Abstract
I found that transient development in sustained tension occur before voluntarily, rapid muscle relaxation in elbow flexors and likely contribute to accelerate velocity of muscle relaxation. In this study, I attempted to clarify whether the transient development depended on contraction of phasic muscle.
Electromyograms and evoked potentials in gastrocnemius and soleus muscles were recorded respectively during the muscle relaxation of ankle extensors without flexor muscle contraction. The sustained tensions before muscle relaxation were 10, 20, and 30% of the maximum plantar flexion strength. The following results were obtained:
1) Frequency of appearance of the transient tension development was about 42% at 10% of the maximum plantar flexion strength, but decreased with the increase of the sustained tension.
2) On comparing between the velocity of muscle relaxation with and without the transient tension develoment, the former was significantly faster than the latter only at 10% of sustained tension. (p<0.001)
3) At the transient tension development H-reflex in gastrocnemius was potentiated, but inhibited in soleus muscle.
These results suggest that the transient tension development is due to contraction of the gastrocnemius muscle and inhibition of the activity of soleus muscle via a mechanism that excitation of PT cell evoke IPSPs in spinal slow α-motoneurons.
