Cumulative electromyography of the human masseter muscle during fatiguing isometric contractions

Abstract

Six adult males performed maximum voluntary tooth clenching (MVC) for 10, 20, 30, 40 s and, after 15 min, for 40, 30, 20, 10 s. During the isometric exercises the electrical currents of the masseter muscle were sampled by integrated and cumulative surface electromyography. Subjective masseter fatigue was present after 30 and 40 s of MVC clenching, accompanied by changes in myoelectrical activity. Strength testing of the masseter muscle, before and after endurance testing, showed that the strength increased by a significant 16% following two endurance tests. This observation was explained by a post-tetanic potentiation and/or a differentiated use of motor units in the fatigued muscle. It is concluded that brief MVC isometric activity, or strength testing, is not a reliable measure of fatigue in the masseter muscle when cumulative electromyography is used. Prolonged MVC isometric activity, or progressive endurance testing, monitors reliably the onset and progression of masseter fatigue.

Isometric endurance of the human masseter muscle during consecutive bouts of tooth clenching

“…Since practically all available tnasseter motor units tnust have been recruited during 10 s of MVC activity (Destnedt & Godaux. 1979), it seetns reasonable to hypothesize that fatiguable motor units dropped out during the first endurance test (Christensen, 1984). According to Eriksson (1982), the masseter areas sarapled by EMG contained 779?…”

“…slow oxidative motor units, 12% fast glycolytic units, 8% fast oxidative-glycolytic units, and 3%' "intertnediate ATPase" units. It is hypothesized that, during the first endurance test, predominantly fast glycolytic units dropped out, possibly because peripheral chemoreceptors caused cessation of tnotor cotntnands to pain releasing and fatigued units (Molbech & Johansen, 1973;Hulten el al., 1975;Thorstensson, 1976;Asmussen, 1979;Petrofsky, 1982;Christensen, 1984).…”

Experimental Pain and Fatigue Induced by Excessive Chewing

“…The non-signi cant decrease of the MVBF in the 60-minute trial might be explained by an activity compensation in other non-affected muscle parts or muscles (43)(44)(45)(46)(47)(48)(49) or a modi cation in sensory input from muscle receptors that were affected by the increased intercuspal distance that led to stretching the bers in the jaw-closing muscles (50). Since our study included assessing bite forces, a transducer had to be placed in-between the teeth.…”

Maximal contraction force and endurance of human jaw‐closing muscles in isometric clenching

“…The endurance of the jaw-closing muscles has been studied indirectly by electromyogram (EMG) (3,4,6,8), and correlation between EMG level and bite force has been clearly documented (11,12). However, the documentation, particularly for maximal forces (as used in this study), is not so apparent.…”

“…The jaw-closing motor system has been studied extensively for its anatomic and histologic composition, and the electric activity of its muscles during rest and function (1)(2)(3)(4). Furthermore, studies have been extended to the investigation of the endurance and recovery characteristics as well as of the blood flow of these muscles (5)(6)(7)(8)(9).…”