The purpose of this study was to investigate the influence of the size of active muscle mass on the responses of the blood pressure and the heart rate to isometric contraction.

The isometric torques of the flexors and extensors of the knee (90^o), ankle (0^o), elbow (90^o) and wrist (0^o) were measured for 6 seconds in 30 normal, healthy men, between the ages of 20 and 29 years, using the Extremity Training & Rehabilitation System (Model No. Cybex 340).

The peak torque and the time to peak torque were measured for each contraction. In addition, heart rate and blood pressure were recorded simultaneously at rest and immediately following contraction completion at 1 and 3 minutes.

The increase in heart rate and blood pressure during isometric contraction was independent of the size of the contracting muscle mass (p<0.05). The mean increment ratio was 17.3% for systolic blood pressure, 13.2% for diastolic pressure and 39.9% for heart rate.

The mean rime to peak torque for the large muscle groups was longer than the mean time to peak torque for the small muscle groups (p<0.01).

It was concluded that the magnitude of the cardiovascular response to isometric exercise is not influenced by the size of the contracting muscle mass.