ABSENCE OF AN EFFECT OF FATIGUE ON MUSCLE EFFICIENCY DURING HIGH-INTENSITY EXERCISE IN RAT SKELETAL-MUSCLE

The effect of fatigue was studied on rat skeletal muscle efficiency du ring maximal dynamic exercise of 10s duration. After the initial 4s of exercise, power output decreased rapidly to 46.2 +/- 6.7% (mean +/- S D; n=6) after 6s of stimulation and further to 17.5 +/- 5.8% in the la st contraction, Both the rates of total work output and high-energy ph osphate consumption decreased with increasing exercise duration, As a result muscle efficiency was not affected by exercise time in the pres ent experiments. This result indicates that fatigue in severe maximal exercise is induced by a feed-back mechanism, which in the case of hig h ATP utilisation rates will reduce ATP splitting probably by reducing Ca2+-release from the sarcoplasmic reticulum.