THE CONTRIBUTION OF FOOT DEFORMATION TO THE CHANGES OF MUSCULAR LENGTH AND ANGLE IN THE ANKLE JOINT DURING STANDING IN MAN

This study was designed to evaluate the extent of foot deformation in healthy subjects during standing on an immobile support and during slo w tilts of the support platform by 1 deg. The angle in ankle joint was evaluated by two methods: as an angle of shin inclination relative to the platform and as an angle, calculated on the basis of recording of the projective length of the soleus muscle. It was shown that the rea l changes of the angle in ankle joint during standing on an immobile p latform were up to 2 times smaller than the changes of angular positio n of the shin relative to vertical axis. However, considerable intersu bject variability was observed in this respect. During slow tilts of t he support platform a marked divergence was observed in the shape of r ecordings of two ''ankle angles'' in subjects with high foot complianc e. The vertical displacements of the calcaneus recorded by means of a clamp rigidly fixed at the heel were 0.5+/-0.3 mm (the range 0.1-1 mm) for each degree of body deviation in the forward or backward directio n. In 12 subjects, the average foot compliance was 0.04+/-0.03 deg/Nm (maximal value 0.1 deg/Nm). It can be assumed that the mechanical prop erties of the foot can appreciably influence the afferent outflow duri ng maintenance of orthograde posture in man.