To study the dynamics of alterations in blood hormones and their individual variability during prolonged exercise, changes in plasma levels of corticotropin, cortisol, aldosterone, testosterone, progesterone, somatotropin, insulin and C-peptide were recorded in 32 endurance athletes and 50 untrained persons during a 2-hour exercise on a cycle ergometer at 60% VO2max. Common changes were activation of the pituitary corticotropin function, mostly at the end of exercise, rises in aldosterone and somatotropin concentrations and decreases in insulin and C-peptide levels during exercise. The activation of pituitary-adrenocortical system and the decrease of insulin but not C-peptide levels were more pronounced in athletes than in untrained persons. A large inter-individual variability existed in changes of cortisol, testosterone and progesterone in both groups. Five variants were found in the dynamics of cortisol concentration. Whereas the alterations of corticotropin were characterized mainly by a biphasic increase, the dynamics of corticotropin and cortisol coincided only in one variant out of five. Most characteristic for the postexercise recovery period were decreased activity of the pituitary-adrenocortical system and delayed normalization of aldosterone level.

To evaluate glucocorticoid participation in the control of alanine metabolism during exercise, experiments were performed on adrenalectomized and normal male rats. The adrenal insufficiency prevented the rises induced by 3 h of swimming in alanine levels of blood plasma, red portion of quadriceps, and liver. In normal rats, the rise in alanine content by 65% in blood, 50% in fast-twitch oxidative fibers, and 93% in liver was associated with increased activity of alanine aminotransferase in fast-twitch oxidative-glycolytic fibers (by 23%). In adrenalectomized rats, enzyme activity during exercise did not change in muscles and decreased in hepatic tissue (by 25%). The dependence of exercise-induced changes in alanine aminotransferase activity on glucocorticoids was confirmed by an increased enzyme activity (by 53%) in exercised adrenalectomized rats treated with 125 micrograms corticosterone. In normal rats, training prevented both the rise of blood corticosterone and the activation of hepatic alanine aminotransferase during exercise. The results support the view that the stimulation of the glucose-alanine cycle by glucocorticoids promotes alanine supply and utilization in liver during exercise. In adrenalectomized rats, hepatic arginase activity was decreased during exercise and no elevation of urea levels was found in blood, liver, or skeletal muscles. Consequently, the use of products of the deamination of alanine (and other amino acids) for urea formation also depends on glucocorticoids.

The dependence of exercise-induced hormone responses on sexual maturation was tested in a 3-year longitudinal experiment on 34 girls (aged 11-12 years at the beginning). Sexual maturation was evaluated by Tanners five-stage scale. Children cycled for 20-min at 60% maximal oxygen uptake once a year. Cortisol, insulin, growth hormone, beta-oestradiol, progesterone and testosterone concentrations in venous blood were determined by radioimmunoassay procedures. Basal concentrations of growth hormone increased and of cortisol decreased when breast stage III was reached. Reaching breast stage IV was associated with an increase in basal concentrations of beta-oestradiol, progesterone and testosterone. The exercise induced significant increases in concentrations of cortisol, growth hormone and beta-oestradiol and a decrease in insulin concentration. At breast stage III the increase in cortisol concentration was to a lower level [467 (SEM 42) vs 567 (SEM 46)nmol x l(-1)] and growth hormone concentration to a higher level [29.4 (SEM 0.5) vs 12.8 (SEM 0.4)ng x ml(-1)], while the fall in insulin concentration was less pronounced [postexercise level 10.6 (SEM 0.9) vs 7.8 (SEM 0.8)mU x l(-1)] than in stage II. The magnitude of the cortisol response was reduced in the last stage of breast development (+42.1% vs +55.5% at stage II, +66.2% at stage III, and +50.0% at stage IV). The magnitude of beta-oestradiol response was the lowest in breast stage IV (+15.8%) and the highest at stage V (+41.1%). The progesterone response became significant at stage IV and testosterone response at stage V. In conclusion, we found that reaching breast stage III was associated with altered responses of cortisol, insulin and growth hormone concentrations while the responses of the sex hormone concentrations became pronounced in the last stages of sexual maturation.

The metabolic and hormonal responses to an intensive single-circuit weight-training session were studied in 15 untrained male students. The training programme consisted of ten exercises, employing all the large groups of muscles. Students performed three circuits using a work-to-rest ratio of 30 s:30 s at 70% of one-repetition maximum. The whole programme lasted 30 min. Blood samples were obtained from the anticubital vein 30 min before exercise, immediately after exercise finished and after 1-h, 6-h, and 24-h periods of recovery. The training session produced significant increases in the plasma adrenocorticotropic hormone, cortisol, aldosterone, testosterone, progesterone and somatotropin concentrations. The plasma level of insulin and C-peptide remained unchanged. The strength exercises caused elevated ratios of cortisol:testosterone and cortisol:insulin, indicating a prevalence of stimulation of catabolic processes as well as of mobilization of energy reserves but during the recovery period the reverse of this was observed. Immediately after exercise the mean lactate concentration was 7.19 mmol.l-1, SD 0.56, the glucose concentration increased significantly during exercise and decreased rapidly during recovery. The high density lipoprotein-cholesterol increased in 1-h period of recovery compared with the initial level. The concentration of total cholesterol, low density lipoprotein-cholesterol and triglyceride, did not change. Packed cell volume did not change during exercise or recovery.

Health is determined not only by the absence of disease, but also by an individual's resistance to pathogenic factors. In turn, resistance depends on the effectiveness of specific homeostatic regulation and the mechanism of general adaptation. Through the change in adaptivity, health may be increased or reduced. While it is difficult to predict which specific homeostatic mechanism will be necessary in various stages of life in the individual, it is more reliable to try to improve health, thereby increasing the effectiveness of the mechanism of general adaptation. Physical training results in a variety of changes in individuals. There are several changes which are essential both for increased exercise performance and for increasing adaptivity, by favouring the effectiveness of the mechanism of general adaptation. These changes: improve central nervous regulation and central nervous system functions; increase endocrine system capacity; increase energy potential; improve the capacity of the oxygen transport system; improve oxidation processes; increase metabolic and functional economy; increase functional stability; and increase the number of Na+,K+ -pumps. The influence of these changes on adaptivity is accomplished by the influence of exercise training on immunoactivities, and by the antisclerotic effect of training. The latter may be considered to be metabolic (actualised through the training effect on lipoprotein metabolism and aging-related calcium distribution) or mechanical (protection of tissues from sclerotic changes by their activities) effects. The training effects are specifically dependent upon performed exercises. Endurance exercise is considered to be the most important and widely recommended form of exercise for health improvement. Most of the training benefits (listed above) for increased adaptivity are induced by aerobic endurance training. Gymnastic exercises are indispensable in regard to mechanical antisclerotic effect. They are also essential influences on the central nervous system. Aerobic dance or aerobic rhythmic gymnastics are ways by which the positive effects of endurance and gymnastic exercise can be combined.