Growth hormone release during acute and chronic aerobic and resistance exercise: recent findings

Immuno-endocrine and metabolic responses to long distance ski racing in world-class male and female cross-country skiers

The purpose of this study was to characterize the extent of immune, endocrine, substrate and metabolic changes during a long-distance cross-country ski race in extremely well-trained athletes and evaluate if the blood perturbations would indicate signs of health risk. Ten male (M) and six female (F) national team skiers were investigated as they followed their usual routines of race preparations. Blood samples were drawn before and immediately after a World Cup 50-km M and 30-km F ski race with a mean finish time of 142 and 104 min, respectively. Hemoglobin, electrolytes, and C-reactive protein remained unchanged for both M and F. Serum testosterone remained unchanged in M, but doubled in F. Significant increases were observed in concentrations of granulocytes (F: 5 x, M: 5 x), natural killer cells (F: 2 x, M: 1.5 x), adrenaline (F: 12 x, M:10 x), noradrenaline (F: 7 x, M:5 x), growth hormone (F: 30 x, M: 2 x), cortisol (F: 1.5 x, M:2 x), glucose (F: 2 x, M:1.5 x), creatine kinase (F: 2 x, M:2 x), uric acid (F: 1.5 x, M: 1.5 x) and non-organic phosphate (F:2 x, M:2 x), while insulin concentration decreased (F: 0.5x, M: 0.8 x). Free fatty acid (FFA) concentration increased (F:2 x, M: 3 x). In conclusion, we observed substantial changes in several immuno-endocrine, substrate and metabolic measurements after long distance cross-country ski racing and suggest that some of these marked changes may reflect the large amount of muscle mass involved during skiing.

Reproducibility of the growth hormone response to sprint exercise

OBJECTIVE

There is a large inter-individual variation in the growth hormone (GH) response to exercise, but within-individual variation is unknown. The purpose of this study was to determine the reproducibility of the GH response to a single 30 s sprint on a cycle ergometer.

DESIGN

Eleven non-obese male volunteers completed two trials separated by at least seven days during which they completed a single all-out 30 s sprint on a cycle ergometer followed by 60 min of rest. Blood samples were taken at rest and at regular intervals post-exercise.

RESULTS

No differences were found in mean power output during the sprint, or in peak blood lactate concentrations or lowest measured pH following the sprints. Re-test correlation was significant for both peak GH concentrations (r=0.97, P<0.05) and GH AUC (r=0.97, P<0.05). Within-subject error (change in mean+/-typical error) of the peak GH concentrations and GH area under the curve (AUC) was 4.3+/-3.4 microg l(-1) and 2.9+/-54.3 min microg l(-1), respectively. Within-subject percentage error (percentage change in mean+/-typical percentage error) for peak GH concentration and GH AUC was 33.5+/-26.7% and 1.1+/-20.0%, respectively.

CONCLUSION

Growth hormone AUC is a reproducible measure of the GH response to sprint exercise.

GH responses to a near-maximal exercise training session on-the-field in cyclists

Acute plasma GH response to prolonged (1 h) near-maximal exercise was studied in 7 elite cyclists (6 males, 1 female; mean age +/- SE: 24.9 +/- 1.4 yr) during a routine training session on an uphill track (length: 22.0 km, average slope: 4.39%) and during a recovery (REC) period of 60 min from the end of exercise. The training session entailed a warming-up (WARM) phase of about 20 min at 63% of individual maximal heart rate (HRmax) followed by a high intensity exercise (HIE) phase of about 60 min at 90-92% of HRmax. GH resting values averaged 0.2 +/- 0.06 ng/ml; average GH concentration attained a maximal value (21.5 +/- 3.3 ng/ml, range: 11.0-38.2 ng/ml) between 20 and 40 min of HIE and significantly decreased thereafter (p=0.01), although exercise intensity was unchanged in the following period (p=0.14). After WARM, GH concentrations were significantly lower than peak values (p=0.05). During REC, GH levels steadily decreased, attaining a value of 2.6 +/- 0.8 ng/ml 60 min after the end of exercise. It was concluded that during prolonged and sustained exercise on-the-field in cyclists, GH value determined at the end of the bout may not correspond to the maximal value, which can be observed after 20 to 40 min of near-maximal exercise.