Background: The development of research on exercise physiology in the last several years has allowed to better understand mechanisms affecting exercise performance in athletes. Despite this, the causes of exercise intolerance in athletes are not fully elucidated. The exercise performance is a complex process and regardless of the proper functioning of the cardiovascular system may be subject to significant changes under the influence of nervous system and thermoregulatory mechanisms. The purpose of this work is to assess the relationship between psychomotor performance (sprawność psychomotoryczna – SP), core body temperature (Tc) and exercise performance parameters as measured by spiroergometry (cardiopulmonary exercise testing – CPX) and the diagnostic accuracy of neurothermometabolic index (NTMI) as a new marker of exercise performance in athletes. Material and Methods: Forty-four healthy athletes participated in the study. Each of the examined athletes underwent CPX for the assessment of ventilatory parameters (maximal oxygen consumption – VO₂max, minute ventilation – VE, ventilatory equivalent for carbon dioxide at anaerobic threshold – VECO2AT, maximal carbon dioxide output – VCO₂ and anaerobic threshold), SP tests (average reaction time to light stimulus, the number of correctly received light stimuli, number of missed light stimuli) before and immediately after CPX. In addition, Tc was continually measured during CPX. Followingly, NTMI was calculated using Tc during the maximum exercise, oxygen consumption at anaerobic threshold and average reaction time to light stimulus as measured after CPX. Results: A significant relationship was found between Tc during the maximum effort in CPX and SP after CPX. A significant relationship between SP before CPX and VECO₂AT during CPX was also confirmed. Psychomotor performance shortly after CPX was also significantly related to VCO₂. In addition, NTMI was significantly associated with CPX parameters. Conclusions: The study results confirmed the relevant relationship between SP, Tc during the maximum exercise and ventilatory parameters as measured by CPX in athletes. Neurothermometabolic index is a reliable marker of exercise performance in athletes. Med Pr Work Health Saf. 2025;76(3)