Cardiovascular Response of Human Subjects to Isometric Contraction of Large and Small Muscle Groups

Abstract

Summary

Sustained static (isometric) contraction of striated muscle to fatigue was carried out in normal, untrained, young (22 to 29 years) male subjects in order to compare the hemodynamic response of large (ankle plantar flexor) and small (little finger adductor) muscle contraction. There were pronounced increases in systolic and dia-stolic pressures and heart rates in all cases. The increases in systolic pressure were similar during static contraction of the two different muscle groups; however, diastolic pressure increases were greater and heart rate increases less with finger contraction as compared to leg contraction.

Upon three weekly repetitions, the cardiovascular responses were not significantly altered although the force output was increased with repetition in the case of both muscle groups. The results indicate that (i) although the size of the muscle mass influences the diastolic pressure and heart rate response, the relative muscle tension is the major factor determining the hemodynamic result; (ii) the divergence of blood pressure and heart rate responses suggest a dissociation of the mechanisms governing these two variables in static exercise; and (iii) the relative consistency of the hemodynamic changes during these tests indicates that isometric exercise is a simple and reliable method to study cardiovascular response to stress.