Voluntary toe-walking gait initiation:: electromyographical and biomechanical aspects

This study was carried out to investigate the biomechanical constraints of toe-walking gait initiation and the associated changes in motor program compared to the well documented heel-toe walking gait initiation. Seven healthy subjects volunteered for this study. Gait was initiated on a force platform, at three self-selected speed conditions, from an erect spontaneous posture in the control situation (CS) and from a posture with heels raised in the test situation (TS). Surface electromyographical (EMG) activities of muscles soleus (Sol) and tibialis anterior (TA) were recorded on both limbs. We analysed the consequences of the heel-off posture on EMG patterns and biomechanical activities. Whatever the speed condition, the centre of foot pressure was initially located more ahead of the ankle axis in TS than in CS, with an increased Sol and TA EMG activity. The EMG pattern which expresses the motor program governing gait initiation was modified in TS in comparison to CS and induced adaptations of the anticipatory postural adjustments (APA) that precede toe-off of the stepping limb. A lengthening of the APA duration allowed the subjects in TS to reach a gait velocity similar to the one obtained in CS at the end of the anticipatory movements and also at the end of the first step. In TS, the velocity of the centre of gravity at time of toe-off covaried, as in CS, with CG velocity at the end of the first step, still resulting from TA muscular actions during the APA but also probably from other combined muscular actions.