Novel Insights in Overtraining Syndrome: Summary and Conclusions

Abstract

The classical understanding of overtraining syndrome (OTS) as being a dysfunction triggered by excessive training or a relative lack of resting that leads to unexplained underperformance and corresponding theories on chronic glutamine and glycogen depletion, central fatigue, autonomic nervous system aberrancies, excessive unrepaired oxidative stress, unbalanced cytokines, and dysfunctional hypothalamic state could partially explain OTS pathophysiology, whereas important gaps in the comprehension of OTS still existed.

The multiple new findings in OTS generated novel scientifically based concepts that helped better understand the OTS pathophysiology, triggers, and other characteristics. OTS can be understood as a result from the sum and interactions between multiple excessive efforts and deprivations, including relative caloric and protein malnutrition, unrefreshing sleep, lack of compensatory reduction of training sessions, and concurrent intense physical and cognitive demands, which lead to chronic glycogen deprivation, excessive unrepaired damage, impaired immune function, dysfunctional increase of cytokines, and chronic mild neuroglycopenic state. The hostile tissue environment resulted from these abnormalities force the development of multiple dysfunctional adaptations to in order to keep surviving and functioning at the same time (maladaptations), which result in exacerbated catecholamines, fat storage accumulation, exacerbated proteolysis, loss of the fight-or-flight response, global blunted metabolic and hormonal responses, and impaired muscle metabolism, toward energy-saving, anti-anabolic, pro-catabolic, and hypometabolism states, multiple losses of the recently unveiled hormonal conditioning processes that occur in athletes, and relative dehydration. The sequence of events eventually leads to OTS, which includes manifestations of mental and physical exhaustion, pathological muscle soreness, loss of multiple abilities in physical performance, increased predisposition to overall infections, and burnout-like signs and symptoms.

OTS was revealed to be neither an overt nor an absent dysfunction, but a relative alteration instead, which supports the hypothesis that OTS is a sort of mix of losses of multiple adaptive conditioning processes that athletes undergo, as a sort of combination of deconditioning processes, and therefore yield different results than those expected for that specific population of athletes. OTS is now understood as a burnout-related, deprivation-derived, and low energy availability (LEA)-triggered dysfunction and is no longer perceived as being exclusively triggered by absolute or relative excessive training but a combination of insufficient protein, carbohydrate or caloric intake, poor sleep quality, concurrent other energy demands, particularly the cognitive ones, and lack of recovery.

Despite the historical and spread use, the term “overtraining syndrome” revealed to be imprecise, since excessive training only covers one of the factors that may lead to OTS, whereas the term “Paradoxical Deconditioning Syndrome (PDS)” synthetizes the key phenomenon and the hallmark characteristic of OTS within a short expression.