The relative importance of strength and balance in chair rise by functionally impaired older individuals

OBJECTIVE: The ability to stand independently and safely from the seated position is essential for independent function. This investigation determined the relative contributions of measures of lower extremity strength and measures of balance control in explaining the performance characteristics of sitting-to-standing. Variables analyzed included those related to success of the activity (e.g., time to rise, lowest chair height) and to biomechanical characteristics of performance (e.g., how fast specific body segments moved). SETTING: Durham Veteran's Affairs Medical Center motion analysis laboratory. DESIGN: Cross-sectional correlational study. PARTICIPANTS: Fifty-eight men and women aged 66 to 96 (mean = 77) with functional limitations. MEASUREMENTS: Predictor variables were lower extremity strength (isometric) and balance (functional reach and sway). The outcome variable, chair rise performance, was quantified by: lowest successful chair height (chairs at 33 to 58 cm); time to rise; maximum hip flexion angular velocity; and the maximum horizontal and vertical velocities of the motion of the body center of mass (COM). Covariates were lower extremity range of motion and sensory status. RESULTS: With bivariate analysis, lower extremity strength demonstrated relationships with the lowest chair height (r = -0.639) and maximum vertical velocity of the COM (r = .389); functional reach was associated with three variables (lowest chair height r = .374; time to rise r = .297; and maximum horizontal velocity of the COM r = .251). Using a multivariate regression analysis (including lower extremity strength, functional reach, sensory loss, and lower extremity range of motion), the model accounted for 47% of the variance in lowest chair height; lower extremity strength was the only significant predictor (P < .001). The model also accounted for 20% of the variance in maximum horizontal velocity of the COM; lower extremity strength was a significant predictor (P = .006). CONCLUSIONS: Lower extremity strength and balance control both play a role in performance of chair rise; lower extremity strength is the stronger predictor of success for functionally impaired older adults.