Physiological modifications of local haemodynamic conditions during bilateral isometric contractions.

Nine subjects (five women and four men) simultaneously performed two isometric contractions sustained until exhaustion at different relative forces: 40% of maximum voluntary contraction (MVC) for the right elbow flexors; 50% MVC for the left elbow flexors. Contraction of the left elbow flexors commenced at 50% of the limit time (maximum maintenance time) of isometric contraction of the right elbow flexors. Increase in heart rate during concomitant contraction of the left elbow flexors led to an increase in blood flow to the right elbow flexors. Under these conditions, the limit time of isometric contraction of the right elbow flexors was prolonged with respect to the limit time obtained for an isolated isometric contraction at the same relative tension. The difference was more significant in the female (+40%, P less than 0.05) than in the male subjects (+20%, P greater than 0.05).