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PubMed1987

Cardiovascular reflexes during isometric exercise--role of muscle mass and gravitational stress.

Six healthy males performed sustained static contractions of five arm- and leg muscle groups for 2 min at 40% maximum voluntary contraction (MVC) sitting and supine. Delta heart rate, blood pressure, forearm vascular resistance, and cardiac output increased during contraction incrementing increasingly in the following order: dorsi flexion of ankle, plantar flexion, third finger flexion, handgrip, and knee extension. Muscle ischemia during recovery did not change this order. The cardiovascular responses to static contraction did not relate to muscle mass involved in a simple rectilinear manner. The increments in cardiovascular responses were not reduced in the supine position, although the values were at a lower level, probably due to the combination of a decreased sympathetic nervous activity in the supine position and an increased aortic baroreceptor stimulation induced by the increased stroke volume.

Adult↗
PubMedDate not supplied

[Theoretical analysis of the efficacy of G suits during exposure to continuously increasing gravitational overloads].

A mathematical model of human circulation was employed to examine circulation responses to +GZ acceleration the value of which increased linearly at the rate 0.1 G/sec, using subjects having an anti-G suit on and sitting in a relaxed posture. It has been calculated that the anti-G suit can compensate as much as 83% of the increment of hydrostatic pressure in leg vessels and as much as 57% in abdominal vessels. The suit effect on resistance and capacity vessel properties makes an approximately equal contribution to an increase of the acceleration tolerance threshold. However the occlusion effect of the anti-G suit causes a significant increase of afterload.

Acceleration↗