Methodological Challenges and Limitations of the Research on Overtraining Syndrome

Abstract

Because overtraining syndrome (OTS) is highly complex and multifactorial, without a clear pathophysiology, with multiple possibilities of complex interactions between risk factors and trigger, different dysfunctional pathways, and abnormal reactions, which in turn leads to a wide variety of combinations of clinical and biochemical alterations, research on OTS is challenging, subjective, and highly sensitive to minor variables, while the assessment for its selection, diagnosis, and evaluation is arduous.

Indeed, some of the most remarkable challenges and limitations of researches on OTS are largely due to its characteristics, and include the facts that the natural course of OTS is inherently unpredictable, goes beyond being a simple and natural consequence of training overload, is highly individual in terms of triggers, manifestations and dysfunctions, leading to unique combinations of stressors and alterations, lacks a single universally present biomarker, requires a multiple-step and time-consuming sequence of exclusion and inclusion criteria for its diagnosis, its potential dysfunctions are not overt (which shows not to be abnormal, from the perspective of general population), but relative instead (only noticed when compared to similar healthy athletes), and therefore not easily detected, is multi-factorial and multi-systemic, and requires control for multiple variables. In addition, the differentiation between mild primary hormonal dysfunctions leading to loss of performance and hormonal dysfunctions caused by OTS is hardly possible unless physical and hormonal behaviors are followed longitudinally.

Researches on actual OTS must have specific design characteristics, including recruitment of natural-occurring OTS; diagnosis based on the current diagnostic criteria; delimitation of the population of athletes without mixing different types of sports and basic characteristics; inclusion of a control group of healthy athletes with similar training patterns and performance, and optional inclusion of an additional second control group of sex-, age-, and BMI-matched sedentary subjects; employment of standardized and validated tests; concurrent evaluation of the different systems, including immunologic, classical, and non-classical inflammatory; glucose and lipid metabolism; muscular and fat tissue parameters; basal and stimulated hormonal, hematological, body composition; and metabolism, psychological, and physical parameters within the same participants.

In conclusion, methodological difficulties on the research on OTS may be the underlying reason for the lack of appropriate studies.