The ability to perform voluntary muscle contractions with minimum fluctuations in torque while matching a given torque level represents a measure of how accurately and smoothly a subject can control the torque developed by a particular muscle or muscle group. The precision of these movements is controlled by the central nervous system on the basis of information from sensory inputs applied to the visual, vestibular and somatosensory systems. So, the investigation of how the nervous system controls movements has been studied in several ways, for example by applying sensory inputs in addition to those occurring naturally. More specifically, noise-based sensory stimulations have been employed so as to enhance somatosensation and hence improve the control of postural sway. One of the aims of this work is to investigate the effects of electrical noise stimulation (applied to the leg muscles and to the foot soles) on plantarflexion torque variability (voluntarily maintained), during two different tasks, one being performed with a constant torque level against a rigid restraint (force task, FT) and the other with a constant angle while supporting an inertial load (position task, PT). The second aim is to evaluate, by the conditioning of the H reflex with stimulation on the common peroneal nerve, the inhibitory spinal circuits (more specifically, the levels of reciprocal inhibition and presynaptic inhibition) associated with the muscles responsible for plantarflexion torque maintenance during the two different tasks (FT and PT). Besides allowing a better understanding on the neurophysiology of neuromuscular control, the results with healthy subjects may indicate the potential for the clinical usage of noise-based stimulations to enhance neuromuscular control in a population with sensory-motor impairments.
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