The Reliability and Validity of Measuring Devices for Measuring Mechanical Power

Abstract

The Reliability and Validity of Measuring Devices for Measuring Mechanical Power The primary purpose of this paper is to validate a 3-D motion capture system as a reliable and valid measurement tool to be used in the practical setting for measuring bar velocity and mechanical power output. One resistance-trained, male college student participated in this study, performing ten sets of one repetition at loads of 30, 40, 50, 60, 70, and 80% of his 1 repetition maximum (1 RM) for the barbell back squat exercise. Each repetition was simultaneously recorded with a 3-D camera (EliteForm PowerTracker; EliteForm, Lincoln, Nebraska), a tether based position transducer (gold standard), and a tether-based external dynamometer. Power values were derived using the bar velocity and the system mass (external load + 88% of body mass). Both Mean and Peak Velocity and Mean and Peak Power values were used to compare the measurement devices. In addition to linear regression, and correlation data, Bland-Altman plots (Tukey mean difference analyses) were created to measure agreement in the relative difference of values from each system. There were significant correlations (r .80) between all 3 methods, but were highest in mean velocity and peak velocity. Mean velocity and mean power are shown to be within the limits of agreement when comparing the 3-D camera system and LPT, while peak velocity and peak power are outside of the limits of agreement. However, a comparison of 3-D camera system and external dynamometer, shows that all 4 variables were within 95% limits of agreement. Overall, the technology in question offers a reliable means of assessing velocity and power measurements in the practical setting.