Blood Hormones as Markers of Training Stress and Overtraining
Axel Urhausen MD, PhD, Holger Gabriel & Wilfried Kindermann
Sports Medicine volume 20, pages251–276 (1995)
An imbalance between the overall strain experienced during exercise training and one’s tolerance of such effort may induce overreaching or overtraining syndrome.
Overtraining syndrome is characterized by diminished i) physical performance, ii) accelerated fatiguability, and iii) subjective symptoms of stress.
Blood levels of substrates such as lactate, ammonia, and urea - and the enzyme creatine kinase – are some possibilities to be monitored.
Endogenous hormones are needed for physiological reactions and adaptations during physical work and influence recovery after exercise by moderating anabolic and catabolic processes.
Testosterone and cortisol play a significant role in the metabolism of protein and carbohydrate. They are competitive agonists at the muscle cell receptor level. The testosterone/cortisol ratio is used to monitor the anabolic/catabolic balance. This ratio decreases in relation to i) the intensity and duration of single physical exercise sessions and ii) periods of multiple intense training or competition sessions and both can be reversed by regenerative measures.
Correlations have been noted with the training-induced changes of strength, but it is more likely the testosterone/cortisol ratio results from physiological strain in training as opposed to an overtraining syndrome.
The sympatho-adrenergic system might be involved in the pathogenesis of overtraining.
Overtraining appears to disturb autonomic nervous system regulation:
Parasympathetic (unconscious/“rest & digest”) shows:
1) Diminished maximal secretion of catecholamines.
2) Impaired full deployment of anaerobic lactic reserves.
= Decreased maximal blood lactate levels and maximal performance.
Epinephrine (free plasma adrenaline) and Norepinephrine (noradrenaline) may provide additional information for the monitoring of endurance training.
Prolonged aerobic exercise conducted at intensities below the anaerobic threshold lead to a moderate rise of sympathetic activity but workloads exceeding that threshold lead to a disproportionate increase in the levels of catecholamines.
Also, psychological stress during competitive events is characterized by a higher catecholamines-to-lactate ratio compared to physiological stress from training sessions, so the frequency of training sessions with higher anaerobic lactic demands should be carefully limited in order to prevent overtraining.
In the state of overtraining and overreaching, respectively, a decreased rise of i) pituitary hormones (corticotrophin, growth hormone), ii) cortisol, and ii) insulin has been found after an exhaustive exercise test completed at 10% intensity above one’s anaerobic threshold. That altered stress-response corresponds to findings with insulin-induced hypoglycemia from overtraining which suggests an impaired hypothalamic regulation.
However, the role of hormones in the recovery phase and their effect on the receptor and intracellular level need further study. Reference values for “normal” exercise tolerance and easier, less expensive lab methods are still lacking.
External factors that influence hormonal blood levels require well-standardized sampling conditions but are difficult to assess in the training environment. The impaired exercise-induced increases of selected hormones and the consideration of psychological stress from hormonal measurements also require future investigations.