Effect of phasic muscle contraction for acceleration of voluntary muscle relaxation / 体力科学

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.<BR>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:<BR>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.<BR>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)<BR>3) At the transient tension development H-reflex in gastrocnemius was potentiated, but inhibited in soleus muscle.<BR>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.

Transient development of tension at voluntary muscle relaxation in human arm muscles / 体力科学

I have reported that tension development of sustained tension transiently occur at volutnary muscle relaxation. I attempted to clarify relation of the transient tension development and velocity of muscle relaxation in brachial biceps muscle. Obtained results were as follows:<BR>1) The tension followed with muscle relaxation was diphasic. Frequency of the diphasic tension increased depending on the sustained tension level before relaxation.<BR>2) Amount and duration of the transient tension development were below 3% of the tensions and 80 ms, respectively.<BR>3) There was significant relation between amount of the tension develovment and velocity of the muscle relaxation at the sustained tension of 15 (p<0.05) and 20%MVC (p<0.01) .<BR>4) Girth of upper arm detected by using the rubber-strain-gauge method increased at the transient tension development.<BR>From these results, it is suggested that the tension development is related to transient elevation of the central nervous activity and the muscle shortening during the transient tension development accelerated muscle relaxation by decrease of the spindle discharges in muscle.