Effects of varying backpack loads on peak forces in the lumbosacral spine during walking

OBJECTIVE: To compare the differences in lumbosacral spine forces under varying backpack loads. DESIGN: A biomechanical model was used to determine the changes in peak forces in the L5/S1 joint with increasing backpack loads during level walking. BACKGROUND: Most studies involving varying external backpack loads have been concerned mainly with kinematic and physiological measurements. To the author's knowledge, there has been no investigation of the change in peak forces in the lumbosacral joint during the carriage of such loads. METHOD: Data acquisition was carried out using a 5-camera Vicon motion analysis system and two Kistler force plates. Ten male subjects with similar weights, height and age were recruited for this study. Three different backpack loading conditions were studied, that is walking with no load, with 15% BW and with 30% BW. RESULTS: It was observed that all the ten subjects while walking with heavier backpack load adopted a compensatory trunk flexion posture. However, kinematic gait parameters such as walking speed and stride length remained unchanged with the increasing loads. Walking with backpack load of 15%BW and 30%BW resulted in corresponding increase in lumbosacral force of 26.7% and 64% respectively when compared to walking without backpack load. CONCLUSION: In carrying a given packload during walking, it will give rise to a disproportionate force increase acting on the L5/S1 joint.