Background: Sit-to-stand movements are a necessary part of daily life, and excessive\nmechanical stress on the articular cartilage has been reported to encourage the progression\nof osteoarthritis. Although a change in hip joint angle at seat-off may affect\nhip joint contact force during a sit-to-stand movement, the effect is unclear. This study\naimed to examine the effect of the hip joint angle at seat-off on the hip joint contact\nforce during a sit-to-stand movement by using a computer simulation.\nMethods: A musculoskeletal model was created for the computer simulation, and\neight muscles were attached to each lower limb. Various sit-to-stand movements\nwere generated using parameters (e.g., seat height and time from seat-off to standing\nposture) reported by previous studies. The hip joint contact force for each sit-to-stand\nmovement was calculated. Furthermore, the effect of the hip joint angle at seat-off on\nthe hip joint contact force during the sit-to-stand movement was examined. In this\nstudy, as the changes to the musculoskeletal model parameters affect the hip joint\ncontact force, a sensitivity analysis was conducted.\nResults and conclusions: The hip joint contact force during the sit-to-stand movement\nincreased approximately linearly as the hip flexion angle at the seat-off increased.\nMoreover, the normal sit-to-stand movement and the sit-to-stand movement yielding\na minimum hip joint contact force were approximately equivalent. The effect of the\nchanges to the musculoskeletal model parameters on the main findings of this study\nwas minimal. Thus, the main findings are robust and may help prevent the progression\nof hip osteoarthritis by decreasing mechanical stress, which will be explored in future\nstudies.
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