The linear relaxation (LR) was studied in isometric unfused tetanus (UT) of the human flexor digitorum sublimis muscle. With a decrease of the force level, the shoulder on the relaxation curve, as measured from the last stimulus, shifted to the right. The length of the linear portion itself weakly depended on activation level. When steady force changed from 100 to 40-50 % of the maximum, the slope of LR decreased only by 15±4 %. At smaller force levels the slope began to increase. LR can probably also be hidden in the twitch. With increased tetanus duration, LR becomes longer and slower at all force levels. LR was markedly diminished in contraction on the steep part of the exponential relaxation after a smooth tetanus. Its full recovery needed a train of 4-5 pulses (near 1 s) at the new stationary level. The form of the response to the additional pulse given during relaxation remained approximately constant during the most of LR portion and differed markedly before and after it. LR did not have direct relation to fatigue: in the first UT LR was always slower and longer than in subsequent ones.
This study was designed to evaluate the extent of foot deformation in healthy subjects during standing on an immobile support and during slow 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 real changes of the angle in ankle joint during standing on an immobile platform were up to 2 times smaller than the changes of angular position of the shin relative to vertical axis. However, considerable intersubject variability was observed in this respect. During slow tilts of the support platform a marked divergence was observed in the shape of recordings of two "ankle angles" in subjects with high foot compliance. 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 direction. In 12 subjects, the average foot compliance was
0.04 ±0.03 deg/Mm (maximal value 0.1 deg/Mm). It can be assumed that the mechanical properties of the foot can appreciably influence the afferent outflow during maintenance of orthograde posture in man.