Heart rate modulations in overtraining syndrome

Abstract

Every sports training program comprises a component of repetitive overloading, but in the case of lack of recovery it may produce undesired effects such as the absence of performance improvement and chronic fatigue. The state of underperformance, known as the overtraining syndrome (OTS), is in a relation with a number of physiological and psychological symptoms of maladaptation, and it may take weeks, months and sometimes years to restore proper sports form. Although investigated for decades, the mechanism of overtraining, and more importantly the tools for early detection of overtraining, are still not defined. Besides other physiological, biochemical, immunological, psychological and performance markers, heart rate (HR) and its modulations are intensively investigated as a practical and reliable sign of overtraining. In general, resting bradycardia, a decrease in HR during submaximal exercise, an increase in speed of heart rate recovery and increased vagal-related heart rate variability indices are all well accepted markers of improved aerobic fitness. In contrast, opposite changes in these HR measures are commonly interpreted as indicators of detraining, chronic fatigue, non-functional overreaching or overtraining. However, based on the limited and diverse literature available, those parameters may be proposed for monitoring training status, optimizing training programs and following accumulation of fatigue, but their role in overtraining detection and assessment is still to be elucidated. There is a strong need for well controlled prospective studies where a longitudinal follow-up of athletes is performed, but since it is certainly unethical to excessively train an athlete in such a way that he develops OTS, a well animal experimental model of OTS may help understanding the „unexplained underperformance syndrome”.