A new methodology to re-educate muscle synergies observed during gait

Abstract

Analysis of multiple electromyographic activities suggests that central and peripheral neurological structures modulate the relative amplitude and time course of specific muscle groups during gait. Following neurological insult such as stroke, spatiotemporal characteristics of the four muscular modules or synergies identified during gait (C1, C2, C3 and C4) are impaired. The objective of the present work is to develop a new methodology to recruit synergies involved in gait. The subject is seated with his trunk leaning back and his foot fixed on a multidirectional force transducer, interfaced to a laboratory computer. The centers of rotation of the hip, knee and ankle joints are determined to estimate the lengths of the different segments of the lower limb. In addition, the relative angles between these segments are measured using a goniometer. In order to recruit different muscle synergies during progressive effort, a visual feedback was provided to the subject allowing him to control the direction and magnitude of the static force vector exerted in the sagittal plane of the foot. By measuring the location of the center of pressure exerted and the direction of the force vector applied at the extremity of the lower limb, it is possible to calculate the different moments of force exerted at the hip, knee and ankle using morphometric values of the subject. Seven healthy subjects were asked to exert progressive static efforts in eight sagittal directions while the activities of eight muscles of the lower extremity were recorded using surface electrodes. The muscle synergies elicited in specific directions during these efforts were highly similar to three of the four modules previously identified during gait (C1, C2 and C4). It is suggested that this methodology can provide a basis to establish a training program re-educating muscle synergies of the lower limb that are specifically recruited during gait.