Adaptation to stress is determined by an effective interaction of the organism’s neuronal, cardiovascular, homeostatic (pH), humoral and endocrine regulatory systems.
The training process stimulates the development of adaptations in response to physiological or psychological stressors (general adaptation syndrome (GAS)). An intensive training load (stress) drives reorganization of the blood flow, increases muscle mass and muscle stretching, speeds up metabolic processes, stimulates immune and hormonal system and, therefore increases athlete’s sports performance. At the same time, the organism has limited adaptation resources, which are needed to respond to cases of continuous or high level of stress (Selye, 1951). Hence, only optimal training load will bring a continuous improvement over time, whereas frequent as well as insufficient and non- periodic training will end up in stagnation and decline in adaptation (Cunnan et al., 2018).
Optimal training load programming should consider the information that the physiological indices obtained from HRV and CNS measurements carry. Monitoring of the organism’s responses to the training process provides the possibility to validate and redesign the scheduled training routine according to the individual response to the training load.
Systemic stress response triggered by intensive training or by the internal psychological reasons is controlled by CNS. The brain is the most energy-consuming and oxygen-depended organ, and it is highly sensitive to any changes in the cerebral blood flow. Subsequently, inappropriate training load together with psychological events can deplete the brain adaptation resources, increase mental fatigue, and affect performance.