Muscle Activation of the Lower Limb in Response to a Medio-lateral Imbalance in Monopodal Stance

Overview

The "static" single-leg stance has been extensively studied in the literature for its relevance in functional evaluation, therapeutic exercise, sports training and research for fall prevention (particularly for the elderly and patients with neurological diseases). However, the motor strategies of the supporting limb have been investigated only at the ankle level. In particular it is not known, at the hip, how the muscular system reacts to medial and lateral imbalances. Colonna has hypothesized, basing on a myofascial chains approach, that the balance is managed by the front and back spiral chains. The aim of the present study is to perform a preliminary experimental analysis to verify Colonna's hypothesis, testing a method for the investigation of motor strategies underlying equilibrium. Five healthy subjects will be examined by means of electromyographic analysis of the gluteus maximus, gluteus medius, adductor longus, tibialis anterior and peroneus longus. Subjects will undergo perturbations of their monopodal balance.

The subjects involved in the research will be analyzed at the LAMBDA laboratory (UDGEE), AUSL-IRCCS (Azienda Unità Sanitaria Locale-Istituto di Ricovero e Cura a Carattere Scientifico) di Reggio Emilia. The analysis will be carried out on the right lower limb of each subject. The electromyographic devices will be applied to the tibialis anterior, peroneus longus, gluteus medius, gluteus maximus and adductor longus. Reflective markers will then be applied (using double-sided tape) according to the Total3DGait protocol, which identifies the body segments of the forearms, arms, trunk, pelvis, thighs, legs, and feet. The subject must position himself with his right foot on a force platform. The toe of the left foot will be allowed to rest on the ground (on the other power platform posteriorly placed), with the verbal indication to load as little weight as possible on it: this indication is aimed at reducing muscle activation in the absence of external perturbations, in order to highlight only the activity caused by the perturbations themselves. Only acquisitions in which the load on the left foot will be less than 30% of the weight will be considered valid. The hands will be placed on the hips to limit the variables to be controlled and to standardize the posture, in order to focus the contribution to the balance of the lower limb. The left thigh has to be kept vertical. Finally, it will be required to find, within the constraints described above, the posture that is as comfortable as possible, with minimal muscle contraction. The distance between the feet is therefore freely chosen by each subject. The operator positions himself behind the subject to be examined, and without being seen performs lateral thrusts with the medial margin of the hand at the proximal third of the thigh. At least ten pushes per side will be performed, with random timing. The thrusts will be quick but without causing pain. The operator will then request maximal contractions from the subject, in order to normalize the electrical activity of each muscle with respect to its maximum. It will be required to perform the dorsiflexion and pronation of the foot against resistance, then the adduction, abduction and extension of the hip.