Involvement of Myofascial Spiral Chains of the Lower Limb in Semi-unipodal Balance: A Pilot Study.

Introduction Single-leg stance has been extensively studied for functional evaluation, therapeutic exercise, sports training, and fall prevention. However, the motor strategies of the supporting limb have been investigated only at the ankle level. It is not known, at the hip, how the muscular system reacts to medial and lateral imbalances. We hypothesize, based on a myofascial chain approach, that the balance is managed by the front and back spiral chains. The aim of this work was to perform a preliminary experimental analysis to verify the spiral chain hypothesis, testing a method to investigate the motor strategies underlying equilibrium. Methods Five healthy subjects (i.e. without neurological or orthopedic pathologies affecting the upright position) underwent perturbations of their monopodal balance while a surface electromyographic analysis of gluteus maximus, gluteus medius, adductor longus (ADD), tibialis anterior (TA), and peroneus longus (PL) was executed. The percentage of electrical activation with respect to maximal contraction was calculated for each muscle investigated. The coordination in activation between the hip and ankle muscles was analyzed by the Pearson correlation coefficient. Results Of the studied muscles, TA (43% of maximal contraction) and gluteus medius (28%) had the average highest reaction to lateral imbalance and the highest correlation coefficient (0.89, p-value<0.01); PL (35%) and ADD (16%) were the most relevant in counteracting the medial imbalance (correlation coefficient=0.83, p-value<0.01).  Conclusion The study was performed on a few subjects, and the muscles of the lower limb were only partially investigated. However, the consistency of the results with former experimental studies provided preliminary evidence of the adequacy of the method adopted. The correlation of hip and ankle muscle activations was in line with the spiral chain hypothesis.