The Effect of Isokinetic Testing Speed on the Reliability of Muscle Fatigue Indicators During a Hip Abductor-Adductor Fatigue Protocol

The aim of this study was to investigate the absolute and relative reliability of fatigue indicators calculated from peak torque and total work during isokinetic speeds of 60, 90, 120 and 180° • s-1 during a hip abductor-adductor fatigue protocol. Ten males suffering from unilateral functional ankle instability and ten male healthy controls performed five maximal concentric contractions on an isokinetic dynamometer. Following a four minute rest period subjects were instructed to perform repeated maximal concentric contractions to fatigue, which was defined as three consecutive repetitions below 50% of the maximum peak torque value. Each testing speed of 60, 90, 120 and 180° • s-1 was randomised and repeated on two separate days that were seven days apart. Peak torque and total work were calculated for each repetition and summed to compute cumulated performance for each of the testing speeds. Muscle fatigue was determined for each testing speed by the fatigue index, the percent decrease in performance and the slope of the regression equation. The most reliable fatigue determination method was the slope of the regression equation, when testing at a speed of 120° • s-1. The choice of either peak torque or total work to assess average performance during the fatigue test did not influence relative or absolute reliability. The same conclusion applied to the speed of the isokinetic dynamometer as relative and absolute reliability values were not influenced by a change in speed. It is recommended that future investigators examine and plot their data before choosing the slope of the regression equation as their fatigue indicator, as a linear model is required.