Assessment of the reliability of high-intensity quadriceps femoris muscle fatigue

Objective: The purpose of this study was to evaluate test-retest reliabilit y of two different measures of isokinetic quadriceps muscle fatigue, Method s: Subjects for this study included 16 healthy, college age volunteers. Eac h subject performed 30 maximal, concentric repetitions on the Biodex System II Isokinetic Dynamometer at a preset angular velocity of 180 degrees .s(- 1) for both the dominant and nondominant legs. Quadriceps work was evaluate d between an angular range of 10 degrees and 60 degrees of flexion for each repetition. Quadriceps muscle fatigue was calculated through a fatigue ind ex (work performed last 5 repetitions/work performed first five repetitions x 100) and the linear slope (beta) across the 30 repetitions. The subjects ; participated in two test sessions separated by one to two weeks. Intracla ss correlation coefficients (ICC) and standard errors of measurements (SEM) were calculated for each fatigue measure on both legs. Results: The findin gs demonstrated moderate to high ICCs for the nondominant leg (ICC = 0.78-0 .92) and high ICCs for the slope and y-intercept for the dominant leg (ICC = 0.82 and 0.89, respectively). The fatigue index for the dominant leg was found to be low (ICC = 0.26). Conclusions: The findings of this study sugge st that the quantification of muscle fatigue during high-intensity, short-t erm exercise is more reliably described by the slope, which is related to t he magnitude of force output.