This study compared the acoustic (RMS‐AMG) to electromyographic (RMS‐EMG) signal, median frequency of EMG power spectrum (Fm), and quadriceps torque during isometric fatiguing contraction (FC) and recovery. Seven subjects were tested for strength (MVC) and then, on separate days, maintained 20%, 40%, or 80% MVC to exhaustion followed by MVC testing at regular intervals. Throughout FC, RMS‐EMG significantly (P < 0.05) increased and Fm significantly (P < 0.05) decreased during all trials; RMS‐AMG significantly (P < 0.05) increased only during the 20% and 40% trials. During recovery, MVC and RMS‐EMG recovered most slowly after the 20% trial and most rapidly after the 80% trial; Fm and RMS‐AMG recovered by 90 seconds after all trials. RMS‐AMG reflects RMS‐EMG during low but not high levels of FC. Recovery of strength is most depressed following FC at lower relative levels of torque. We conclude that RMS‐AMG behaves differently than RMS‐EMG, torque, and Fm during FC and recovery. © 1993 John Wiley & Sons, Inc.
- muscle sounds
- quadriceps femoris