RELIABILITY OF MEASUREMENTS OF BODY CENTER-OF-MASS MOMENTUM DURING SIT-TO-STAND IN HEALTHY-ADULTS

Background and Purpose. The purpose of this study was to determine the reliability of measurements of momentum of the body's center of mass (CM) during a sit-to-stand (STS) transfer in healthy adults. Subjects. Nineteen healthy adults aged 25 to 38 years (($) over bar X=31.7, SD= 4.2) participated. Methods. Horizontal and vertical components of CM m omentum were computed for STS transfers made at three movement speeds (fast, natural, and slow) with the aid of a motion analysis system. Tw o force platforms detected the time when the subject lost contact with the chair and the propulsive and braking impulses in the horizontal a nd vertical directions. Separate intraclass correlation coefficients ( ICCs) were calculated for three temporal variables (time to peak horiz ontal and vertical momentum and time to when the subject lost contact with the chair) and two magnitude variables (peak horizontal and verti cal momentum). Results. The ICCs for magnitude variables were greater than or equal to .81 for an speeds of movement. The ICCs for temporal variables ranged from .28 for fast movements to .75 for slow movements . Conclusion and Discussion. Measurement of peak vertical and horizont al momentum magnitudes is highly reproducible during STS transfers. Me asurement of temporal variables exhibits a range of reliability estima tes. Implications include consideration of the speed at which STS tran sfer is performed and its effect on reliability estimates and the pote ntial differences between reliability estimates for magnitude measurem ents versus temporal measurements.