The CNS state regulated by the reticular activation system (RAS) placed in the middle of the brain. RAS has a direct reciprocal connection with the thalamus (the main relay unit), cortical areas that provide behavior control and with the hypothalamus (the main homeostatic control unit), and is involved in the regulation of respiration, blood pressure, and cardiovascular responses. RAS regulates activation of the frontal brain areas involved in the cognitive functions (perception, attention, working memory), and at the same time, it modulates muscle tone and coordinates automatic movements, posture, etc. (Audiffren, 2016).
Moreover, an optimal cortical activation level is in turn dependent on the brain’s homeostasis and metabolic balance. Managing this state ensures that the brain has the appropriate energetic resources to allow for better information processing, decision making, and performance of full range of behavioral responses.
Thus, CNS readiness is the multiparametric concept that include, on one hand, a sufficient level of physiological and psychological activation and on the other hand, a well-maintained balance of metabolic homeostasis and stress-regulation systems.
CNS readiness has been shown to be a key factor for sports performance, following a U-shape curve in performance, where activation below or higher than 60% results in decreased performance (Alert and Landers, 2003).
DC Potential (metabolic homeostasis) registered from the head surface is an integrated index that reflects the general non-specific reaction of the organism to stress and represent integration and balance within stress-regulation systems, energy homeostasis, hemodynamic and oxygenation. DC potential reflects the general level of brain activation and CNS readiness in athletes (Iluchina and Zabolotskikh, 1997).
Furthermore, DC potential has also been shown to reflect the level of cortical excitability and is associated with cognitive functions: intention to act, attention, memory, preparatory set, etc. (Kort and Rix, 1979; Lang et al., 1988; Pleydell-Pearce, 1994; Vanhatalo, 2004; Ilyukhina, 2015).
DC potential dynamics and features (amplitude, form, stabilization time, etc.) represent changes in the brain's metabolic balance in response to increased exercise intensity or psychological challenges and are linked to cognitive and mental load (Iluchina, 2015, Wagshul et al., 2011).
Significant alterations in DC potential related to the decreased capacity of metabolic systems to maintain the homeostatic balance in the brain that affect cognitive and emotional control, increases anxiety and results in errors and decreased performance. (Iluchina and Zabolotskikh, 2000; Kara et al., 2020).
Following features of the DC potential were identified as significant for sport performance monitoring (Iluchina, 1986):
The initial level of CNS activation – amplitude of DC in mV (active rest condition).This level reflects the current state of the CNS. Cerebral blood flow (CBF) and the brain metabolism in balance if and initial amplitude of DC potential stays at the range of -45 +5mV.
Operational rest state – DC amplitude after stabilization. Normal level in the range between 25 to 40 mV. “Operational rest” state is the physiological basis for mobilization, readiness and concentration.
DC potential form – DC potential form represents the dynamic interaction within stress- regulation systems. DC potential form can indicate the level of CNS activation balance, emotional stability-instability, exhaustion etc.
DC stabilization speed – measured in minutes. The spontaneous relaxation speed represents neuroreflex reactivity (neural control of baroreflex arch) of cardiovascular and respiratory systems. This measure associated with psycho-emotional dynamic and stability (Iluchina and Zabolotskikh, 1997).
Normal stabilization time occurs around 2 to 3 minutes and represent optimal balance within stress-regulation systems
Moderately slow relaxation (up to 5 minutes) reflect the slight disbalance within stress-regulation systems
Very slow spontaneous relaxation (up to 7-8 minutes) – significant imbalance within stress-regulation systems