[The role of clinical laboratory testing in athlete monitoring: health, performance, and prevention of overtraining].

Physical activity provides numerous health benefits but may also be associated with biological alterations related to training intensity, nutritional deficiencies, overtraining, or doping practices. This article reviews the main biological parameters used in athlete monitoring and their relevance for assessing health status, adaptation to exercise, and performance. These parameters encompass hematological, biochemical, and endocrine markers. The complete blood count enables the evaluation of blood cell adaptations to exercise and the detection of anemia or abnormalities in erythropoiesis. Biochemical investigations provide information on iron and vitamin status, inflammation, muscle integrity, renal function, fluid and electrolyte balance, and energy metabolism. Assessment of hormonal axes, particularly the corticotropic, gonadotropic, and somatotropic axes, contributes to the evaluation of training adaptation and the identification of conditions such as low energy availability and overtraining. Some biomarkers may also assist in the detection of doping practices. Interpretation of laboratory results requires consideration of the physiological adaptations induced by exercise, the sport discipline, training load, and the time elapsed since the last exercise session. Blood sampling should ideally be performed at least 48 hours after intense exercise. In the absence of universal recommendations, biological monitoring should be individualized. The medical laboratory specialist plays a central role in selecting appropriate tests and interpreting results to help preserve athletes' health.