Lower Limb Stiffness During a Loaded Walk and Run Over Different Surfaces.

This study quantified vertical ground reaction forces (vGRFs) and lower limb stiffness for both sexes walking and running with body-borne load over 2 surfaces. Nine males and 9 females had lower limb biomechanics quantified during a walk (1.3 m/s) and run (4.5 m/s) with (15 kg) and without (0 kg) body-borne load over a firm and soft foam surface. vGRF measures, and leg and lower limb joint stiffness were submitted to a linear mixed model. Loaded walking increased very GRF and stiffness measure (all: P < .016). Loaded running increased every GRF measure and knee stiffness (all: P < .033). The foam surface increased peak vGRF (P = .002, P = .010) and knee stiffness (P < .001, P = .004) during the walk and run, and leg (P < .001) and ankle (P = .025) stiffness during the run. Males walked with greater peak vGRF (P = .012), and stiffer hip and ankle (P = .026; P = .012), but ran with a stiffer knee on the foam (P = .041) and stiffer hip on the firm (P = .005) surface than females. Loaded walking and running may elevate injury risk by increasing vertical GRFs and lower limb stiffness. Injury risk may also increase for locomotion over a foam surface, especially for males.