Effect Of Age And Seat-height On Muscle Contributions To Center Of Mass Acceleration During Sit-to-stand

PURPOSE: The purpose of this study was to calculate muscle forces and identify their contributions to accelerating the center-of-mass (COM) during a sit-to-stand (STS) task from three different seat heights in young and older adults. METHODS: Fifteen healthy young and fourteen healthy older adults participated in this study. Each participant performed five STS trials from heights of 30 cm (low), 45 cm (middle), and 60 cm (high). Motion capture, force plate, and electromyography data were recorded. Muscle forces and their contributions to acceleration of COM were calculated via computed muscle control and induced acceleration analysis, respectively. Statistical Parametric Mapping was used to investigate age and seat-height related differences in muscle forces and muscle specific contributions to COM acceleration. RESULTS: At the low seat-height, muscle forces of vastus lateralis (p = 0.003), vastus intermedius (p = 0.009), and vastus medialis (p = 0.002) in older adults were significantly greater than those in young adults during 30-50% of the STS motion. The contribution of muscle forces to vertical acceleration of the center of mass was not significantly different between young and older adults during the STS task across three seat heights. However, the muscle-specific contribution to the anteroposterior acceleration from the vastus lateralis (p = 0.001), vastus intermedius (p = 0.015), and vastus medialis (p = 0.018) in older adults were significantly greater during approximately 30-50% of the STS motion at the low seat-height compared to young adults. CONCLUSIONS: Older adults produced greater quadriceps muscle forces than young adults during STS task at the low seat-height. This difference resulted in greater acceleration of COM in the anterior direction. Given that control of COM acceleration in the anteroposterior direction is related to the control of balance during STS, the greater quadriceps muscle forces produced by older adults may be compensatory strategy to maintain their balance during sit-to-stand with low height chair. Further studies are warranted to determine whether the greater contribution of the quadriceps to anterior acceleration of COM among older adults correlates with fall risk. National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. RS-2022-00165979) and BK21 FOUR (Fostering Outstanding Universities for Research) (No. :5199990914048)