Is spectral analysis of the surface electromyographic signal a clinically useful tool for evaluation of skeletal muscle fatigue?

Normal values for initial median frequency (IMF) of the electromyographic ( EMG) power-density spectrum must be determined before EMG spectral analysis can be used to evaluate clinically muscle fatigue. This study attempts to establish normal values in four muscles. Thirty-one healthy subjects perfor med isometric contractions of the biceps brachii, triceps, deltoid, and tib ialis anterior muscles at 50% maximum voluntary contraction. Linear regress ion analysis was used to compute the IMF and the slope of the median freque ncy as it decayed with fatigue over 45 seconds. The IMF of the tibialis ant erior (mean +/- standard deviation, 116 +/- 20 Hz) was significantly higher (p < 0.001) than that of the biceps (90 +/- 18 Hz), triceps (85 +/- 18 Hz) , and deltoid (87 +/- 15 Hz). The deltoid and tibialis anterior had the ste epest slopes. The IMF of all muscles was greater in men than in women, but gender did not affect the slope. This study attempted to establish normal v alues for IMF and slope in specific muscles. However, the range of normal v alues is so broad that it may preclude the clinical use of spectral analysi s to evaluate muscle fatigue.