A contracting muscle generates a pressure wave due to the lateral dimensional change in active muscle fibers, which is detectable with vibration transducers such as accelerometers and microphones on the body surface overlying the muscle. The recording of this pressure wave is referred to as the mechanomyogram (MMG). The MMG is the mechanical counterpart of myoelectrical activity. The MMG amplitude, when elicited by electrical stimulation, increases with the intensity of stimulation, although at high stimulation rates a reduction in the MMG amplitude occurs due to mechanical fusing of the motor unit activity. These properties indicate that both the number of recruited motor units and their firing rate influence the MMG. It is possible that the MMG is a useful way of indicating force, evaluating muscle fatigue, controlling prostheses, determining muscle contractile properties, and estimating the motor unit activation strategy. The present review article focuses on the introduction of the MMG in clinical examinations and in diagnosing neuromuscular diseases. The time and frequency domain parameters of the MMG during voluntary muscle action and electrical stimulation have been used in previous clinical studies. However, only a small number of clinical MMG studies and papers, i. e., less than several score have been published in the relevant international journals.
