Free Thyroid Hormone Responses to Repeated Wingate Exercise Versus a Non-Exercising Comparison Group in Male Amateur Soccer Players

High-intensity anaerobic exercise induces acute physiological and endocrine responses that contribute to metabolic regulation and athletic performance. Thyroid hormones, including free triiodothyronine (fT3) and free thyroxine (fT4), play essential roles in energy metabolism, oxygen consumption, and exercise adaptation. However, the immediate effects of repeated supramaximal exercise on thyroid hormone responses remain insufficiently understood, and most previous reports lack any non-exercising comparison condition, so observed changes cannot be separated from time of day, posture, repeated venipuncture, or routine analytical variation.

This two-group non-randomized study was designed to compare the acute effects of repeated Wingate exercise on free thyroid hormone concentrations against a non-exercising comparison group. Twenty healthy male amateur soccer players completed a standardized repeated Wingate exercise protocol under controlled laboratory conditions, consisting of six 30-second maximal bouts at 7.5% of body mass separated by 4 minutes of passive recovery. A comparison group of twenty male amateur soccer players provided two venous blood samples on one morning without performing any exercise between them. Venous blood samples were collected immediately before and immediately after the exercise session or the resting interval to determine free triiodothyronine (fT3), free thyroxine (fT4), and thyroid-stimulating hormone (TSH) concentrations. Hormone analyses were performed using standardized laboratory procedures.

The two groups were recruited and sampled in different periods rather than concurrently, and participants were therefore not randomly allocated. The primary objective was to determine whether the change in circulating free thyroid hormone concentrations around a repeated Wingate session differs from the change observed across a comparable resting interval.