AMG and EMG spectra for mixed muscle fiber types

Summary form only given. The purpose of this study was to determine the effects of localized fatigue on the spectrum of the electromyograph (EMG) and acoustic myogram (AMG), which is largely subsonic in the human vastus lateralis (VL) muscle. Fourteen healthy, undergraduate men and women were tested for a maximum voluntary contraction (MVC) of the quadriceps group. On a subsequent day, fatigue was defined as the time when subjects could not sustain a contraction equal to 75% of MVC. EMG and AMG records were taken when the subjects reached 75% of MVC and at the onset of fatigue. Fast Fourier transform (FFT) using an accelerometer and bipolar surface electrodes was used for AMG and EMG measurements, respectively. Statistical analysis of peak decibel means every 10 Hz showed that: (1) AMG has a lower frequency band than the EMG and is distinct from it; (2) the decibel level significantly increased at 10 Hz (p<0.05) in the AMG but decreased at 80 Hz (p<0.01) when the VL muscle fatigued; and (3) the decibel level significantly increased at 20 Hz and 10 Hz (p <0.05) in the EMG when the muscle fatigued