Reliability Of Muscle Power And Functional Performance In Healthy, Older Women

Abstract

Functional performance measures in older adults are commonly used in studies investigating age-related declines in mobility. Surprisingly, there is a lack of literature on the clinimetric properties associated with these tests, especially in healthy, older adults. In addition, reliability of tests is commonly measured over 1-2 weeks, and does not address the question of longer-term reliability that might be more relevant for a typical training study. PURPOSE: The purpose of this study was to assess the longer-term reliability (over 9 weeks and 15 weeks) of an isotonic muscle power test (using an isokinetic dynamometer) and commonly-used functional measures (Short Physical Performance Battery, maximal gait, 30s chair stand test, stair climbing, and the 400-meter walk) in healthy, older women. METHODS: Participants were older women (n = 18) who were healthy and untrained (Age = 73.3 ± 3.4 years, Height = 159.6 ± 7.7 cm, Weight = 69.5 ± 12.7 kg, BMI = 27.3 ± 4.8). Test-retest measures (muscle power and function) took place at baseline, week 9, and week 15. Intraclass correlation coefficients (ICC) and the coefficient of variation of the typical error (CV) are reported for all time point comparisons. RESULTS: ICCs ranged from 0.83-0.97 for muscle power, and 0.64-0.93 for functional performance, indicating moderate to excellent reliability. CVs for upper-leg muscle power ranged from 5.7 - 10.5%, and lower-leg muscle power ranged from 9.9 - 20.0%, while CVs for functional tests ranged from 1.9 - 14.9%. For function, the stair-climb power test demonstrated the greatest reliability from baseline to week 15, with the CV = 8.94% and ICC = 0.94 (CI = 0.82-0.98). There were no changes in mean values for tests over time, with the exception of the chair stands which improved significantly from baseline to week 15 (p < 0.05). Although the chair stands were significantly different, these changes were smaller than what has previously been identified as clinically meaningful (eg. < 3.3 chair stands for the 30s chair stand test). CONCLUSIONS: Muscle power and functional tests demonstrated consistency over durations typically used in exercise studies. Conducting these tests under standardized conditions should enable researchers to confidently describe the impact of exercise interventions on muscle power and function in this population.