Blunted Growth Hormone Response to Maximal Exercise in Middle-Aged Versus Young Subjects and No Effect of Endurance Training

• Published in: The journal of clinical endocrinology and metabolism Vol. 84; no. 7; pp. 2303 - 2307
• Main Authors: Zaccaria, Marco, Varnier, Maurizio, Piazza, Paolo, Noventa, Donatella, Ermolao, Andrea
• Format: Journal Article
• Language: English
• Published: Endocrine Society 01-07-1999
• ISSN: 0021-972X; 1945-7197
• DOI: 10.1210/jcem.84.7.5853

The purpose of this study was to evaluate the GH response to exercise
and the effects of endurance training on this response in early
middle-aged men. Seven healthy middle-aged [M; 42.0 ± 2.4
(±sd) yr old] and five young (Y; 21.2 ± 1.1 yr old)
competition cyclists were investigated before and after 4 months of
intensive endurance training. Subjects performed an exhaustive
incremental exercise test (50 watts for 3 min) with gas exchange
measurement, and blood samples for lactate, glucose, and GH
determinations were drawn before exercise, at the end of the exercise,
and in the recovery phase (1, 3, 5, 10, 15, 20, and 30 min). Basal
insulin-like growth factor I was also determined. At exhaustion no
differences were found in relative maximal heart rate or blood lactate
and glucose peaks. On the contrary, the two groups had markedly
different GH responses; in fact, the peak GH response to exhaustive
exercise was much lower in M than in Y (8.1 ± 1.3
vs. 57.1 ± 15.5 μg/L; P <
0.01). The training, similar in subjects of the same group, increased
progressively from 182 to 300 km/week (+64.8%) in M and from 350 to
600 km/week (+71.4%) in Y.
After the training, the percent increase in maximal oxygen consumption
was similar in the two groups (M, +15.2%; Y, +17.5%), confirming that
the efficiency of the training performed was comparable. In neither
group did training have any effect on the GH peak response to exercise,
confirming the blunted GH response in M compared to Y (6.7 ± 1.0
vs. 61.0 ± 12.9 μg/L; P <
0.01). Similarly, insulin-like growth factor I concentrations were not
significantly affected by training.
In conclusion, active middle-aged subjects, compared with the young,
showed a blunted GH response to a physiological stimulus such as
exercise, indicating that the age-related decline in GH secretion
appears in early middle age. This response was not modified by training
in either early middle-aged or young subjects.