A Comparison of Maximal Oxygen Intake of Japanese Female Athletes Determined by Direct and Indirect Methods

Abstract

Changes of the surface and needle electromyogram (EMG) of the biceps brachii in fatigue were investigated.
The subjects kept a 10 kg weight applied to the wrist with the elbow flexed about 90°, until they were not able to maintain the elbow in this position. This exhausting contraction was repeated twelve times with a pause of 30 sec between each contraction until eight times. The pause durations from 9 th contraction to 12 th were longer than 30 sec in order to record the EMG.
The surface EMG were recorded during slight contraction in the biceps brachii after the 9 th sustained contraction, and the needle EMG after 10 th, 11 th and 12 th contractions.
In fatigue which followed exhausting contractions, the percentage of polyphasic action potentials recorded with a concentric needle electrode increased, and the duration of all action potentials decreased (Table 1 & 2). These results were discussed comparing with the characteristic EMG of myopathy and with the previous electromyographic studies on muscle fatigue. The power spectra of the bipolar surface EMG showed the frequency lowering in fatigue (Fig. 2 & Table 3).
It was ascertained that the correlation between the percentage of polyphasic action potentials and that of lower frequency components (below 40Hz) was significant (Fig. 3). It was inferred that increased polyphasic action potentials and the frequency lowering in fatigue was due to synchronization between discharges from different motor units.