## 4 Discussion  
The research aimed to assess the physiological, biomechanical, and thermographic responses of male athletes during an ultra-endurance race. Findings revealed alterations in heart-rate variability metrics, suggesting increased cardiovascular demands and heightened sympathetic activity. While neuromuscular and perceptual metrics like flicker fusion, handgrip, and horizontal jump remained stable, there was a significant weight reduction, indicating potential dehydration and energy expenditure. Urinalysis highlighted consistent pH, colorimetry, and glucose levels but a notable increase in proteinuria after the third stage, hinting at renal stress. Thermographic data showed increased body temperatures in the face, chest, abdomen, and arms but decreased temperatures in the legs. Ultra-endurance events provide a unique scenario for directly assessing the adaptability of the human body [2]. These extreme physical challenges not only test the limits of human performance but also offer valuable insights into how the body responds and adapts to prolonged, intense stress [1]. This aspect makes ultra-endurance events an invaluable tool for understanding the physiological, biomechanical, and psychological dimensions of human endurance and resilience [4,10]. In the study, heart-rate variability (HRV) analysis during the four stages of the ultra-endurance event revealed a decline in parasympathetic activity and a rise in sympathetic nervous system activation, aligning with similar findings in ultra-endurance running events [8,25]. Notably, autonomic modulation remained unchanged across the stages. This is a unique observation in multi-stage ultra-endurance walking events, as previous research primarily focused on cycling events, where HRV showed significant declines, indicating altered autonomic nervous system function [26]. The methodology of HRV assessment, varying stage lengths, and the distinction between walking and cycling activities could account for these differences. The study's results suggest that each stage imposed a consistent level of stress on the autonomic nervous system, regardless of accumulated fatigue. This could be attributed to the event's low intensity, which might have allowed sufficient recovery for the athletes to maintain a consistent performance level across stages [8,25]. In our multi-stage research, we understand that anticipatory anxiety before the competitive race, which affects parasympathetic activity, would have an exclusive effect on the pre-event measurement, similar to that reported in the literature [27]. Possibly, in our study, as it involves a noncompetitive multi-stage event, the rest of the pre-stage measurements were influenced by an adaptation process. Specifically, the literature shows that after completing a 64 km ultramarathon event, parasympathetic-related indices require 2 days to return to initial values. However, subjective measures of fatigue and well-being indicate that athletes need 5 days after the event for full recovery [28]. Regarding cortical arousal, a decline was observed at the end of each stage, indicating that while the event induced stress and potential central nervous system fatigue [29,30], it might not have led to significant mental fatigue, which could positively favor the recovery process between stages [31, 32, 33]. The metabolic response of participants in the ultra-endurance event was marked by elevated blood lactate concentrations at the conclusion of each stage, suggesting a