BLOOD HORMONES AS MARKERS OF TRAINING STRESS AND OVERTRAINING

An imbalance between the overall strain experienced during exercise tr aining and the athlete's tolerance of such effort may induce overreach ing or overtraining syndrome. Overtraining syndrome is characterised b y diminished sport-specific physical performance, accelerated fatiguab ility and subjective symptoms of stress. Overtraining is feared by ath letes yet there is a lack of objective parameters suitable for its dia gnosis and prevention. In addition to the determination of substrates (e.g. lactate, ammonia and urea) and enzymes (e.g, creatine kinase), t he possibilities for monitoring of training by measuring hormonal leve ls in blood are currently being investigated. Endogenous hormones are essential for physiological reactions and adaptations during physical work and influence the recovery phase after exercise by modulating ana bolic and catabolic processes. Testosterone and cortisol are playing a significant role in metabolism of protein as well as carbohydrate met abolism. Both are competitive agonists at the receptor level of muscul ar cells. The testosterone/cortisol ratio is used as an indication of the anabolic/catabolic balance. This ratio decreases in relation to th e intensity and duration of physical exercise, as well as during perio ds of intense training or repetitive competition, and can be reversed by regenerative measures. Correlations have been noted with the traini ng-induced changes of strength. However, it seems more likely that the testosterone/cortisol ratio indicates the actual physiological strain in training, rather than overtraining syndrome. The sympatho-adrenerg ic system might be involved in the pathogenesis of overtraining. Overt raining appears as a disturbed autonomic regulation, which in its para sympathicotonic form shows a diminished maximal secretion of catechola mines, combined with an impaired full mobilisation of anaerobic lactic reserves. This is supposed to lead to decreased maximal blood lactate levels and maximal performance. Free plasma adrenaline (epinephrine) and noradrenaline (norepinephrine) may provide additional information for the monitoring of endurance training. While prolonged aerobic exer cise conducted at intensities below the individual anaerobic threshold lead to a moderate rise of sympathetic activity, workloads exceeding this threshold are characterised by a disproportionate increase in the levels of catecholamines. In addition, psychological stress during co mpetitive events is characterised by a higher catecholamines to lactat e ratio in comparison with training exercise sessions, Thus, the frequ ency of training sessions with higher anaerobic lactic demands or of c ompetition, should be carefully limited in order to prevent overtraini ng syndrome. In the state of overtraining syndrome and overreaching, r espectively, an intraindividually decreased maximum rise of pituitary hormones (corticotrophin, growth hormone), cortisol and insulin has be en found after a standardised exhaustive exercise test performed with an intensity of 10% above the individual anaerobic threshold. This dis turbed stress-response corresponds to findings with insulin-induced hy poglycaemia in overtraining suggesting an impaired hypothalamic regula tion. However, the role of hormones in the recovery phase and their ef fect on the receptor and intracellular level remain to be better estab lished. Reference values indicating a 'normal' exercise tolerance as w ell as easier and less expensive laboratory methods are still lacking. External factors influencing the hormonal blood levels require well-s tandardised sampling conditions which are often difficult to realise i n the training environment. The impaired exercise-induced maximal incr ease of selected hormones and the potential consideration of the psych ological stress component by hormonal measurements, however, represent interesting basic findings which encourage future investigations.