Isokinetic work-to-surface electromyographic signal energy ratios as a muscular fatigue indicator

Efficiency of muscular work is usually measured as the relationship between work load and maximum exercise duration. The present study analyzes the efficiency feature as a ratio between mechanical work (WK) and the energy (E) of the surface electromyographic signal (SEMG). This relation (WK/E(SEMG)) was compared with the most common electromyographic descriptors and its behavior was observed during muscle fatigue. A total of sixteen healthy men (26.8 +/- 4.7 yrs, 175.7 +/- 4.7 cm, and 79.2 +/- 9.4 kg) performed three sets of ten maximal concentric repetitions of dominant knee extension at 60 degrees /s on an isokinetic dynamometer, with 1 minute of rest interval between the sets. The SEMG signals were recorded during the exercises. With the view to minimize the factors other than fatigue that also influence the SEMG descriptors behavior, the only isokinetic repetition phase considered for measurements was the load range. Statistical analyses showed significant correlations between WK/E(SEMG) and the traditional electromyographic fatigue indicators.