Effect of forefoot strike and toe-out running on knee contact forces: a musculoskeletal modelling-based study

Knee osteoarthritis (OA) is a common degenerative joint condition with significant public health implications. Modifying running biomechanics is a potential strategy to reduce knee joint loading and support long-term maintenance of physical activity in individuals with knee OA. This study investigated the effects of running modifications on knee contact force (KCF) between natural running, forefoot striking (FFS), and toe-out running. Ten healthy participants performed three trials of 20-m overground running for each condition. KCF were estimated using an OpenSim-based musculoskeletal model, and differences across conditions were evaluated using a one-way repeated measures ANOVA. In early stance, toe-out running exhibited higher medial-lateral KCF compared to both natural running (p = 0.017, Cohen's d = 0.92) and FFS (p = 0.003, Cohen's d = 1.28). In late stance, both FFS (p = 0.039, Cohen's d = 0.76) and toe-out (p = 0.011, Cohen's d = 1.01) running exhibited increased medial-lateral KCF relative to natural running. Additionally, FFS generated significantly higher vertical KCF than both natural (p < 0.001, Cohen's d = 2.32) and toe-out running (p < 0.001, Cohen's d = 1.70). Running modifications involving toe-out or FFS resulted in increased KCF, particularly in the medial-lateral direction. These findings suggest such modifications may not effectively reduce joint loading and should be approached with caution in individuals with knee OA.