Abstract
In the previous paper the authors reported that a muscular work load resulted in the lowering of the function of concentration maintenance (TAF), the grade of which significantly correlated with the volume of oxygen consumed for the work.
The present experiment has been carried out to discuss about the lowering of TAF due to muscular work from the viewpoint of excitability level of spinal motoneurone, the final common path of motor nerve system, in relation to the physiological function as one of the factors of the change of TAF.
Eighteen healthy male students were loaded with bicycle ergometric work of oxygen consumption of 710ml/min. for 90 minutes. Before and after the work load, they were administered the TAF test, measurement of eye-hand reaction time and recording of H-wave recovery curve from the right lower extremity.
The results obtained were as follows:
1. The function of concentration maintenance tended to lower with muscular work.
2. Comparing the reflexes appeared in H-wave at time intervals of 50 to 900 msec between the conditioning shock and the test shock, the suppression in H-wave recovery curve with ergometric work was noticeable at both 100 and 400 msec against the pre-work values.
3. Lowering of the excitability of spinal motoneurone corresponding to muscular fatigue was revealed by a significant correlation between the inhibition rate in H-wave (post-to-pre value) at 400 msec of shock interval and the time of appearance of irregular Piper's rhythm as myographical fatigue.
It is reasonable that the excitability of spinal motoneurone lowers at 100 msec in the process of after-hyper-polarization, while the fact that even beyond the rage of the process, at 400 msec, a significant suppression in H-wave recovery curve was observed may suggest also a lowering of its excitability without regard to the relative refractory period of after-hyper-polarization.
These results lead us to recognize that the lowering of TAF due to a physical load may be caused by the central depressive action in relation to muscular fatigue.
