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EFFECTS OF DIFFERENT BACKPACKS ON SELECTED GAIT PARAMETERS IN COLLEGE STUDENTS
DANIEL B. JENSEN1, PAIGE DENNEY1, JASON V. SLACK1, MICHAEL BOHNE1
1Department
of Exercise Science and Outdoor Recreation, Utah Valley University, Orem, UT, USA
Abstract
Jensen DB, Denney P, Slack JV, Bohne M. Effects Of Different Backpacks On Selected Gait
Parameters In College Students. Journal of Undergraduate Kinesiology Research, 2014; 9(2):
41-46. Purpose: Various studies have evaluated how backpacks affect adolescent school
children’s gait parameters and posture. No studies have been found that evaluate those same
gait parameters and posture aspects in college students. The aim was to evaluate the trunk
flexion, gait velocity, foot angles (toe-in/toe-out), single vs. double foot support and cadence in
college students when wearing backpacks loaded with a set weight of 14 lbs. Methods: 29
students (23±3.77 yr) were randomly recruited from the student body at Utah Valley University.
The equipment used included reflective markers, a video camera, and a 20 ft Gaitrite system
(CIR Systems, Havertown, NY). The participants walked across the Gaitrite 10 times per
condition for each of the five conditions. The five conditions include the Control (no bag), Red
Messenger Bag (RMB), Grey Messenger Bag (GMB), Curved Strap Bag (CSB) and Straight
Strap Bag (SSB). Trunk flexion, foot angles, the time spent in single and double support and
walking velocities were recorded, evaluated and compared. Results: Trunk flexion was
observed in all backpack conditions. The control had a mean trunk angle of 91˚ ± 4˚ the RMB
was 89˚±5˚, the CSB was 86˚±5˚, the SSB was 87˚±5˚, and the GMB was 88˚±5˚. The SSB,
CSB, and GMB affected gait velocity. The other gait parameters were affected differently
respective to the condition. Conclusion: Even at the college level, the weight carried within
backpacks causes an increase in trunk flexion, alters the gait velocity, decreases the amount of
time spent in single foot support, and has the potential to alter hip rotations. With all of these
alterations combined, it is fair to say that college students carry an unacceptable amount of
weight in their backpacks.
Key Words: Trunk Flexion, Single and Double Support, College Students
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INTRODUCTION
There is one main piece of equipment used by almost every school student throughout
the entire world, the backpack. The term “backpack” is a broad term in its definition.
Backpacks come in various sizes, shapes and brands. They also come with various
types of straps. Some backpacks have single straps, some have two straps and some
have extendable handles for pulling the bag behind as you walk. Single strap bags are
typically known as messenger bags or briefcases. The bags with two straps typically
come with one of two different strap styles. The first style of strap is straight. The
second style of strap is curved and more ergonomically shaped.
There have been studies done on elementary school students and middle school
students that address the physiological effects of weighted backpacks. Negrini and
Carabalona found a correlation between heavy backpacks and back pain in adolescents
(Negrini & Carabalona, 2002).
Lindstrom-Hazel evaluated the question of
schoolchildren and how much weight they should carry in their backpacks before it
causes back pain and couldn’t find a solution in the literature they reviewed and didn’t
suggest any solutions to try (Lindstrom-Hazel, 2009).
Evidence shows that when the backpack load is above 15% of the student’s body
weight, it causes significant increases in trunk flexion along with alterations to the stride
length and frequency (Bauer & Freivalds, 2008; Pascoe, Pascoe, Wang, Shim, & Kim,
1997; Shasmin, Osman, Razali, Usman, & Abas, 2007). However, there is a lack of
research conducted on the college age demographic in relation to backpacks and any
health risks they may impose. The previous studies (Negrini & Carabalona, 2002;
Lindstrom-Hazel, 2009; Bauer & Freivalds, 2008; Pascoe, Pascoe, Wang, Shim, & Kim,
1997; Shasmin, Osman, Razali, Usman, & Abas, 2007) may not have addressed the
college demographic, but they did serve as the inspiration to finding out how different
backpacks affect gait parameters and trunk flexion within college students.
In college it seems that the student’s worry less about how much weight they have in
the backpacks and instead focus on making sure they have everything they need. Like
most people, college students also appear to be creatures of habits. Because of this, it
was deemed more applicable to use a set amount of weight instead of an ever-changing
body weight percentage. With this set weight, we hypothesized the average load
carried by college students causes alterations to their posture and gait patterns.
METHODS
Subjects
The participants of this study were randomly selected from the Utah Valley University
(UVU) student population. There were a total of 29 participants, 15 males and 14
females. The participants had an average age of 23 years old (± 3.77 years), a height
of 173.2 cm (± 9.7 cm) and an average weight of 172.3 lb. (± 44.8 lb.). All participants
signed an Institutional Review Board approved informed-consent form.
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Instrumentation
The equipment used for this study includes a SECA slide scale (SECA, Hamburg,
Germany) that was used to establish the average backpack weight of UVU students and
a 20 ft. GaitRite System (CIR Systems, Havertown, NY) used to measure the gait
parameters of stride length, stride rate, foot angle (toe-in/toe-out) and percent of single
and double support. A Casio EX-FH25 (Casio, Tokyo, Japan) was used to record all
videos at 30 Hz. MaxPro Motion Analysis Software (Innovision Systems, Ann Arbor, MI)
was used to digitize and analyze the video of each participant walking. The statistics
were analyzed using SPSS 17.0 (IBM, Armonk, NY).
Procedures
In a pilot study done at Utah Valley University (UVU), it was determined that the
average UVU student’s backpack weighs 14 lb. This was regardless of age, gender,
year in school or major. It was also discovered that there were three main different
backpack styles utilized by the student population. Those styles included backpacks
with straight shaped shoulder straps, backpacks with more ergonomically shaped
curved shoulder straps and messenger bags that only have one shoulder strap. This
information was then utilized for this study.
Including the Control, there were five conditions. The other conditions were the Red
Messenger Bag (RMB), the Grey Messenger Bag (GMB), Curved Strap Bag (CSB) and
the Straight Strap Bag (SSB) (see Figure 1). The tradition backpacks differ from each
other in their strap design. The curved straps are designed to be more ergonomic and
help people wear their backpack more comfortably. The straight straps found on the
other backpack are found on backpacks that are traditionally cheaper in design. The
messenger bags also differ from each other in their construction. The Red Messenger
bag was smaller and designed as more of a hip bag with a shoulder strap. The Grey
Messenger bag was designed as an office bag capable of carrying a 17” laptop. The
participants walked across the 20 ft. GaitRite System for ten trials per loaded condition
and ten trials for the unloaded Control condition for a total of 1000 ft. The unloaded
condition acted as the control for each participant.
Figure 1. From left to right, the Curved Strap bag, the Straight Strap Bag, the Red
Messenger Bag (RMB), and the Grey Messenger Bag (GMB).
The loaded conditions included four different styles of backpacks loaded with 14 lb. All
participants wore three reflective markers; above the right ear, on the greater tubercle of
the Humerus and on the greater trochanter of the Femur bone. Trunk flexion was
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measured as an absolute angle relative to the vertical plane. Every trial was recorded
at 300 Hz. and then the video data was digitized and analyzed.
Statistical Analyses
Postural positioning and gait parameters were analyzed. The data was processed
using a repeated measures ANOVA with a family-wise alpha level set at 0.05.
RESULTS
Every loaded condition caused significant trunk flexion compared to the control group
(RMB p = 0.041, CSB p < 0.001, SSB p < 0.001, GMB p < 0.001). Within the loaded
conditions, the RMB caused less trunk flexion than both of the CSB (p = 0.005) and the
SSB (p = 0.01) (see Table 1).
The right foot angle in the control was different from the foot angle in the GMB (p=
0.049) and the RMB (p = 0.002). The right foot angle in the RMB was different to the
right foot angle when wearing the CSB (p <0.001) and the SSB (p = 0.004). The right
foot angle with the GMB was different when wearing the CSB (p = 0.049) and the SSB
(p = 0.043). The stride length of the control was different from stride length with the
GMB (p = 0.024). The amount of time spent in double foot support compared to time
spent in single foot support during the control was significantly different for all loaded
conditions (p < 0.001). The gait velocity during the control was different during the CSB
(p = 0.016), the SSB (p = 0.034) and the GMB (p = 0.006). The cadence (step/min)
during the control was different with the CSB (p = 0.006) and the GMB (p = 0.026).
Table 1. The Mean and Standard Deviations for each bag type and gait variable.
Bag
Mean Trunk Angle
(Degree)
Right Foot Angle
(Degree)
Stride Length
(m)
Velocity
(m/s)
Cadence
(step/min)
Control
91 ± 4
5.58 ± 4.73
140.55 ± 2.74
125.94 ± 2.73
107.78 ± 1.33
RMB
88.98 ± 5*
4.75 ± 5.11*
139.09 ± 2.66
124.12 ± 2.86
107.36 ± 1.38
CSB
86 ± 5*,**
5.44 ± 5.12**,^
139.75 ± 2.72
123.76 ± 2.67*
106.44 ± 1.27*,**
SSB
87 ± 5*,**
5.55 ± 4.92**,^
138.99 ± 2.62
123.45 ± 2.73*
106.71 ± 1.40
GMB
88 ± 5*
4.99 ± 5.23*
138.56 ± 2.51*
122.93 ± 2.60*
106.65 ± 1.28*
* = Different compared to control, ** = Different compared to the Red Messenger Bag,
^ = Different compared to the Grey Messenger Bag. (p < 0.05)
DISCUSSION
All of the loaded conditions caused an increase in trunk flexion. In this study, trunk
flexion was measured as an absolute angle. In previous studies, significant trunk
flexion was found when backpacks were loaded with 15% body weight (Bauer &
Freivalds 2008; Pascoe, et. al., 1997; and Shasmine, et al., 2007). In the current study
the average weight of our tested subjects was 172 lb. ± 44.75 lb. With that weight
range, the 14 lb. test weight is equivalent to 6.5% to 11% of the subject’s body weight.
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However, despite the low body weight percentage, the 14 lb. bags still caused
significant trunk flexion.
The use of a set weight of 14 lbs also seemed more applicable to real-world settings
compared to using a body weight percentage. College students of all sizes are required
to carry the same books and supplies. Through observation, it also seems that the
range of body weight found within college students is much larger than the body weight
range of elementary school students. Due to this variance, the use of a set weight was
deemed appropriate.
It is possible that long term use of backpacks could be the cause of back pain and other
back problems. The shearing forces acting on the spinal column could be increased by
increasing the forward flexion of the spine (Jager and Luttmann, 1992).
Also, an
association between backpack use and low back pain has been verified (Sheir-Neiss,
G.I., Kruse, R.W., Rahman, T., Jacobson, L.P. and Pelli, J.A., 2003). Sheir-Neiss et al.
evaluated backpacks worn to manufacturers’ specifications and since a lot of college
students don’t appear to follow those guidelines, the importance of the researcher’s
statement is probably understated. This association could also be the inspiration of
some backpack manufacturers producing bags with straps they claim are more
ergonomically friendly (curved strap bags).
One of the gait parameters that showed differences was the angle of the right foot; the
data showed that the two messenger bag conditions had significantly different angles
compared to the other conditions, probably due to the contralateral bag position. With
enough use of a messenger bag, overuse injuries could occur within the rotated hip,
causing pain and discomfort while walking.
There was a significant time increase in double support for all conditions. An increase
in load carriage causes a decrease in stability, causing a need to increase the time
spent double support. More time spent in double support causes a slower gait velocity.
In conclusion, college students currently carry too much weight in their backpacks. The
average weight carried by UVU students caused an increase in trunk flexion regardless
of age, gender or year in school. The load carried in the backpacks also slowed gait
velocity, increased time spent in double support, and with the messenger bags caused
a change in the right foot angle implying that the hip was rotated due to the contralateral
bag placement. In an effort to avoid such potentially harmful conditions, college
students should avoid using messenger bags, should always follow the manufacturer
settings for proper bag positioning, and carry less weight in their backpacks.
Unfortunately, lightening the load carried by college students isn’t as easy as it sounds.
Some ideas include the use of eTextbooks and typing notes on a laptop instead of using
pen and paper. This would eliminate the weight of the textbook and the weight of the
notebook while not increasing the weight carried by the student. The influx of
“ultrabook” laptops and tablet pc’s also work in favor of reducing weight. These items
are significantly lighter than normal laptops but ultrabook laptops come at a steep price
tag and tablets aren’t ideal for typing notes on. As for backpack positioning and
Backpacks and Gait Parameters
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posture, following the manufacture’s guidelines for proper backpack positioning is a
really important part of using backpacks that often gets ignored by college students. A
possible solution for this could be more visible warnings and instructions on the
backpack labels.
This particular solution lies in the hands of the backpack
manufacturers but it is a relatively simple one that has the potential to help solve part of
this problem.
Address for correspondence: Jason V. Slack, PhD, Department of Exercise Science
and Outdoor Education, PE 147K, 800 West University Parkway, Utah Valley University,
Orem, UT 84058, Phone: (801) 863-7488, Email: jason.slack@uvu.edu.
REFERENCES
1. Bauer, D. H., & Freivalds, A. (2008). Backpack load limit recommendation for middle
school students based on physiological and psychophysical measurements. Work,
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2. Jager, M. and Luttmann, A., (1992). The load on the lumbar spine during
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3. Lindstrom-Hazel, D. (2009). The backpack problem is evident but the solution is less
obvious. Work, 32(3), 329-338.
4. Negrini, S., & Carabalona, . (2002). Backpacks on! School children's perceptions of
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5. Pascoe, D. D., Pascoe, D. E., Wang, Y. T., Shim, D, & Kim, C. K. (1997). Influence
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The association of backpack use and back pain in adolescents. Spine, 28, 922–930.
Disclaimer
The opinions expressed in the Journal of Undergraduate Kinesiology Research
are those of the authors and are not attributable to the Journal of Undergraduate
Kinesiology Research, the editorial staff or Western State Colorado University.