EFFECTS OF DIFFERENT BACKPACKS ON SELECTED GAIT PARAMETERS IN COLLEGE STUDENTS

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1 Backpacks and Gait Parameters 41 EFFECTS OF DIFFERENT BACKPACKS ON SELECTED GAIT PARAMETERS IN COLLEGE STUDENTS DANIEL B. JENSEN 1, PAIGE DENNEY 1, JASON V. SLACK 1, MICHAEL BOHNE 1 1 Department 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): 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

2 Backpacks and Gait Parameters 42 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 cm (± 9.7 cm) and an average weight of lb. (± 44.8 lb.). All participants signed an Institutional Review Board approved informed-consent form.

3 Backpacks and Gait Parameters 43 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

4 Backpacks and Gait Parameters 44 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 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 ± ± ± ± ± 1.33 RMB ± 5* 4.75 ± 5.11* ± ± ± 1.38 CSB 86 ± 5*,** 5.44 ± 5.12**,^ ± ± 2.67* ± 1.27*,** SSB 87 ± 5*,** 5.55 ± 4.92**,^ ± ± 2.73* ± 1.40 GMB 88 ± 5* 4.99 ± 5.23* ± 2.51* ± 2.60* ± 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. ± lb. With that weight range, the 14 lb. test weight is equivalent to 6.5% to 11% of the subject s body weight.

5 Backpacks and Gait Parameters 45 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

6 Backpacks and Gait Parameters 46 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) , 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, 32, Jager, M. and Luttmann, A., (1992). The load on the lumbar spine during asymmetrical bimanual materials handling. Ergonomics, 35, Lindstrom-Hazel, D. (2009). The backpack problem is evident but the solution is less obvious. Work, 32(3), Negrini, S., & Carabalona,. (2002). Backpacks on! School children's perceptions of load, associations with back pain and factors determining the load.spine, 27(2), Pascoe, D. D., Pascoe, D. E., Wang, Y. T., Shim, D, & Kim, C. K. (1997). Influence of carrying book bags on gait cycle and posture of youths. Ergonomics,40(6), Shasmin, H. N., Osman, N. A., Razali, R., Usman, J., & Abas, W. A. B. (2007). The effect of load carriage among primary school boys: a preliminary study. Journal of Mechanics in Medicine and Biology, 7(3), Sheir-Neiss, G.I., Kruse, R.W., Rahman, T., Jacobson, L.P. and Pelli, J.A., (2003), The association of backpack use and back pain in adolescents. Spine, 28, 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.