The Effect of Backpack Carriage on Myoelectric Variables of Selected Lower Extremity Muscles in Girls and Boys with 7-10 Years Age during Forward and Backward Walking

Backpack is the most common tool for carrying school supplies in children and adolescents as their constant companion during the school year and even daily life. The aim of the present study was to investigate the effect of carrying backpacks with different weights on the electromyographic variables of selected lower-limb muscles of 7-10 years old girls and boys during backward and forward walking. 

A total of 26 healthy students (13 boys and 13 girls) were included in the present study using convenience sampling. Subjects performed forward and backward walking while carrying a backpack under different conditions: 0% (no weight), 10%, 15%, and 20% of their body weight. Electrical activity of the muscles of rectus femoris, biceps femoris, tibialis anterior peroneus longus, and gastrocnemius medialis muscles of the dominant leg was recorded. Repeated measures ANOVA along with Bonferroni correction coefficient test was used to compare the dependent variables under these four conditions (P<0.008). 

Overall, the results of the present study showed that normalized mean activation of lower-limb muscles was significantly increased while carrying the backpacks with 15% and 20% of body weight during backward and forward walking (P<0.008); however, there was a significant reduction in the median frequency of the muscles under these two conditions during backward and forward walking (P<0.008). In contrast, there was no significant difference between different backpack weights in terms of the co-contraction rate of the dominant knee and ankle joints during backward and forward walking (P<0.008).

It seems that increasing the activity level and decreasing the median frequency of selected lower-limb muscles while carrying backpacks with weighting 15% and 20% of body weight  likely cause earlier fatigue and musculoskeletal injuries due to overwork; therefore, it is recommended that the backpack weight should be less than this range and close to 10% BW. Future studies are necessary to investigate other biomechanical aspects.