EFFECTS OF VARYING BACKPACK LOADS ON PEAK FORCES IN THE LUMBOSACRAL SPINE DURING WALKING

Objective. To compare the differences in lumbosacral spine forces unde r varying backpack loads. Design. A biomechanical model was used to de termine the changes in peak forces in the L5/S1 joint with increasing backpack loads during level walking. Background. Most studies involvin g varying external backpack loads have been concerned mainly with kine matic and physiological measurements. To the author's knowledge, there has been no investigation of the change in peak forces in the lumbosa cral 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 loadin g conditions were studied, that is walking with no load, with 15% BW a nd with 30% BW. Results. It was observed that all the ten subjects whi le walking with heavier backpack load adopted a compensatory trunk fle xion posture. However, kinematic gait parameters such as walking speed and stride length remained unchanged with the increasing loads. Walki ng with backpack load of 15% BW and 30% BW resulted in corresponding i ncrease in lumbosacral force of 26.7% and 64% respectively when compar ed to walking without backpack load. Conclusion. In carrying a given p ackload during walking, it will give rise to a disproportionate force increase acting on the L5/S1 joint. Relevance In the prevention of low back injury, the determination of carrying limits for individuals sho uld consider the disproportionate increase in peak lumbosacral forces that arise for a given backpack load. (C) 1998 Elsevier Science Ltd. A ll rights reserved.