Tests of muscle strength and physical function: reliability and discrimination of performance in younger and older men and older men with mobility limitations.

OBJECTIVES: To compare the reliability of muscle strength and physical function measures in younger and older men. DESIGN: Cross-sectional. SETTING: Academic research center. PARTICIPANTS: Thirty younger men, 31 older men, and 39 older men with mobility limitations. MEASUREMENTS: Test-retest measures of one repetition maximum (1 RM), unloaded and loaded 50-m walk and stair climb, and a lift-and-lower task. Reliability was assessed using intraclass correlation (ICC) analysis and the Bland-Altman method. RESULTS: Leg and chest press 1 RM measures identified significant differences between the groups, exhibited excellent test-retest reliability in younger men, older men, and older men with mobility limitations (ICCs=0.946-0.994) and minimal bias between Trials 1 and 2 (Bland-Altman=improvement of 21.1 and 1.1 N for leg and chest press, respectively). Test-retest measures of the time to walk 50 m and climb 12 steps also demonstrated excellent agreement (ICCs=0.980-0.988 and 0.942-992, respectively) and minimal bias (Bland-Altman=0.755-1.007 and 0.141-0.361 seconds faster, respectively). When a subject repeated these measures carrying a modest load, ICCs remained greater than 0.940, bias was similar, and the tests better discriminated between the groups. The lift-and-lower measure demonstrated excellent agreement (ICCs=0.925-0.947) and minimal bias (1.4-2.9 more shelves) and revealed significant differences between groups. CONCLUSION: Measures of muscle strength and physical function can be performed in younger men, older men, and older men with mobility limitations with high reliability. In future clinical trials, more-challenging measures of performance may better discriminate between higher-functioning study participants.