Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale
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Task-dependant changes in corticomotor excitability have been described mainly in the context of grasp-oriented actions, neglecting the sensory aspects of hand function. Here, we contrasted task-dependant facilitation in small hand muscles [i.e., first dorsal interosseous (FDI) and abductor digiti minimi (ADM)] in the context of finger movements involving either discrimination or non discrimination (ND) of tactile features. Healthy young individuals (n = 16) were trained to produce rhythmic to and fro movements at the sound of metronome ticks (0.8 Hz frequency, 5 s total duration) with either the index or the little finger of the right hand. ⋯ An additional control experiment performed in a subset of the participants (n = 9) showed that MEP facilitation was substantially reduced when attention to sensations arising from finger contact with the shapes was diverted away by completion of a concurrent cognitive task (counting backward by three). These findings provide further insights into the factors influencing task-dependant changes in corticomotor excitability during hand actions. Our results highlight the importance of behavioral context and attention, in particular, in leading to further enhancement in corticomotor excitability when the finger is actively engaged in TD.
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Muscle function is altered in painful shoulder conditions. However, the influence of shoulder pain on muscle coordination of the shoulder has not been fully clarified. The aim of the present study was to examine the effect of experimentally induced shoulder pain on shoulder muscle function. ⋯ In conclusion, this study shows that acute pain both subacromially and in the supraspinatus muscle modulates coordination of the shoulder muscles during voluntary movements. During painful conditions, an increased activity was detected in the antagonist (latissimus), which support the idea that localized pain affects muscle activation in a way that protects the painful structure. Further, the changes in muscle activity following subacromial pain induction tend to expand the subacromial space and thereby decrease the load on the painful structures.
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Experimental glutamate and capsaicin-induced pain has not been described in tendon tissue despite the implications of addressing these receptors in pain management strategies. This study investigated pain induction and modulatory interactions by injecting glutamate (0.5 ml, 1 M) and capsaicin (0.5 ml, 5 microg, 33 microM) to human tendon tissue. Following the initial glutamate or capsaicin injection, a second injection of either glutamate (following capsaicin), capsaicin (following glutamate) or hypertonic saline (after both glutamate and capsaicin) was given. ⋯ The results indicate in tendon tissue a facilitation of response to capsaicin injection following glutamate injection. PPTs were only reliably reduced by capsaicin injection. These results emphasize the possible importance of peripheral glutamate receptor antagonists in pain management in musculoskeletal conditions.
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The modulation of the lower limb nociceptive withdrawal reflex elicited during late stance by a stimulus train with frequencies of 15 and 30 Hz delivered to the mid-forefoot, arch of the foot, and heel was investigated. Stimulation was delivered at four moments of the gait cycle between heel-off and toe-off. Stimulation at 15 Hz induced larger kinematic responses at the knee and hip. ⋯ The dorsiflexion response was largest when stimulating at toe-off and was larger for stimulation at 15 Hz than at 30 Hz. The muscle reflex responses were site modulated in tibialis anterior with largest responses evoked by stimulation at the arch of the foot and mid-forefoot, and phase and frequency modulated in soleus. This study presents a detailed assessment of the lower limb nociceptive reflex modulation and provides results, which might have application in the rehabilitation of the hemiparetic gait.
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Mechanisms and structures which are involved in eccentric exercise-induced delayed onset muscle soreness (DOMS) are not yet clarified. Tissue and site specificity may be important considerations in afferent sensitisation following eccentric exercise. This study investigated the nociceptive response to hypertonic sodium solution applied to fascial/epimysium tissue and mechanically sensitised sites in muscle by assessing (1) afferent recordings in animals and (2) psychophysical assessment in humans. ⋯ Fascial injection of the exercised muscle caused significantly higher pain intensity compared to all other injections. Response to deep muscle stimulation was not different between sides. This suggests that fascia rather than muscle tissue is important in DOMS associated sensitisation.