Tests of Muscle Strength and Physical Function: Reliability and Discrimination of Performance in Younger and Older Men and Older Men with Mobility Limitations

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Abstract
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.