The effect of backpack heaviness on trunk-lower extremity muscle activities and trunk posture.

The purpose of the present study is to analyze trunk-lower extremity muscle activities and trunk postural changes during the carriage of different backpacks. Nineteen male university students (21+/-3 years) participated in the experiment's four standing modes: (1) unloaded standing, (2) 10% body weight (BW) load (in the form of a backpack), (3) 15% BW load and (4) 20% BW load. Bilateral rectus abdominis, erector spinae, vastus medialis and biceps femoris muscle activities were recorded using surface electromyography (SEMG), while trunk inclination, side flexion and rotation were measured by using VICON 250 during all standing modes. The results showed that rectus abdominis muscle activities increased progressively and disproportionably as the backpack load increased. As for the trunk posture, almost the same backward inclination was adapted even with increasing backpack heaviness. Twenty percent BW backpack causes the most significant muscular and postural changes so it should be avoided. However, it is recommended to study other backpack factors such as frequency of usage, usage time, type of the backpack and age to come up with a complete usage recommendation.