Whinton, A., Aubry, R., Power, G.A. & Burr, J.F. (2016)
Purpose: The purpose of this study was to validate and assess the reliability of a custom-built isokinetic dynamometer. Methods: Twelve healthy, male participants (27 ± 4.5 yrs, 80.6 ± 4.2 kg, 179.8 ± 2.2 cm) performed concentric knee extension on 1) a dynamometer constructed using a leg extension machine with a computer controlled cable resistance machine (1080 Quantum) and 2) a commercially available dynamometer (Cybex, Humac Norm) to determine reproducibility of the 1080 Quantum. Validity and reliability was assessed by comparing maximal effort consecutive knee contractions through 90° flexion on each leg using the 1080 Quantum at a linear velocity of 0.5 m×s-1 and on the Cybex at an angular velocity 180 °×s-1, performed twice on the 1080 Quantum and once on the Cybex. Peak power (W), mean power (W), and fatigue rate (%) ((avg first 5 contractions - avg last 5 contractions)/avg frist 5 contractions)) x 100) were quantified. Student´s paired t-test, coefficient of variation (CV) and intra-class correlation coefficient (ICC) were used to examine reproducibility within and between devices. Results: Significant, yet consistent, differences were demonstrated for peak power between dynamometers (Quantum: 706 ± 176 W, Cyber: 439 ± 101 W, p < 0.0001); however the ICC (0.72) indicated a reasonably strong association. Repeated tests on the 1080 Quantum revealed very high reliability (ICC = 0.93), with no observed differences in peak power between tests (p < 0.85). The CV´s for mean power were 9.4% and 13.4% for the 1080 Quantum and Cybex, respectively. Fatigue rates were similar between repeated trials on the 1080 Quantum (test 1: 14.5 ± 4.5 %, test 2: 13.8 ± 4.3%, p < 0.53) but differed between devices (1080 Quantum: 14.1 ± 4.3%, Cybex: 5.2 ± 5.9%, p < 0.003). Conclusion: Although, absolute power outputs differed between devices, the off-set was consistent within subjects across devices and likely related to the movement pattern and lever arm differences. As such, the 1080 Quantum independently represents a valuable and reliable tool for executing and reporting maximal knee contraction power.