PURPOSE:Knowledge of hip biomechanics during locomotion is necessary for designing optimal rehabilitation programs for hip-related conditions. The purpose of this study was to: 1) determine how lower-limb muscle contributions to the hip contact force (HCF) differed between walking and running; and 2) compare both absolute and per-unit-distance (PUD) loads at the hip during walking and running. METHODS:Kinematic and ground reaction force data were captured from eight healthy participants during overground walking and running at various steady-state speeds (walking: 1.50 ± 0.11 m·s and 1.98 ± 0.03 m·s; running: 2.15 ± 0.18 m·s and 3.47 ± 0.11 m·s). A three-dimensional musculoskeletal model was used to calculate the HCF as well as lower-limb muscular contributions to the HCF in each direction (posterior-anterior; inferior-superior; lateral-medial). The impulse of the resultant HCF was calculated as well as the PUD impulse (BW·s·m) and PUD force (BW·m). RESULTS:For both walking and running, HCF magnitude was greater during stance than swing and was largest in the inferior-superior direction and smallest in the posterior-anterior direction. Gluteus medius, iliopsoas, and gluteus maximus generated the largest contributions to the HCF during stance, whereas iliopsoas and hamstrings generated the largest contributions during swing. When comparing all locomotion conditions, the impulse of the resultant HCF was smallest for running at 2.15 m·s with an average magnitude of 2.14 ± 0.31 BW·s, whereas the PUD impulse and force were smallest for running at 3.47 m·s with average magnitudes of 0.95 ± 0.18 BW·s·m and 1.25 ± 0.24 BW·m, respectively. CONCLUSIONS:Hip PUD loads were lower for running at 3.47 m·s compared with all other locomotion conditions because of a greater distance travelled per stride (PUD impulse) or a shorter stride duration combined with a greater distance travelled per stride (PUD force).