Vertical Jump Assessment Device
6
Journal of Exercise Physiologyonline
(JEPonline)
Volume 12 Number 3 June 2009
Managing Editor
Tommy Boone, PhD, MPH
Editor-in-Chief
Jon K. Linderman, PhD
Review Board
Todd Astorino, PhD
Julien Baker, PhD
Tommy Boone, PhD
Larry Birnbaum, PhD
Lance Dalleck, PhD
Dan Drury, DPE
Hermann Engals, PhD
Eric Goulet, PhD
Robert Gotshall, PhD
M. Knight-Maloney, PhD
Len Kravitz, PhD
James Laskin, PhD
Derek Marks, PhD
Cristine Mermier, PhD
Daryl Parker, PhD
Robert Robergs, PhD
Brent Ruby, PhD
Jason Siegler, PhD
Greg Tardie, PhD
Chantal Vella, PhD
Lesley White, PhD
Ben Zhou, PhD
Official
Research Journal of
the American Society of
Exercise Physiologists
(ASEP)
ISSN 1097-975
Equipment Testing and Validation
Validity of Alternative Field System for Measuring Vertical Jump
Height
ALEXANDER T. HUTCHISON, AMANDA L. STONE
Department of Exercise and Sport Science/St. Mary’s University, San Antonio,
Texas USA
ABSTRACT
Hutchison AT, Stone AL. Validity of an alternative system for
measuring vertical jump height. JEPonline 2009;12(3):6-11. The vertical
jump is an essential skill for improved athletic performance in sports that
require short, ballistic motions such as volleyball, basketball, football,
and diving. The purpose of the current study was to estimate the
concurrent validity of a new vertical jump height measuring device, the
Vertical Jump Mat (VJM), using a criterion field measure, the Vertec. A
group of 20 regularly active undergraduate students (10 male and 10
female) from the St. Mary’s University campus volunteered for the study
(mean age 21.0 ± 3.2 yrs, mean height 171.0 ± 10.7 cm, mean weight
72.0 ± 12.2 kg). A significant relationship was observed (R² = 0.83, P <
0.001) between vertical jump height scores measured with the VJM and
the Vertec. The VJM is a valid measure of vertical jump height. This
simple, portable device is specifically suited to assess athletic
improvement in response to a particular training regimen.
Key Words: Vertical Jump, Biomechanics, Athletic Assessment, Vertec
Vertical Jump Assessment Device
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INTRODUCTION
Vertical jump height is an objective functional measurement used to assess strength in the extensor
muscles of the lower extremities, and to estimate anaerobic power and capacity (1-3) The ability to
perform a maximal vertical jump is considered by many coaches to be an essential skill in several
sports including football, volleyball, basketball, and certain track and field events (4-6) Vertical jump
height is often assessed as a marker of an athlete’s improvement in response to training, and has
recently been used as an objective measure of post-operative leg health and function (7,8).
There are many methods and commercially available devices used to measure vertical jump height.
The “gold standard” criterion method is a video technique that measures the vertical displacement of
a series of reflective markers that are placed on the body (9). This method, although considered to
be highly valid, requires expensive motion analysis equipment, extensive training, and is impractical
for field assessments.
A popular field method for measuring vertical jump height is the jump and reach test, during which
jump height is measured as the highest point that a subject can reach to touch an over-head object.
One commonly used, commercially available device, the Vertec (Vertec Sports Imports, Hilliard, OH),
consists of a series of colored plastic vanes that are placed 0.0127 m apart on a telescoping
aluminum pole that can be adjusted to the subject’s standing reach. The subject performs a maximal
jump and swats at the plastic vanes at the peak of the jump. Vertical jump height is measured as the
vertical distance between the standing reach and the highest vane displaced by the subject’s hand at
the peak of the jump. Although it has been shown to be a valid and reliable device [12], it is relatively
expensive. Additionally, the Vertec is several feet tall and requires the use of bulky counterweights to
prevent it from tipping over during testing. To that end, the purpose of this study is to validate the use
of a recently developed field instrument, the Vertical Jump Mat (VJM, Sport Books Publisher, Toronto,
Ontario, CA) against to the Vertec. Relative to the Vertec, the VJM has specific advantages for use in
the field including portability, ease of use, and relative inexpensiveness. We hypothesize that the
vertical jump height measures obtained by the VJM can be used to predict vertical jump height
measures obtained from the Vertec.
METHODS
Subjects
A group of 20 regularly active undergraduate students (10 male and 10 female) from the St. Mary’s
University campus volunteered for the study (mean age 21.0 ± 3.2 yrs, mean height 171.0 ± 10.7 cm,
mean weight 72.0 ± 12.2 kg). The research was approved by the Committee for the Protection of
Human Subjects at St. Mary’s University. All subjects signed informed consent and were able to
withdraw at any time during the course of the study.
Vertical Jump Testing
Because vertical jump is a complex, multi-joint motion, each subject was allowed three familiarization
jumps. Each subject was tested once, and each test consisted of two maximal vertical jumps. The
average height of the two jumps was used. There was a recovery period of 30 seconds between
each jump provided during both familiarization and true measure.
The VJM consists of a tape measure feeder anchored to a rubber mat (Figure 1). The subject wore a
belt around the waist that was attached to one end of the tape measure. Each subject stood with
their feet shoulder-width apart and legs straight. The tape measure was threaded through the feeder
until the 0 cm mark. This was set as the reference point. When the subject jumped, the tape
measure was pulled through the feeder. The vertical jump height was measured as the total length of
the tape.
Vertical Jump Assessment Device
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measure that was pulled through the
feeder. Simultaneous measures of
vertical jump were obtained from both
devices to eliminate any inter-session
variability. The VJM was placed on
the ground adjacent to the Vertec
such that the plastic vanes were
directly above the VJM.
Statistical Analysis
A Priori sample size calculations were
completed prior to the study using Gpower (v.2.0; Bonn, Germany). In
order to obtain an effect size
correlation of 0.71 (α =.05, β = 0.10;
power = 90%), corresponding to an R2
of 0.50, indicating 50% common
variance between the two measures,
at least 11 subjects were required.
Due to the non-invasive nature of the
measurement, we increased the
number of subjects to 20 to decrease
the possibility of a type II error.
The reliability of each mode of vertical
jump testing was determined using
intraclass correlation coefficients (ICC
2,2) and the associated standard error
of measurement (SEM).
The
relationship between the two modes of
vertical jump testing was determined
using linear regression with vertical Figure 1. Vertical Jump Mat.
jump height measured with the Vertec
as the dependant variable and vertical jump height measured with the VJM as the predictor variable.
Statistical significance was set at the 0.05 α level. Analyses were performed using SPSS version
15.0 (SPSS Inc., Chicago, Ill).
RESULTS
Means and standard deviations of all measures are presented in Table 1. The vertical jump height
measured with the Vertec ranged
Table 1. Relationship between vertical jump height measurements
from 31.1 cm to 76.2 cm. The
made with the Vertec and VJM.
vertical jump height measured
Vertec (cm)
VJM (cm)
R
R2
SEE
P value
with the VJM ranged from 31.4
48.83 ± 13.14 52.40 ± 14.12
0.91
0.83
5.52
< 0.001
cm to 79.1 cm. The reliability
(ICC 2,2) of the Vertec measures
Vertec and VJM measures are means ± SD. SEE is the standard
was 0.99. The SEM for the
error of the estimation in cm.
Vertec measures was 1.47 cm.
The reliability (ICC 2,2) of VJM measures was 0.99. The SEM for the VJM measures was 2.39 cm.
Vertical Jump Assessment Device
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A statistically significant correlation was observed between Vertec and VJM measures of vertical
jump height (Table 1). The validity coefficient exceeded the criterion value (r ≥ 0.71) (r = 0.91, P
<0.001, Figure 2). The standard error of the estimation for the prediction of vertical jump height using
the Vertec from the jump height using the VJM was 5.5 cm.
DISCUSSION
The strong association between Vertec and VJM measures of vertical jump height indicates that
concurrent validity exists between the VJM and the Vertec in this population. The common variance
between the modalities was 83.3%. Additionally, the correlation coefficient was greater than 0.80, an
acceptable
value
for
concurrent validity (10). If the
ability to perform a vertical
jump
is
a
general
characteristic, then any testing
modality should be able to
discriminate
between
individuals who can jump high
and those who cannot and
rank
them
accordingly.
Evidence for the validity of this
concept of “generality of
vertical jump height” would be
a
Pearson
Correlation
Coefficient, r of 0.71 or greater
between two different jump
tests (11). A validity coefficient
of 0.71 corresponds to an R2 of
0.5, meaning that the two tests
share at least 50% common Figure 2: Scatterplot of vertical jump height (cm) measured with the
variance,
which
is
a Vertec as a function of vertical jump height measured with the VJM
reasonable
threshold
for (cm).
prediction of performance in
one testing modality using the results of another as a proxy measure.
The average vertical jump height obtained with the Vertec was significantly lower than that obtained
with the VJM (48.8 cm and 52.4 cm respectively, P = 0.012). Similar results were observed by Leard
et al. (2007), who compared the Vertec to the video analysis method (12). The average Vertec
measure was 4.3 cm lower than that observed with video analysis. The authors speculated that the
Vertec provided an underestimation of jump height because the subjects would miss-time when they
swatted at the vanes (i.e., catching them after the peak and on their way back down). We observed
this same phenomenon. When assessing the individual data points, this same relationship was
observed in 17 of the 20 subjects. Interestingly, only the three subjects (two volleyball players and
one basketball player) who had higher vertical jump scores using the Vertec had prior experience with
the device. Although we were unable to directly compare the VJM to the video analysis method, the
margin of difference between the VJM and the Vertec (3.6 cm) in the current study is similar to
difference observed between the video analysis method and the Vertec (4.3 cm) in Leard et al. This
provides further supporting evidence as to the validity of the VJM. However, future study should
focus on validating the VJM against the video analysis method as well.
Vertical Jump Assessment Device
10
Although our sample was larger than what was necessary to achieve our statistical objectives, care
should still be taken when interpreting these results past the confines of the population tested, i.e.
recreationally active college-aged students. Future studies should test other suitable populations
such as the young and those undergoing rehabilitation following an injury. The VJM will provide a
useful addition to the current register of devices used to measure vertical jump height. The VJM can
be used to routinely monitor vertical jump height in a simple, safe, and cost effective manner that is
well suited to use in the field.
CONCLUSIONS
In conclusion, the VJM is a valid field device for the measurement of vertical jump height in
recreationally active, college-aged subjects. The VJM offers specific benefits when compared to
other methods for measuring vertical jump including affordability, ease of use, and portability.
ACKNOWLEDGEMENTS
The VJM was provided by Sport Books Publisher, (Toronto, Ontario, CA). The authors would like to
acknowledge the contribution of Brad Bulycz for his assistance in equipment acquisition.
Address for correspondence: Hutchison AT, PhD, Department Exercise & Sport Science, St.
Mary's University, San Antonio, Texas, USA, 78228. Phone (210) 431-8027; FAX: (210) 436-3040;
Email. latinscotsman@gmail.com.
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