Clinical Application of Silent Period for the Evaluation of Neuro-Muscular Function in the Field of the Sports Medicine and Rehabilitation

Abstract

A transient suppression of muscle activation was produced by electric stimulation to the innervating nerve during continued effort. This period of electrical inactivity, designated the mixed nerve silent period, results from several physiologic mechanisms (Kimura, 2001). On the other hand, the silent period during tonic muscle contraction demonstrated on electromyography is due to the rapid voluntary movement during tonic and mild muscle contraction (Ikai, 1955) and is elicited by cutaneous electrical stimulation of supplying nerve during muscle contraction (Higgins & Lieberman, 1968). In many previous studies about silent period, it was generally classified into three categories: (1) the quiet period of bursting wave activity on electromyography, recorded before the rapid motion in response to visual, auditory, light and/or sound stimulation (Yabe, 1976); (2) a transient suppression of muscle activation following electric stimulation of the mixed nerve innervating that muscle during continued effort (Kimura, 2001); (3) a pause of the muscle activity following the motor potential elicited by cortical magnetic stimulation during voluntary target muscle contraction (Calancie et al, 1987). In this study, we used the second category, according to which the silent period consists of several waves, including M wave, F wave and Long Latency Reflex (LLR). The silent period in this article, which classified in the second category, is the duration of the inhibitory period of muscle contraction detected on surface electromyography, which is due to electrical stimulation at the innervating nerve during tonic muscle contraction (Figure 1). We have considered that the silent period of lower extremity is the total circuit time from the peripheral nerve stimulus point to the central nervous system (i.e., brainstem or motor cortex), because the M wave, F wave and LLR are included in the silent period on evoked electromyography. M wave is affected by the conductive condition of peripheral nerve and the muscle state (i.e. rest or contraction, length, volume and so on) (Fuglevand et al, 1993, Cupido et al, 1992, Behm & St-Pierre, 1997). F wave is influenced by the excitability of the spinal motor neuron function (Suzuki et al, 1993). LLR in the lower extremities is affected by