Aging and physical fitness are more important than obesity in determining exercise-induced generation of GH.

Exercise is a potent stimulus for GH secretion. Aging and obesity are associated with a diminution of GH secretion. We wanted to determine whether age or fat mass is more important in regulating the GH response to exercise. Four groups of healthy men were studied: seven lean young men [age, <40 yr; body mass index (BMI), <25 kg/m(2)], six overweight young men (age, <40 yr; BMI, >27.5), seven lean older men (age, >60 yr; BMI, <25), and 6 overweight older men (age, 60 yr; BMI, >27.5). The men performed a maximal exercise test. GH secretion was higher in the younger men than in the older men. Peak GH was higher in the older lean men than in the older overweight men. There was no difference between the young groups. Fitness correlated negatively with age and positively with peak GH. In young men, there was no relation between BMI, bioimpedance, or leptin and GH secretion. In contrast, in older men there was an inverse correlation between measures of fat mass and GH secretion. Age and physical fitness are more important than body fat in regulating exercise-induced GH secretion. These findings have important clinical implications if we are to prevent the frailty and morbidity associated with aging.