Empirical Validation of a Streamlined 3-Repetition Sit-to-Stand Protocol Using MAI Motion

MAI Motion is a motion capture system designed to assess lower-limb biomechanics during functional movements like the sit-to-stand (STS) test. Determining how many repetitions are needed to obtain reliable measurements is critical for balancing data quality and participant burden. This study evaluates whether three repetitions (3x) of STS provide sufficiently reliable data compared to five repetitions (5x). 3D videos of participants (n=10) performing 5x STS movements were captured using MAI Motion. Primary measurements were the mean values of each joint angle and the coefficient of variation (CV). Statistical comparisons (paired t-tests or non-parametric equivalents) determined differences in mean values or CV existed between 3x and 5x. Analysis revealed minimal differences in mean angles between 3x and 5x. Variability, assessed via CV, showed no clinically meaningful differences. Although ankle angle, knee and hip abduction had higher CV values than other metrics, 3x and 5x performed similarly. Participants reported that 3x required less effort than 5x, implying practical advantage for clinical or research settings. These findings validate that a 3x STS captures biomechanical data comparable to a 5x protocol using the MAI Motion system. Reducing repetitions can lessen participant fatigue while preserving measurement reliability, making 3x a pragmatic standard for most populations.