Empirical Validation of a Streamlined Three-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 reliable data compared to five repetitions (5x). Three-dimensional videos of participants (n = 20) 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 (including one way ANOVA followed by paired t-tests or non-parametric equivalents) determined whether differences in mean (DiM) values or CV existed between 3x and 5x. The analysis revealed minimal DiM 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 the other metrics, 3x and 5x performed similarly. Participants reported that 3x required less effort than 5x, underscoring its potential for clinical application. These findings demonstrate that the MAI Motion system captures comparable biomechanical data to the 5x STS protocol when using a 3x approach. This supports the adoption of 3x as a practical alternative, reducing participant burden.