About

A 2-week training camp resulted in 30% decrease of blood testosterone levels with a simultaneous increase in CK creatine-kinase activity in the wrestlers. Several weeks' preparatory training was reported to have increased testosterone level by 5% to 14% in canoeists, and runners, and tennis players. Exercise intensifies the synthesis of testosterone and increases its concentration in blood circulation, but the changes depend on the intensity and duration of exercise. Also, cortisol and IGF-1 are both involved in the inflammatory response and exist on opposite sides of the anabolic-catabolic balance at skeletal muscle tissue. Additionally, IGF-1 levels eventually dropped for the athletes, with an increase in creatine kinase a marker used to assess tissue damage, suggesting a combination of extensive training-induced muscle damage and exhaustive depletion of these endocrine systems.
In turn, as the pituitary-gonadal axis works in a negative feedback loop, increasing AR content will likely result in enhanced tissue uptake of testosterone, thus lowering circulating testosterone. High affinity binding of LHRH in the anterior pituitary activates LH secretion by a calcium-dependent mechanism, resulting in LH secretion (Dufau and Catt, 1979; Fry and Kraemer, 1997). Secretion of LH is principally regulated by LH releasing hormone (LHRH) via portal circulation from the hypothalamus. Once bound to the AR, testosterone is irreversibly converted to dihydrotestosterone (DHT) through the enzymatic action of 5-α reductase (Wilborn et al., 2010). In contrast, there are no differences observed between men and women in relation to intramuscular testosterone concentrations and steroidogenic enzymes (Vingren et al., 2008).
In the cytoplasm, the glucocorticoid receptor is found in a complex with chaperone proteins that maintain a conformation with high affinity binding potential (89). However, overtraining appears to impair the inactivation of active cortisol to cortisone in athletes (175), and may impair anabolic processes as high levels of cortisol decrease skeletal IGF-I synthesis by reducing IGF-I transcript levels (176). Inactivation of cortisol into cortisone acts as another mechanism to protect tissues and cells from the deleterious effects of exercise-related cortisol secretion (175). The acute cortisol response to exercise is highest when the overall stress (volume and/or intensity of total work) of the training period is high (145, 173). During exercise, cortisol increases the availability of metabolic substrates, protects from immune cell activity, and maintains vascular integrity (172). Long term resistance exercise training studies examining resting circulating IGF-I concentrations have been demonstrated to be highly variable with reductions, no change, and elevations with no change or reductions in IGFBP-1 and IGFBP-3 (21).
Data from rodent studies examining motor neurons innervating the quadriceps muscles also suggest testosterone has a neuroprotective role in the L2 spinal segment. Subsequent studies have confirmed testosterone propionate administration to crushed motor neurons can accelerate facial nerve crush recovery (measured as mm outgrowth per day) in male golden hamsters, and a similar effect was also observed in female hamsters in the same study (Kujawa et al., 1991). Cranial nerves contain androgen receptor mRNA and protein (Yu and McGinnis, 1986, Drengler et al., 1996) and are another well-studied model of androgenic neuroprotection on rodent motor neurons. In males rats, castration at 60–80 days of age decreases soma size while testosterone treatment of females increases soma size, but not to the extent seen in males (Breedlove and Arnold, 1981). Testosterone establishes the sex difference early by preventing normal cell death as prenatal block of androgen receptors (AR) with the anti-androgen flutamide in males results in the loss of the motor neuron pool (Breedlove and Arnold, 1983a) while perinatal testosterone propionate treatment of females preserves the nucleus (Breedlove and Arnold, 1983b, Nordeen et al., 1985, Sengelaub and Arnold, 1986). These data also raise the question of "Which hormone(s) (or other circulating factors) exert effects on the motor system? Evidence from animal parabiosis studies suggest that linking the circulatory systems of young mice and old mice enhances skeletal muscle regenerative capacity in old mice with no detectable negative effects in young mice (Conboy et al., 2005).
With exercise training, the body adapts to regulate glucocorticoid sensitivity in some cell types (172). In addition, overexpression of GRβ enhances myotube formation and reduces glucocorticoid responsiveness in mouse muscle cells (201). Elevated levels of GRβ in immune cells correlate with reduced sensitivity to glucocorticoids (168). Compared to GRα, GRβ does not undergo ligand-induced down regulation and has an increased half-life (195). In addition, unlike GRα, GRβ is located primarily in the nucleus of cells independent of hormone administration (195). Unlike the GRα, GRβ has a truncated ligand-binding domain that prevents glucocorticoid binding and causes glucocorticoid resistance (195, 201). Glucocorticoid-induced muscle catabolism results from degradation of contractile proteins which begins in the myosin filaments and then spreads to the thin filaments and the z-line (213).