A group of long-distance runners and a group whi practice no sport on regular basis, with an age of 20-24 years, carried out a maximum effort test to evaluate the two main stress-activated systems: sympathetic with its endocrine medullar component and the pituitary-adrenal axis, as well as insulin and HGH hormones related to some metabolites used as fuel during the exercise and recovery period.

Prior, informed consent was obtained from each subjects and the project was approved by the Investigation and Ethics Committee of the Faculty of Medicine. A test was designed on a treadmill with a 3 % gradient and 2 km h^-1 progressive increases in speed every 10 min, starting at 6 km h^-1 until exhaustion; for blood samples collection an antecubital vein was catheterized with a system enabling replacement of blood volume extracted with physiological saline solution. Plasma hormone concentrations was determined by RIA, catecholamines by HPLC and metabolites by enzymatic methods.

The results showed maximal plasma concentrations of ACTH, cortisol (C), β-endorphin (β-end) and human growth hormone (HGH) at the end of the exercise test in the trained group (P < 0.01, Student’s t test for paired data). Control subjects exhibited a higher responsiveness compared with trained of catecholamines. Insulin declined during exercise until the end of exercise with the minimal value and maximal for lactate concentrations (P < 0.05). Glucose levels of the control group did not vary during exercise; on the contrary, glucose levels in runners increased at minute 20 of exercise coinciding with HGH and noradrenaline increase. In the control group there were no variations in β-hydroxybutyrate or acetoacetate but in runners there was a significant increase at the end of the exercise and at minute 3 of recovery period of this metabolites (Rudolph et al. 1998).

HGH, ACTH, C and β-end increases are physiological responses to stress in the critical zone next to exhaustion and end of effort test that involve metabolic adaptations during exercise and recovery. The increase in C and β-end delays fatigue and allows a greater workload according to the degree of training of subjects (Diego Acosta et al. 1995). FFA concentrations levels 67 % below baseline values and ketone body changes were statistically significant, indicating the use of this alternative pathway to obtain energy in trained subjects. Linear regression analyses and statistically significant correlation between hormones, metabolites and fitness (r = 0.723: P < 0.05 to r = 0.956: P < 0.001) showed organic adaptations to endurance of trained subjects with homeostatic compromise which necessarily implies an integrated response of the studied parameters.