Coordination of strength exertion during the chair-rise movement in very old people.

BACKGROUND Changes in performance of standing up from a chair have been related to measures of strength or power. However, the sit-to-stand (STS) transfer requires that the individual exerts forces with appropriate magnitude and timing. These coordinative aspects have received less attention. This study aims to analyze differences in STS performance in older people based on measures that are derived from ground reaction forces (GRFs) during STS transfer. METHODS One hundred thirty-five participants (84.5% women; mean age 82.5 years) stood up from a chair as fast as possible. Time of stabilization after reaching an upright position, power, maximum vertical GRF, increase of vertical GRF, overshoot of vertical GRF over body weight, and left-right difference of GRF were measured by a force plate under each foot. To explain variance of total time to stand up, these variables were used as independent variables in a linear regression model. RESULTS Eighty-one percent of variance of total time to stand up was explained by the independent variables. The strongest predictor of total time was time of stabilization (F = 459.4). Another model of linear regression explained 37% of variance of time to reach an upright position, with increase of GRF as the strongest predictor (F = 38.3). Influence of maximum vertical GRF was weak in both models. CONCLUSIONS Variables related to coordination of strength, measured during STS transfer, were able to explain a high proportion of variance of time to rise from a chair. Stabilization after reaching an upright position seems to be a parameter worth further investigation.