During asymmetrical backpack loading: Is unloaded side of body segments truly unloaded?

Abstract

Most of school age adolescents carry their backpacks by different methods such as carrying over 1 shoulder or 2 shoulders. According to investigations, most of them also have musculoskeletal complaints. Some studies indicate that backpack carriage method could be one of the risks of musculoskeletal problems in these age groups. Biomechanical responses during asymmetrical backpack loading have been investigated. However, both kinematics and time–distance parameters were not investigated together. The aim of this study was to investigate the biomechanical alterations seen at the unloaded side during asymmetrical backpack loading relative to unloaded gait. 7 female, 13 male adolescents with a mean age of 13.36(±1.6) years were evaluated under two conditions; unloaded gait (walking without a backpack) and unilateral loaded gait (walking with backpack that is 15% of body weight) over one shoulder. Time–distance and kinematic parameters of gait at self-selected speed were recorded by motion analysis system. The statistical differences between two conditions were analyzed by paired-t test. The study showed that peak ankle dorsiflexion, range of hip motion in the sagital plane, mean hip abduction during stance, range of pelvic tilt increased and mean pelvic obliquity decreased at the unloaded side during unilateral loaded condition relative to unloaded gait. Temporal parameters showed that stance period (%Gait cycle) and double support period (%Gait cycle) increased and swing period (%Gait cycle) decreased significantly on the unloaded side when compared with unloaded gait. The present study showed that during unilateral backpack loading, the unloaded side is not truly unloaded. It demonstrated that some biomechanical alterations occur on the unloaded side. Increase in range of motion may be related to increased energy consumption and compensation of the loaded side’s kinematic alterations. Findings related to time–distance parameters may reflect the compensation of stance phase instability on the loaded side. Therefore, by lengthening the duration of time in stance phase of the unloaded side, it is exposed to load for a longer time than the loaded side. This is in contrast with expected results that the loaded side may manifest the effects of mechanical stress in years. Consequently, the unloaded side as well as the loaded side should be carefully examined and monitored by clinicians.