Mechanomyographic responses in quadriceps muscles during fatigue by continuous cycle exercise

The present study examined whether the mechanomyogram (MMG) could assess the fatigue-related changes in muscle mechanical properties during cycle exercise. In eight male subjects, the MMG signals were measured in vastus lateralis and rectus femoris by electret condenser microphones. It was found that the integrated MMG (iMMG) showed non linear increase against workload during continuous, incremental cycle exercise and the onset of abrupt changes in iMMG coincided with the ventilatory threshold (VT). Specifically, iMMG in vastus lateralis showed a significant decrement in the rate of increase against workload above VT, reflecting the fatigue-induced impairment of contractile properties of the fibers of active motor units. These results suggest that the MMG measured by electret condenser microphone could be practically used to retrieve the fatigue-related changes in muscle mechanical properties during cycle exercise.