The role of muscle mass in the cardiovascular response to static contractions

1. Eleven men performed static contractions with the fingers (digits II and III), forearm (handgrip) and the knee extensors (knee angle 90 degrees ) at 40% maximal voluntary contraction (MVC) for 2 min. In seven of the subjects handgrip and knee extension were combined, both contractions held at 40% MVC. At the end of the contraction, cuffs were inflated to 250 mmHg for 3 min around the extremity which had been contracting. Continuous measurements were performed of force, heart rate and intra-arterial blood pressure (a. brachialis; 20 cm proximally), before and during contraction as well as during the recovery with and without cuffs inflated.2. Heart rate and blood pressure increased momentarily with the onset of a contraction whereafter a gradual further increase took place. This pattern of response was similar for all muscle groups studied. The increases during the contractions were in the order: fingers, forearm, knee extensors and combined forearm-knee extensors, with the difference between each muscle group contraction being significant.3. In the recovery period from a contraction with the cuff(s) inflated, heart rate returned to control level. Blood pressure also dropped, but remained elevated above pre-contraction level until the cuff(s) was released.4. The present data during contraction are at variance with earlier observations showing that the cardiovascular response to a static contraction is proportional to the% MVC regardless of the muscle mass involved in the contraction. Our findings are in line with the traditional concept of central and peripheral nervous inputs playing a role in the cardiovascular adjustments to exercise, with both the central and the peripheral factors being related to the mass of the muscles engaged in the exercise.