Self-report and physical performance measures of physical function in hip osteoarthritis: relationship to isometric quadriceps torque development.

OBJECTIVE: Quadriceps strength (knee extensor torque) is an important correlate of physical function in individuals with hip osteoarthritis (OA). However, it remains unclear whether the ability to rapidly generate quadriceps torque in the early phase of muscle contraction (maximal rate of torque development [MRTD]) is also associated with physical function. The purpose of this study was to quantify the independent impact of quadriceps strength and quadriceps MRTD on self-report and physical performance measures of physical function in community-dwelling adults with hip OA.
METHODS: Ninety-two adults with radiographically confirmed symptomatic hip OA (mean age 62 years) participated. Unilateral isometric quadriceps strength and MRTD were measured using a dynamometer. Self-report measure of physical function was assessed by the Short Form 36 (SF-36) questionnaire, and physical performance was assessed by the timed stair and step tests.
RESULTS: In the hierarchical regression models, high maximal quadriceps strength and high quadriceps MRTD uniquely covaried with high SF-36 physical function scores after accounting for demographic, anthropometric, and pain measures. For the timed stair test, all else being equal, in 2 participants with low but identical levels of quadriceps strength, the one with a higher MRTD had better stair-climbing function. For the step test, quadriceps MRTD was not associated with step test performance over and above that of quadriceps strength.
CONCLUSION: In individuals with hip OA, maximal quadriceps strength and quadriceps MRTD positively impact self-report and physical performance measures of physical function. These findings are of importance in developing intervention strategies, but they call for further study.