Isometric Exercise - Factors Influencing Endurance and Fatigue

Abstract

In two healthy male subjects we have made some preliminary observations of the factors influencing endurance and fatigue during successive sustained contractions at two thirds the intensity of a maximal voluntary contraction of the Quadriceps Muscle. In all experiments subjects sat in an adjustable chair (5), measurements being made with a strain gauge attached to the ankle when the knee joint was flexed to 90°. Fig. 1 shows the relationship between the duration of successive contractions and the interval between contractions, both under normal conditions and when the circulation to the leg was occluded using a sphygmomanometer cuff inflated to 250 mm Hg, immediately prior to starting the series. Each subject was allowed at least 24 hours recovery between each experiment. In the absence of circulatory occlusion more than seven holds were possible, the duration of successive holds being significantly related (p =0.016) to the recovery interval. With circulatory occlusion no more than three holds could be sustained, the duration of the second and third holds being unrelated to the recovery interval. As observed by othere (3, 4) the duration of the first hold was not significantly reduced by prior circulatory occlusion suggesting that muscle blood flow was practically arrested at this relative load.

In receipt of a Swedish Welcome Travelling Research Fellowship