Effect of high-intensity exercise training on functional sympatholysis in young and older habitually active men

The ability of contracting skeletal muscle to attenuate sympathetic vasoconstriction during exercise, termed functional sympatholysis, can be improved by exercise training. However, to what extent age affects functional sympatholysis is unclear. Thus, this study examined the effect of 8 weeks of high-intensity exercise training on α-adrenergic responsiveness at rest and on functional sympatholysis in a group of young (n = 15; 25 ± 1 years) and older (n = 15; 72 ± 1 years) habitually active, healthy male subjects. Before and after the exercise training, all subjects participated in an experimental day in which leg hemodynamics and venous plasma norepinephrine were assessed at rest and during knee-extensor exercise without and with tyramine infusion. The results of the study show that before exercise training, the young and older subjects had similar α-adrenergic responsiveness at rest and similar incomplete functional sympatholysis during knee-extensor exercise. Exercise training resulted in a reduction in α-adrenergic responsiveness at rest in both groups, whereas functional sympatholysis was improved in the young group only. The improvement in functional sympatholysis in the young but not the older subjects despite a reduced α-adrenergic responsiveness at rest suggests that improving sympatholytic capacity by training may be a slower process in aged than in young men.