Stretch Reflex in Rhythmic Hopping Movements

Abstract

During rhythmic hopping in man with both knees extended, electromyograms (EMGs) of the soleus (SOL). medial gastrocnemius (MG), and tibialis anterior (TA) muscles and the ankle joint angle were recorded. In landing phase where triceps surae are stretched, synchronized EMGs were observed in SOL, while MG did not show a clear synchronization. The synchronized EMGs in soleus were apparent at a latency of the segmental spinal stretch reflex. While the subjects were hopping on a plate, which was removed unexpectedly, the synchronized SOL EMGs which have been observed before removing the plate did not appear at the time estimated from the bop immediately preceding. The finding seems to indicate that the synchronized EMGs were not the pre-programmed but the stretch evoked. H-reflex of the soleus was recorded in a standing posture with the same recording condition as applied to the hopping movements. The wave form of H-reflex was almost identical with the synchronized EMGs of soleus. These results indicate that the synchronized EMGs in SOL are the spinal monosynaptic stretch reflex. While SOL and MG showed activities before the contact of the feet with the floor in landing, the activities of MG were more conspicuous than those of SOL EMGs of SOL and MG ended about 100msec after the stretch. It seems, that in rhythmic hopping movements the pre-programmed and the spinal stretch reflex of the triceps surae play an important role.