Abstract
Isotonic testing and measures of rapid power production are emerging as functionally relevant test methods for detection of muscle aging. Our objective was to assess reliability of rapid velocity and power measures in older adults using the isotonic mode of an isokinetic dynamometer. Sixty-three participants (aged 65 to 82 years) underwent a test-retest protocol with one week time interval. Isotonic knee extension tests were performed at four different loads: 0%, 25%, 50% and 75% of maximal isometric strength. Peak velocity (pV) and power (pP) were determined as the highest values of the velocity and power curve. Rate of velocity (RVD) and power development (RPD) were calculated as the linear slopes of the velocity- and power-time curve. Relative and absolute measures of test-retest reliability were analyzed using intraclass correlation coefficients (ICC), standard error of measurement (SEM) and Bland-Altman analyses. Overall, reliability was high for pV, pP, RVD and RPD at 0%, 25% and 50% load (ICC: .85 - .98, SEM: 3% - 10%). A trend for increased reliability at lower loads seemed apparent. The tests at 75% load led to range of motion failure and should be avoided. In addition, results demonstrated that caution is advised when interpreting early phase results (first 50ms). To conclude, our results support the use of the isotonic mode of an isokinetic dynamometer for testing rapid power and velocity characteristics in older adults, which is of high clinical relevance given that these muscle characteristics are emerging as the primary outcomes for preventive and rehabilitative interventions in aging research.
Highlights
In geriatrics and aging research, measures of muscle function are commonly used to screen for an age-related loss of muscle strength and power and to evaluate the effectiveness of exercise interventions [1, 2]
Isotonic training and testing has been performed on common weight stack machines for years, little is known about the isotonic mode of an isokinetic dynamometer, which allows for better standardization, accurate continuous measurement of torque and velocity in a predetermined range of motion and reduced muscle soreness [17]
Mean and standard deviation (SD) of the test and retest session for peak velocity, peak power, rate of velocity development until pV (RVD) and at intervals of 50ms (RVD0–50, RVD50–100, RVD100–150) and rate of power development until pP (RPD) and at intervals of 50ms (RPD0–50, RPD50–100, RPD100–150) measured during the isotonic tests at 0%, 25% and 50% of maximal isometric strength
Summary
In geriatrics and aging research, measures of muscle function are commonly used to screen for an age-related loss of muscle strength and power and to evaluate the effectiveness of exercise interventions [1, 2]. In addition to the isokinetic mode, an isokinetic dynamometer can operate in an isometric and an isotonic mode [1, 15] In the former, maximal strength is produced in a predetermined position without limb movement. Isotonic tests can be performed at a certain percentage of the isometric maximum, allowing for power production across the entire power-load relationship These tests can be considered as relative tests of a subject’s ability (i.e. maximal isometric strength) to generate power. Isotonic training and testing has been performed on common weight stack machines for years, little is known about the isotonic mode of an isokinetic dynamometer, which allows for better standardization, accurate continuous measurement of torque and velocity in a predetermined range of motion and reduced muscle soreness (i.e. concentric only) [17]. Little is known about the reliability of isotonic measures of knee extensor function, in particular in older adults
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