MUSCLE ACTIVITY DURING BEAM WALKING IN NOVICE AND EXPERT SUBJECTS

Abstract

INTRODUCTION: Ankle injuries are a common cause of working days lost in the British Armed Forces. In this study we are comparing the activity of muscles acting about the ankle when walking on a normal floor surface with that when walking on narrow beams and lines. This may help elucidate how the ankle responds to unexpected perturbations, which often cause ankle injury. Beam walking is a good model for investigating the control of the ankle, as it is a challenging motor task that involves aspects of both balance and agility. The difficulty and danger of the task can be modified independently, by adjusting the width and height of the beam. Previous work (Llewellyn et al, 1990) has shown that greater cocontraction of the tibialis anterior and triceps surae muscles occurs during beam walking compared with treadmill walking. This co-contraction may allow the neuromuscular system to stabilise the ankle by increasing joint stiffness. In addition, studies of reflex activity during walking (Prochazka et al. 1988, Llewellyn et al 1990) showed that whilst both the static and dynamic sensitivity of muscle spindles is enhanced during balancing tasks, the actual reflex response to perturbations is reduced when compared with normal walking. The CNS is able to increase spindle sensitivity to enhance sensory input, whilst reducing the gain of the stretch reflex, thus limiting any destabilising consequences of an enhanced reflex response.