooted landing strategy (719.23 ± 157.53 Newtons per second (N∙s)) was significantly
greater than average impulse for the one-footed landing strategy (602.83 ± 188.60 N∙s) as
seen in Figure 8.
41
One -Handed Dunk Impulse Averages
1000
*
Impulse (N∙s)
800
600
One-Foot Landing Strategy
Two-Footed Landing Strategy
400
200
0
Figure 8. This graph compares the average peak impulse values of the one-handed dunk
trials of the one and two-footed landing strategies. There was a significant difference (p <
0.05) between the average impulse of the one-footed landing and the average impulse of
the two-footed landing.
The two-footed landing strategy (927.29 ± 586.37 N∙s) produced a much higher
average impulse than the average impulse for the one-footed landing strategy (527.75 ±
182.62 N∙s), as seen in Figure 9. This followed the same trend as the one-handed dunk
trials with the two-footed landing strategy producing a greater average impulse than the
one-footed landing strategy.
Two-Handed Dunk Impulse Averages
1600
1400
Impulse (N∙s)
1200
1000
One-Foot Landing Strategy
800
Two-Footed Landing Strategy
600
400
200
0
42
Figure 9. This graph compares the average peak impulse values from the two-handed
dunk trials of the one and two-footed landing strategies. The two-footed landing strategy
average impulse was much higher than the one-footed landing strategy average impulse.
DISCUSSION
The results of the peak GRF analysis specify that the body experiences relatively
large landing forces during the typical basketball maneuver of dunking. Similar to
findings in McClay et al’s (1994) study, dunking a basketball is in a similar average
range of peak GRF’s than performing other jumping tasks in basketball (4.3-8.9 BW) in
the vertical direction.
Ground Reaction Forces
There was a big range in peak GRF between the participants (4.3-11.11 BW).
This high variability observed in the peak GRF’s among the basketball players may have
been partially due to the different amount of physical effort put forth in the movement.
Even though a script was read to each participant before to try and ensure maximal effort,
it was still difficult to motivate the athletes to perform dunks in a competitive manner in a
non-competitive lab setting. Some of the data may have been near-maximal effort, but the
large range of peak GRF’s were probably from varying sub-maximal efforts.
The main finding of this study was that the two-footed landing strategy produced
a significantly higher total peak GRF than the one-footed landing strategy. This caused
the researcher’s hypothesis to be rejected. When comparing the force absorbed by each
leg, Tillman et al. (2004) found that the one-footed landing (3.23 BW) showed almost
twice the GRF absorbed than the two-footed landing (1.86 BW). When performing the
two-footed landing strategy, the feet landed at the same time. This study shows how it is
related to Tillman et al.’s (2004) study by seeing the same trend of landing force with the
43
one-footed landing strategy (6.2 BW) producing almost twice as high peak GRF as the
two-footed landing strategy (3.83 BW) per leg. For the two handed dunk trials, the onefooted landing strategy would have a single leg absorb a peak GRF of 6.4 BW and the
two-footed landing strategy would have the legs absorb a peak GRF of 4.49 BW each.
Thus showing how asymmetrical landings can increase the likelihood of injury
occurrence in dunking a basketball.
Movements
In this study, the participants only jumped six times for the one handed dunk
trials, and twelve times if they participated in the two handed dunk trials. Instead of only
jumping six-twelve times in a laboratory setting, assume each player is jumping 50-70
times (based on position) per basketball game (Abdelkrim, Fazaa & Ati, 2006; Cumps,
Verhagen, & Meeusen, 2007). This means that each participant are applying 310-434 BW
for one-footed landings and 383-536.2 BW for two-footed landings for one-handed
dunks, 320-448 BW for one-footed landings and 449-628.6 BW for two-footed landings
for two-handed dunks to the lower extremities during a single game. This causes a lot of
stress on the ankle and knee joints from all the weight being applied from jump landings,
which can lead to the increased likelihood of injury (Tillman et al., 2004).
The participants of this study were asked to approach the basketball hoop from an
angle close to parallel with the baseline to prevent them from landing on the base. When
they jumped up for the dunk, the participants were jumping diagonally more than straight
ahead. Wikstrom et al. (2008) found that when landing from a diagonal and/or lateral
jumping task, the person is less dynamically stable than compared to those who land
straight ahead. The videos show how those participants, who landed more diagonally,
44
were stumbling a few feet before they were able to balance themselves while those who
landed straight ahead were able to stop and balance themselves instantly. Those who land
straight ahead and not diagonally will be able to control how balanced they are faster,
which in the long run, could reduce the likelihood of injury from occurring.
Impulse
The impulses were found to be significantly greater in two-footed landing strategy
(719.23 ± 157.53 N∙s) than the one-footed landing strategy (602.83 ± 188.60 N∙s) in onehanded dunk trials. They were also greater for the two-footed landing strategy (927.29 ±
586.37 N∙s) than the one-footed landing strategy (527.75 ± 182.62 N∙s) in the two-handed
dunk trials. The greater the impulses were from the dunk trials, the greater the change in
velocity there was from the flight phase to the landing phase. This greater change in
velocity can possibly create higher strain rates forced on the musculoskeletal system
(McClay et al., 1994).
Shock Attenuation
As this study proves, large amounts of force occur in a short period of time during
jump landings, which places a lot of strain on the lower extremities. As the body lands
from jumping tasks, the body has its own shock attenuation abilities. The body absorbs
some of the GRF through passive shock attenuation (bones, tendons, and soft tissue), but
active attenuation (joint angles and muscle activity) also plays a big part when it comes to
injury occurrence (Gross & Nelson, 1988).
Not only can the landing style, one or two-footed, affect how the landing forces
are attenuated within the lower extremities, but studies have shown how the use of proper
joint kinematics can lower these forces as well. Gross and Nelson (1988), and Valiant and
45
Cavanagh (1987) reported that landing on the forefoot instead of landing on the heel, or
flat footed, reduced the exposure to skeletal transients by about 50%. When landing on
the heel, the body absorbs up to 6 BW while the forefoot only lands with 3-4 BW. As the
foot lands on the forefoot, there is a greater range of motion in the joint, thus there is a
greater amount of time for the body to come to rest. Also, if the person lands on the heel,
there is usually a second peak GRF created because the forefoot and heel will land just
separately of each other and not at the exact same time. This second peak GRF increases
the likelihood of injury from occurring then because the lower extremities have to absorb
even more force than if they would if they just landed on the forefoot. In this study, there
were several subjects that had a second peak GRF, which indicates that they landed flat
footed instead of on their forefoot (Figure 10). The proper landing style based on foot
angle can play a huge role in injury prevention from jump task landings.
9000
Heel (Flat-Footed) Landing
Ground Reaction Force (N)
8000
7000
6000
OneFooted
Landing
5000
4000
3000
2000
1000
2.61
2.63
2.65
2.67
2.69
2.71
2.73
2.75
2.77
2.79
2.81
2.83
2.85
2.87
2.89
2.91
2.93
2.95
2.97
2.99
3.01
3.03
3.05
3.07
0
Time (s)
Figure 10. Illustration of the heel landing that causes two peak GRF’s when landing from
a dunk trail.
46
Muscle Activity & Injury
Studies have shown how EMG activity increases drastically in one-footed
landings compared to two-footed landings (Tillman et al., 2004; McKinley & Pedotti,
1992). There was a 28-72% muscle activity increase before landings when comparing
one-footed to two-footed landings. Muscle activity started in the ankle joints, then
moved to the knee joints, and then lastly the hip joints. Caulifield et al. (2004) and
Bisseling et al. (2008) found that when athletes who have functional instability in the
ankles land from a jumping task, they have significantly lower muscle activity than those
who have healthy ankles. This drop in muscle activity shows a trend of why it is so easy
for athletes to reinjure their ankles while playing basketball. Previous studies have found
that after the initial injury, 52.9% were reinjured with the majority of the re-injuries being
to the ankle (Cumps et al., 2007; Meeuwisse et al., 2003). Keeping the joints of the lower
extremities healthy is very important because research has seen how often the recurrence
of injuries really happens.
Strength Training
McInnes et al. (1995) had found in their study that basketball is a game of many
movements (995 ± 183). To keep up with all the changing of directions, plyometrics and
resistance training is necessary for basketball players to work on during the off-season.
Boracsynski and Urnaiz (2008) showed how the implementation of a plyometrics
workout routine had significantly (p < 0.05) improved the vertical jump height,
maximum jump speed, maximum jump power and impulse of force. Plyometrics can help
strengthen the lower extremities, especially around the joints. These improvements can
lead to the decrease in likelihood of injury.
47
For the athlete to get optimal strength training results, the best time for a
basketball player to perform resistance training and plyometrics is during the off season.
The off season gives the athlete the right amount of rest and recovery time in between
workouts. To make sure the athletes have the best aerobic capacity before the season
starts for the greatest recovery time, the basketball players would need to increase their
aerobic training during the preseason, while only performing resistance training 2-3 times
a week. During the season, the athlete should only be endurance training, which is 12-15
repetitions for 3 sets at a light weight (60-70% 1RM), twice a week to maintain strength
(Tavino, Bowers, & Archer, 1995).
Summary
The two-footed landing strategy had a significantly higher total peak GRF and
impulse than the one-footed landing strategy in the one-handed dunk trials. Similar trends
were observed in the two-handed dunk trials. Even though this resulted in rejecting the
study’s hypothesis, the high peak GRF from dunking a basketball were similar to the
findings in the study by Tillman et al. (2004), when comparing the jump landings as a
whole, and not per leg. This study and the study by Tillman et al. (2004) found that the
one-footed landings produced twice as much peak GRF per leg than the two-footed
landing strategy. It is the opinion of the researcher that basketball players should use the
two-footed landing strategy for a safer landing from dunking. Even though the twofooted landing strategy produced a significantly higher total peak GRF, landing on the
two feet disperses the forces between the two legs, which puts less strain on each leg.
48
Conclusions
Based upon the methodology utilized to collect data and the statistical analysis of
the collected data, the following conclusions were made:
1. The total peak GRF was significantly higher in the two-footed landing strategy than in
the one-footed landing strategy, resulting in the rejection of the researcher’s
hypothesis.
2. The impulse was significantly higher for the two-footed landing strategy than for the
one footed landing strategy.
3. The two-handed dunk trials followed a similar trend found in the one-handed dunk
trials with the total peak GRF and impulses being greater in the two-footed
landing strategy than in the one-footed landing strategy.
4. Even though the two-footed landing strategy produced a higher total peak GRF and
impulse than the one-footed landing strategy, it is safer to land on two feet than
one foot. When performing a two-footed landing, the force is dispersed between
two legs, which means that each leg will absorb less than the peak GRF. Less
strain placed upon each leg, will reduce the possibility of injury from occurring.
Recommendations
Based upon the conclusions reached in this study, future research could benefit by
following these recommendations:
1. Future research designs could increase the diversity and number of participants used
for data collection. There were only eight participants for this study, and three of
which that could perform a two-handed dunk. A sample size of 20 or higher could
give a greater effect size and may produce different results. Also, expanding the
49
basketball players recruited from just Division III and recreational players to
Division I or Professional level players could greatly increase the sample size.
The Division I and Professional levels would have more players who could dunk
a basketball, and more players who could dunk with two hands.
2. Future studies could use more than one camera to film the dunk trials. One camera
was used for the present study to film the dunk trial, but was placed at half court.
One place another camera could have been placed would be right by the landing.
The focus could be how the participants land on their feet, forefoot vs. heel
landings.
3. Another suggestion would be to keep the study close to where the recruitment of
participants takes place. In this study, many participants dropped out because of
having to travel to the test site, which was 40 minutes away. The closer the test
site is to the participants, the more likely they would stay in the study.
50
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55
Appendix A
Informed Consent
Subject
# _____
State University of New York College at Cortland
The study you have been asked to participate in is being conducted by Hans Wulf Jr. of
the Kinesiology Department at SUNY Cortland. Please read the following information,
and sign the freedom of consent section if you choose to participate.
Purpose and Explanation of Testing Procedures

The purpose of this study is to understand which landing strategy produces a
higher peak ground reaction force.

The research session you will be taking part in will consist of one day of data
collection. This day will depend on when you will be able to be tested. During this
session of research, you will be dunking a basketball with one hand and with two hands,
while landing in two different ways, one footed and two footed.

There will be several sessions of data collection taking place over several weeks
to ensure that each participant has the chance to attend one of them.

The measurement taken will include height, weight, vertical jump height, and
peak ground reaction forces for the vertical jump and dunk trials.

This study should take approximately one hour per subject to collect data.
Risk and Discomforts

The protocol for this study will cause no more risk or discomfort for the subject
than playing in a basketball game or practice. Maximum risk associated with the study
includes ankle sprains.

If at any point you wish to stop your participation in this study, please do not
hesitate to tell the test administrator.
Participant Responsibilities

Please communicate with the test administrator if your experience any problems
before, during, or after the study session.

Participants will need to supply their own transportation to and from the testing
site.

A Modified PAR Q & YOU will be asked to answer accurately to ensure all
participants are healthy enough to participate in the study. Those who are not healthy
enough to participate will be asked to not participate.
Benefits

This study will give basketball players the knowledge of which dunking style and
which landing strategy produces less peak ground reaction force. This knowledge can
lead to a decrease in likelihood from injury from occurring.
56

Participants will all receive a dvd copy of their dunk trials for participating in this
study.
Inquires

Test: Administrator: Hans Wulf Jr

Email Address: hans.wulfjr@cortland.edu

Phone #: 845-741-2728

For questions about research or research subjects’ rights, contact Amy
Henderson-Harr, IRB Designee, Office of Research and Sponsored Programs, SUNY
Cortland, at (607) 753-2511.
Use of Records

The results from the vertical jump tests and the dunk trials will be kept
confidential for each individual. You results will be identified by an assigned number, not
your name.

The only individuals who will have access to your information are the testing
administrator and assistant. Collected data will be stored in a locked cabinet.
Freedom of Consent

I have read the information on this page, and understand the potential risks and
discomforts of participation.

Any questions I have regarding this information were answered to my
satisfaction.

I consent to participate in this experimental study.
Participant’s Signature
__________________________ __________________ Date: ______________
Participant’s name (Printed)
__________________________ __________________ Date: ______________
Signature of Witness
__________________________ __________________ Date: ______________
57
Appendix B
Modified Physical Activity Readiness Questionnaire (PAR-Q)
Name
Date
DOB
Age
Unit
Work Phone
Regular exercise is associated with many health benefits, yet any change of activity may
increase the risk of injury. Completion of this questionnaire is a first step when planning
to increase the amount of physical activity in your life. Please read each question
carefully and answer every question honestly:
Yes
No
Don’t 1) Has a physician ever said you have a heart condition and you should only do
Know physical activity recommended by a physician?
Yes
No
Don’t
2) When you do physical activity, do you feel pain in your chest?
Know
Y
No
Don’t 3) In the past month have you had chest pain when you were not doing physical
Know activity?
Y
No
Don’t 4) Do you lose your balance because of dizziness or do you ever lose
Know consciousness?
Y
No
Don’t 5) Do you have a joint or bone problem that may be made worse by a change in
Know your physical activity? If yes, explain to HPC.
Yes
No
Don’t
6) Do you currently have high blood pressure that is not controlled by medication?
Know
Yes
No
Don’t
7) Do you have osteoarthritis?
Know
Yes
No
Don’t 8) Do you currently have an ankle or foot injury that could prevent you from
Know performing jumping tasks?
Yes
No
Don’t 9) Do you know of any other reason you should not exercise or increase your
Know physical activity?
Yes
Yes
Yes
Participant signature
Date
58
Members answering no to all questions may begin a moderately paced exercise program. If a
member answers yes to any of the above questions wait for clearance from physician to begin
exercise program.
Reference: ACSM’s Guidelines for Exercise Testing and Prescription, Sixth Edition, 2000
59
Appendix C
Arrival Script
Hello and thank you for your participation in my study. Today we are going to see
how high the peak GRF is from dunking one and two-handed, and from landing one and
two-footed. As a bonus for participating, you will receive a DVD of all your dunks
performed, upon request. They will be made up as soon as the study is complete.
To start today’s session, I will like all of you to review the informed consent and
Modified PAR-Q & You, answer the questions to the best of your ability, and sign them.
Once this is complete, you will be taken by my research assistant here to get your height
and weight recorded. Once that is complete, you will be given a 10 minutes warm-up
period. For 5 minutes you will perform a dynamic warm-up, which includes a slow jog,
high knees, butt kicks, skipping and shuffling.
We will start the dunk trials with the one-handed dunks. Landing strategy is
randomized based on order of arrival here as well. Six dunks will be performed, three per
landing strategy. Each dunk trial will be recorded using a JVC camcorder, so make the
dunks count.
For the two-handed dunk, a trial dunk will be asked to be performed to ensure you
can perform a quality two-handed dunk. If your two-handed dunk does not pass the
quality test, you will not be asked to perform the dunk. You can leave at this time or you
can stay to watch the others dunk. If your two-handed dunk passes the test to ensure
quality dunks are being performed, then you will perform 6 more dunks, 3 for each
landing strategy. Once all of your dunk trials have been performed, you will be allowed
to leave.
60
Once again, I would like to say thank you for participating. I greatly appreciate it.
I hope you all have fun and learn a lot from this study. Let’s get started.
61
Appendix D
Floor Layout
62
Appendix E
Data Collection Day #
Subject #
Date
Time
Position
.
1) Physical Measurements:
Age
years Height
cm Weight
kg
2) Peak Vertical Jump GRF Testing:
Peak GRF (N)
1
2
3
3) One-Handed Dunking Testing:
Landing Style
Peak GRF (N)
One-foot
One-foot
One-foot
One-foot Average
Two-feet
Two-feet
Two-feet
Two-feet Average
4) Two-handed Dunking Testing (if applicable): Yes
Landing Style
No
Peak GRF (N)
63
.
.
One-foot
One-foot
One-foot
One-foot Average
Two-feet
Two-feet
Two-feet
Two-feet Average
64
Appendix F
Randomized Order of Landing Style Being Performed for
Both One and Two-handed Dunking Styles
Order of Arrival
Landing Style to Perform First
Landing Style to Perform
Second
1
One-foot
Two-feet
2
Two-feet
One-foot
3
One-foot
Two-feet
4
Two-feet
One-foot
5
One-foot
Two-feet
6
Two-feet
One-foot
7
One-foot
Two-feet
8
Two-feet
One-foot
9
One-foot
Two-feet
10
Two-feet
One-foot
65
Appendix G
Dunking Script for Maximal Effort
I need you to dunk this ball with as much force as possible. I need you to attack
the rim like you are LeBron James. Just like you are going to dunk over Michael Jordan
and beat him at his game. This dunk needs to look good for the camera. Don’t you want
your friends to see how hard you throw down on DVD? You’ll be the only one of your
friends with a DVD of your own amazing dunks being performed. Now, when I tell you
to go, you dunk that basketball with so much force, your friend’s mouths will drop. Get at
it!
66
Appendix H
Procedure Matrix
Dunk 3 times
landing on one foot
One-handed
10 Minute Warm- Up
Period
Dunking
Volunteers
(5 minute dynamic
warm-up, 5 minutes
shoot around)
Random
Order
n= 8
Dunk 3 times
landing on two feet
If they can dunk
with two hands
then follow
procedures below
Dunk 3 times landing
on one foot
Two-handed
Dunking
Volunteers
Random Order
n=5
Dunk 3 times landing
on two feet
67