Relationship of physical exercise and ageing to growth hormone production

The normal decline in physiological function with ageing is associated with a decrease in bioavailable growth hormone. Growth hormone has been shown to alter body composition and increase fat-free mass in older men. Increased physical fitness is accompanied by an increase in 24-h growth hormone release. The purpose of this study was to examine the effect of exercise on declining growth hormone concentrations with increasing age.

The growth hormone production of 10 male subjects running over 40 miles per week was compared to 10 healthy age-matched sedentary males (controls 57.7 +/- 2.8 vs. runners 60.5 +/- 3.4 years). All subjects underwent a basal assessment including a two-hour serum growth hormone profile followed by estimation of maximal exercise capacity on a cycle ergometer with growth hormone estimations at peak exercise activity and every five minutes whilst cycling at 40% of maximal exercise capacity.

Maximal exercise capacity confirmed the lifestyles of the two groups (VO2 max controls 22.36 +/-6.05 vs. runners 34.91 +/- 13.13 l/min/kg, P = 0.01). The runners had lower body-mass indices than controls (BMI 22. 3 +/- 1.5 vs. 25.5 +/- 2.0 kg/m2, P = 0.002). Peak growth hormone level during a two-hour resting profile was higher in the runners (median (range) controls 2.10 (0.20-12.20) vs. runners 5.25 (0.80-21. 00) mU/l, P = 0.03) as was the average growth hormone level during the two hour profile (mean growth hormone per 2 h median (range): controls 0.54 (0.03-4.88) vs. runners 2.17 (0.25-7.45) mU/l, P = 0. 04). Growth hormone production at maximal exercise capacity was similar. Sex hormone binding globulin and testosterone were significantly higher in the runners.

The results suggest that regular intensive exercise in older male subjects is associated with higher growth hormone and testosterone levels and that exercise may have a role in counteracting the normal decline in growth hormone with ageing.