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The elderly have a lower ability to reabsorb plasma potassium into muscles, which may have detrimental effects during prolonged exercise. The rate of increase and maximum concentration of plasma potassium (K+) for young men, non-athletic older men and a group of elderly master athletes was measured while subjects exercised to exhaustion on stationary bicycles. Although the older men showed faster rates of K+ increase, their peak concentrations did not rise as high as that of the younger subjects, because the elder group exercised for a shorter time.

To test the effect of heavy exercise on age-related changes in endocrine production, endocrine response of younger (20-year-old) athletes was compared to that of older (50-74 year old) athletes who completed a triathlon. For all subjects, all but one of 13 hormones studied increased over basal levels. The highest peak levels for younger subjects were in dihydroepiandrosterone sulfate and thyroid stimulating hormone. Older subjects had larger increases in norepinephrine and sex hormone binding globulin.

The effect of a 9-month vigorous endurance exercise training on the glucose-stimulated insulin response and glucose disposal rate in 60- to 70-yearolds was assessed. Results showed that plasma insulin levels declined after theexercise program. Moreover, insulin action improved at levels usually found in young subjects. Thus, regular exercise can be effective in reducing hyperinsulinemia while improving insulin action.