Frequency of acoustic myography during isometric contraction of fresh and fatigued muscle and during dynamic contractions.

The frequency of the acoustic myographic (AMG) signal was examined during fresh and fatigued isometric contractions of quadriceps and during dynamic contractions of biceps brachii (BB) in healthy subjects. Recordings were obtained from quadriceps over a range of forces between 10% and 100% maximal voluntary contraction prior to, and 15 minutes after, a fatiguing exercise. Recordings from BB were obtained over a range of submaximal forces (0-8.5 kg) during concentric and eccentric contractions. The mean power frequency (MPF) of the AMG signal was analyzed during each of these contractions by fast-Fourier transform (FFT). The MPF was not significantly different (P > 0.05) during fresh and fatigued contractions of quadriceps and increased quadratically with force in both states (r = 0.81, fresh; r = 0.77, fatigued). During concentric contractions of BB the MPF initially increased with force, but then decreased at the heavier loads (> 5.5 kg). The MPF of eccentric contractions did not significantly (P > 0.05) alter with force. The AMG MPF was within a similar low frequency range for both muscles, during different types of contraction, and was unaltered with fatigue.