Effect of arm position on cardiovascular responses during isometric handgrips.

Sixteen subjects (eight women and eight men, age 20-25 years) carried out in the seated position, isometric contractions sustained until exhaustion of the digital flexors. The subject's arm was placed in two positions, high and low. The muscle tensions used were 30, 40 and 50% of maximum voluntary contraction (MVC). Under these conditions, for a given relative force, the duration of contraction (limit-time) was not modified by the arm position. In the male subjects, increases in heart rate (HR) and systolic blood pressure (SBP) were slightly more pronounced in the low than the high position, but the differences were not significant. Limit times in the high position were similar to those in the low position, and, in the absence of an increase in HR and SBP, this seemed to be due to an increase in cardiac output consequent upon a transient improvement in venous return together with an increase in the coefficient of oxygen utilization.