Added Load Alters Ankle And Knee Joint Moments During Stair Descent

Abstract

INTRODUCTION: Combat forces perform a number of tasks with a rigid load added to the trunk including walking, running and stair ascent and descent. Though a number of studies have investigated the effect of added loads on joint biomechanics during over ground and treadmill walking, less focus has been applied to negotiating stairs. Changes in lower extremity biomechanics during stair descent may be associated with excessive joint loading. PURPOSE: to quantify changes in joint kinetics when descending stairs with increasing loads. METHODS: Ten healthy adults (age: 18 - 30) performed 5 stair descent trials in each of 5 loading conditions: body weight (BW), BW+5%, BW+10%, BW+15%, and BW+20%. Mass was added using a modular vest and metal plates. An 18-camera motion capture system (240 Hz) and embedded force platform (1200 Hz) was used to collect kinematics and ground reaction forces simultaneously. Commercial biomechanical software was used to calculate ankle, knee and hip joint moments during the stance phase of second step of a five-step stairway. Univariate ANOVAs with Tukey’s post-hoc tests were used to compare peak ankle, knee and hip joint moments from each loaded condition. RESULTS: Ankle plantarflexion moments increased at BW+15% and BW+20% (Table 1). Hip and knee extension moments were not altered with added load. DISCUSSIONS/CONCLUSION: The ankle joint is the primary contributor to increased lower extremity joint moments only in response to added load at or exceeding +15% BW during stair descent. Interestingly, no changes in peak joint moments were observed at the knee and hip joint, suggesting that neither joint is responsible for increased energy absorption in response to added load during stair descent. Further research may seek to investigate the effects of fatigue on joint kinetics during stair descent.