Speed and Terrain Impact Ground Reaction Forces During Load Carriage

Load carriage leads to larger, faster vertical ground reaction forces (GRFs), and greater risk of musculoskeletal injury. Although increased lower limb flexion can help dissipate the vertical GRF, reducing injury risk, it is unclear if terrain affects limb flexion and vertical GRFs during load carriage. This study quantified lower limb biomechanics as participants walked, jogged and ran with heavy body borne load over different terrain. We hypothesize that participants will decrease lower limb flexion, but increase peak vertical GRFs as speed increases, but these changes will vary with terrain. Each participant walked (1.3 m/s), jogged (3.0 m/s) and ran (4.5 m/s) with body borne load (15 kg) over a rocky, firm, soft, and flat terrain. During each locomotor task, peak vertical GRF and range of hip, knee and ankle motion (ROM) were calculated, and submitted to statistical analysis. Significant speed by surface interactions were evident for peak vertical GRF (p < 0.001), and ankle and knee ROM (p=0.030 and p < 0.001). Speed impacted peak vertical GRF, and ankle and knee ROM (all: p < 0.001), where GRF and ankle were larger, but knee motion smaller during the run. Surface impacted peak vertical GRF and ankle ROM (p < 0.001 and p=0.008). Unexpectedly, participants decreased peak vertical GRF on the rocky compared to all other surfaces. Through the use of this study, training programs can be adapted to help athletes and military personnel decrease their risk of injury while training.