Age-dependent effect of resistance exercise on growth hormone secretion in people
G Pyka, RA Wiswell and R Marcus
Aging Study Unit, Department of Veterans Affairs Medical Center, Palo Alto, California 94304.
We measured serum GH responses to a standardized circuit of resistance
exercise in 12 young subjects (6 men and 6 women; 27 +/- 1.6 yr old) and in
11 elders (6 men and 5 women; 72 +/- 0.8 yr old). Initial assessment of
strength [1 repetition maximum (1RM)] was made of 12 muscle groups using
Nautilus equipment. One week later, subjects carried out the exercise
protocol, 3 sets of 8 repetitions for each of the 12 exercises, at 70% of
predetermined 1RM values. Venous blood was drawn at baseline, after each
exercise, and every 2 min during 10 min of recovery. In young subjects
serum immunoreactive GH rose by completion of the second exercise,
increased and remained elevated through the remainder of the exercise
period, and decreased toward baseline by 10 min of recovery. In the elderly
subjects, baseline GH values were similar to those in the young (1.76 +/-
0.41 vs. 2.61 +/- 0.73 micrograms/L) and did not increase above 6
micrograms/L at any time during or after exercise. Exercise increased GH in
both groups, but peak values (14.9 +/- 3.5 micrograms/L in young; 2.44 +/-
0.6 micrograms/L in old) and integrated (198 +/- 47 in young; 37.8 +/- 0.8
in old) were significantly greater in the young subjects (P less than
0.05). GH responses showed no gender difference in either group. Brief
increases in pulse rate were observed during individual exercises, but
sustained elevations did not occur. To assess the effect of exercise
intensity on GH response, we compared responses to exercise at 70% and 85%
of 1RM in 7 young and 11 older people. In the young subjects, GH responses
were nonsignificant at 60% and increased progressively at 70% and 85% of
1RM. No significant effect of exercise intensity was observed in the older
subjects. We conclude that resistance exercise promptly elevates
circulating GH concentrations in healthy young adults. This response is
related to the intensity of the resistance stimulus, although a small
contribution of aerobic stress cannot be excluded. The GH response to
resistance activity is grossly diminished in healthy elderly men and women.
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