Background: Conventional backpack straps are flexible. Due to this flexibility, backpacks freely move on the human back. In this study, a new design of backpacks with non-flexible straps is proposed.
Objective: The aim of the present research is to demonstrate the possible differences between normal gait and steps while participants carry two different backpacks.
Methods: In this investigation, 9 healthy male college students were recruited with mean age, height and weight of 24.6 years, 179.6 cm and 76.41 kg, respectively. Each backpack was tested in two different steps. First, the participants were asked to walk on a treadmill, whose velocity was changed from 1.5 m/s to 2.5 m/s, for 15 minutes. Initial velocity was 1.5 m/s and the velocity increased 0.5 m/s in 5 minutes increments. In the next step, they walked for 15 minutes with constant velocity of 3 m/s. Head, neck, and trunk flexion or extension, lateral displacement, and velocity of the subjects during backpack carriage were compared with the obtained values during normal gait, when they walked without carrying a backpack. In addition, the level of discomfort (3 grades: Low, medium, severe) in the neck, shoulder, lumbar, upper and lower leg muscles were investigated by using a modified standardized questionnaire.
Results: By wearing the modified design of backpack, trunk flexion decreased while there was no significant (p > 0.05) change in velocity and lateral displacement. According to the questionnaire reports, more than 80% of the participants believed that both backpack discomfort in the neck (anterior side) and upper and lower legs were low. More than 75% of the subjects believed that by using a modified backpack, discomfort decreased for muscles in the neck (posterior), shoulder (posterior) and lumbar muscles. About 60% of both backpack users reported low discomfort in anterior shoulder muscles.
Conclusion: Backpacks cause some bad effects on kinematics of gait. In this study, by testing modified backpacks, some improvements were seen, specifically in posture, which may be useful to reduce side effects of backpack carrying.
Keywords: Gait analysis; backpack injury; design; ergonomics.