Objectives: Pressure algometry PA is widely used for the study of muscle sensitivity, but this method can not distinguish between the sensitivity of superficial and deep structures. Electrical ...stimulation of muscle has been suggested as a method to study muscle sensitivity. At present, it is still unknown whether electrically evoked pain thresholds PT from muscle correlate with PT determined by percutaneous PA.
Methods: Three experiments were performed to study the correlation between percutaneous pressure and electrical stimulation of the anterior tibial muscle in healthy volunteers.
In the first experiment the correlation between electrical and pressure PT In the muscle was studied. In the second experiment the correlation between visual analog scale VAS ratings after graded stimulation with PA and electrical stimulation was examined. In the third experiment electrical and pressure PT were recorded before and after cutaneous anesthesia with lidocaine.
Results: Muscle PT assessed by electrical stimulation and by PA are significantly correlated. The VAS responses produced by graded pressure stimulation are significantly correlated with VAS responses after graded electrical stimulation. Finally, the pressure PT in contrast to the electrical PT was significantly increased 45% when the skin was anesthetized with lidocaine.
Conclusions: These experiments show that graded pain responses obtained by mechanical pressure and electrical stimulation are correlated. Pressure PT, but not intramuscular electrical PT, is influenced by input from nociceptors in skin and subcutaneous tissue.
Abstract The analgesic effects of passive movements on deep-tissue pain have not been sufficiently explored in human studies. The purpose of this study was to examine the effect of passive ...physiological movements (PPMs) on deep-tissue pain sensitivity. Seventeen healthy subjects were included in this randomised crossover study. In one session an electrically driven bicycle performed 30 min PPM of the knee joint. Another session without PPM served as control. The effect of PPM on experimental muscle pain was assessed. Muscle pain was induced by i.m. injection of hypertonic saline into the tibialis anterior muscle and the pain intensity was scored on an electronic visual analogue scale (VAS). The pressure pain sensitivity was assessed by recording of pressure pain thresholds (PPTs). McGill Pain Questionnaire (MPQ) was used to describe the quality of the induced pain. Compared with the control session PPM demonstrated: (1) a reduction of the experimental muscle pain intensity (VAS area and peak) and duration (17–31%, P < 0.03), (2) lower MPQ score and a change in quality profile of experimental muscle pain (25%, P < 0.01) and (3) an increased PPT (17%, P < 0.0005). The present study demonstrated that PPM produced an immediate analgesic effect on deep-tissue pain indicating a possible involvement of neural inhibitory mechanisms.
Selective stimulation of the masseteric nerve has been shown to elicit a heteronymous H-reflex in the ipsilateral temporalis muscle during voluntary clenching. However, the relation between the ...electromyographic (EMG) activity of the temporalis muscle and the amplitude of the H-reflex has not been previously described. In the present study, the hypothesis was tested that there would be a positive relationship between the level of EMG activity and the amplitude of the H-reflex. The direct motor response (M-response) in the masseter muscle and the heteronymous H-reflex in the anterior temporalis muscle were successfully elicited by electrical stimulation of the masseteric nerve in 12 of 13 subjects. A new automatic system was used to control the on-line EMG activity and to trigger the stimulus. In a random order, two series of 20 stimuli were delivered at each of four clenching levels (0, 25, 50, and 75% of maximal voluntary contraction). The analysis showed that both the masseteric M-response and the temporalis H-reflex were reproducible within and between series. The amplitude of the temporalis H-reflex increased significantly at higher clenching levels (ANOVA: P=0.003). Clenching at 50% and 75% of the maximal voluntary contraction caused significantly larger amplitudes of the H-reflex than clenching at 25% of the maximal voluntary contraction; at rest, no H-reflex could be recorded. There was a significant correlation between the background EMG activity in the ipsilateral temporalis muscle and the amplitude of the H-reflex (Pearson: r=0.313, P=0.008). These data indicate that the heteronymous H-reflex can be reliably elicited by means of an automatic system for stimulus delivery and that the amplitude of the H-reflex is dependent on the preceding activity of the motoneuron pool.
Referral of Musculoskeletal Pain Graven-Nielsen, Thomas; Mense, Siegfried
Muscle Pain: Understanding the Mechanisms,
2010, 20100330
Book Chapter
Pain referral can pose a serious problem for the diagnosis and treatment of muscle pain because it leads to a mislocalization of the pain by the patient. Referral of pain originating in muscles can ...be elicited experimentally in a relatively high proportion of healthy subjects. Pain and tenderness can be referred to muscle from other muscles, joints, viscera, and as pain originating in the central nervous system. Clinically, muscle pain referred from other muscles has the typical characteristics of deep-tissue pain and can be elicited, e.g., by local pressure also from muscles that appear to be normal. Referral of pain from joint to muscle is frequent; it often occurs in muscles crossing the joint. Finally, pain can be experienced in muscle as an expression of central pain, i.e., pain due to lesions of the central nervous system. A prominent example of such a muscle pain is phantom limb pain. In the second part of the chapter, potential mechanisms of pain referral are discussed as well as the differences between Head zones and referred pain in the strict sense. Basically, pain referral appears to result from nociceptive information taking a wrong path in the spinal cord and reaching (somatotopically) inappropriate dorsal horn neurons. The convergence-projection theory by Ruch is still the central concept for the explanation of referred pain. It states that a given dorsal horn neuron receives synaptic connections from two separate innervation areas (convergent input), and that the neuron induces subjective pain in only one (and always the same) area, even when it is excited from the other area. The theory explains the referred pain in the skin from painful viscera. Typical examples of muscle pain referred from viscera include the chest-wall pain of cardiac infarction and the flank pain of renal calculi. A more recent version of the theory states that normally only one of the convergent connections is sufficiently effective to fire the neuron; the other elicits just subthreshold potentials in the neuron. However, the ineffective connections can become effective if there is a long-lasting lesion in the region of the ineffective connection (somatotopically inappropriate connections are opened). Thus, the nociceptive information takes a wrong course in the spinal cord and the pain is mislocalized.
It has become evident that muscle pain interferes with motor control strategies, and different patterns of interaction are reported during rest, static contractions, and dynamic conditions. A ...reorganized motor control system with functional adaptations of the muscle coordination and strategies is a key factor in musculoskeletal pain conditions; its relevance in the transition from acute pain to chronic pain is most likely underestimated. The interaction between muscle pain and motor control depends on the specific motor task. Muscle pain causes no increase in muscle activity assessed by electromyography at rest, reduces maximal voluntary contraction (MVC) levels, and shortens endurance time during submaximal contractions. Moreover, muscle pain causes an adaptive change in the coordination during dynamic exercises. In some cases, increased muscle activity reflecting reorganized muscle coordination and strategy is also a component of the functional adaptation to muscle pain. In general, the “vicious cycle” hypothesis is not supported by these findings. More relevant is an adaptive model predicting reduced agonistic muscle activity eventually advanced by changed antagonistic muscle activity. The quantitative motor control assessment procedures provide additional clinical information, and give further support for optimizing prevention procedures and treatment regimes and for musculoskeletal pain.
