The purpose of this review is to discuss electromyography (EMG) and some of the problems and issues that are encountered during the recording and interpretation of EMG data. Recordings of electrical activity of muscles can be contaminated by interference from the electrical supply, mechanical artifacts, stimulus artifacts, and activity of other muscles. The advantages and disadvantages of surface electromyography and intramuscular EMG are compared and contrasted, and precautions to be taken when recording and interpreting these data are described. Surface electromyography is usually more susceptible to artifacts than is intramuscular EMG. It is possible, however, to make useful recordings with the surface electrodes from large superficial muscles if appropriate precautions are observed. Intramuscular electrodes, on the other hand, may be preferred for recording the activity from small peripheral muscles or muscles located deep within the body.

Introduction The main function of the masticatory muscles is to break food down into pieces small enough to be swallowed. These are strong muscles that generate very large forces across very short distances and apply themvia rigid teeth. Such large forces can easily damage the teeth and their supporting tissues, tongue, cheeks, and the joints unless they are controlled precisely and effectively. There is evidence that the masticatory forces are controlled very precisely and that these forces change from bite to bite, depending on the consistency of the bolus. However, we do not fully understand this control mechanism. Unless the details of the mechanism that controls the masticatory forces in health and disease are thoroughly understood, the diagnosis and treatment of masticatory-related dysfunctions (such as temporomandibular dysfunction) will remain at the present "symptomatic" state.The aim of this review is to discuss what is known about the control of the human masticatory system and to propose a method for standardized investigation. This review is divided into six parts. The first part discusses the activation of human jaw muscle motoneurons by the central and peripheral sources. The second part discusses the receptors that are thought to contribute to the control of human mastication. In part 3, the reflexes elicited in human subjects are discussed. In part 4, simulated chewing experiments are discussed. In part 5, recording and analyzing methods are discussed, and a new method for estimating synaptic potential in human motoneurons is introduced. Finally, in part 6, three frequently asked questions are used to discuss the issues put forward in this review.Presently, our knowledge of mastication and its control by various receptors is patchy. Most of the work in this area comes from animal species with which investigators have used widely varying reduction techniques (anesthetization, decerebration, curarization, etc.). In these preparations, when nerve pathways are the subject of the study, the nerve to be stimulated is dissected free and teased so that one or a few identified nerve fibers are stimulated. The synaptic potential that is induced by this stimulation is recorded by means of microelectrodes that are placed within the central nervous system (reviewed in Lund, 1991;Linden, 1990). It is also possible for investigators to initiate "chewing" in animal preparations, and to study the effects of various receptor systems on the development of force (Lavigne et al ., 1987;.In humans, one must establish the connections of various afferents to the motoneurons that innervate the masticatory muscles under static or dynamic conditions to begin to understand the mechanism and control of mastication. The human work is challenging, since direct recording from motoneurons is not yet possible and precise stimulation of nerves is not easily controlled. Therefore, various indirect measurements have been used for the study of synaptic potential in human subjects. In most of these studies, afferent nerves are stimul...

This study investigates whether spinal manipulation leads to neural plastic changes involving cortical drive and the H-reflex pathway. Soleus evoked V-wave, H-reflex, and M-wave recruitment curves and maximum voluntary contraction (MVC) in surface electromyography (SEMG) signals of the plantar flexors were recorded from ten subjects before and after manipulation or control intervention. Dependent measures were compared with 2-way ANOVA and Tukey's HSD as post hoc test, p was set at 0.05. Spinal manipulation resulted in increased MVC (measured with SEMG) by 59.5 ± 103.4 % (p = 0.03) and force by 16.05 ± 6.16 4 % (p = 0.0002), increased V/M max ratio by 44.97 ± 36.02 % (p = 0.006), and reduced H-reflex threshold (p = 0.018). Following the control intervention, there was a decrease in MVC (measured with SEMG) by 13.31 ± 7.27 % (p = 0.001) and force by 11.35 ± 9.99 % (p = 0.030), decreased V/M max ratio (23.45 ± 17.65 %; p = 0.03) and a decrease in the median frequency of the power spectrum (p = 0.04) of the SEMG during MVC. The H-reflex pathway is involved in the neural plastic changes that occur following spinal manipulation. The improvements in MVC following spinal manipulation are likely attributed to increased descending drive and/or modulation in afferents. Spinal manipulation appears to prevent fatigue developed during maximal contractions. Spinal manipulation appears to alter the net excitability of the low-threshold motor units, increase cortical drive, and prevent fatigue.

PurposeThe primary purpose of this study was to investigate whether a single session of spinal manipulation (SM) increases strength and cortical drive in the lower limb (soleus muscle) of elite Taekwondo athletes.MethodsSoleus-evoked V-waves, H-reflex and maximum voluntary contraction (MVC) of the plantar flexors were recorded from 11 elite Taekwondo athletes using a randomized controlled crossover design. Interventions were either SM or passive movement control. Outcomes were assessed at pre-intervention and at three post-intervention time periods (immediate post, post 30 min and post 60 min). A multifactorial repeated measures ANOVA was conducted to assess within and between group differences. Time and session were used as factors. A post hoc analysis was carried out, when an interactive effect was present. Significance was set at p ≤ 0.05.ResultsSM increased MVC force [F(3,30) = 5.95, p < 0.01], and V-waves [F(3,30) = 4.25, p = 0.01] over time compared to the control intervention. Between group differences were significant for all time periods (p < 0.05) except for the post60 force measurements (p = 0.07).ConclusionA single session of SM increased muscle strength and corticospinal excitability to ankle plantar flexor muscles in elite Taekwondo athletes. The increased MVC force lasted for 30 min and the corticospinal excitability increase persisted for at least 60 min.