## 1 Introduction  
Acute physical fatigue profoundly impacts multiple facets of human physiology and psychology, particularly in the domains of muscular function, cortical function, and pain perception. This significance stems from the observation that fatigue not only affects individual health and well-being but also has critical implications for athletic performance, influencing both short-term outcomes and long-term adaptations. This comprehensive exploration integrates various strands of research to offer a cohesive understanding of these interrelated phenomena, thereby underscoring the importance of addressing fatigue in sports science and clinical practice [1; 2; 3]. Musular function is significantly affected by acute physical fatigue, which manifests as a decline in the muscle's ability to generate force. This decline is influenced by a multitude of factors, including metabolic changes, the depletion of energy reserves, and altered recruitment of muscle fibers [4]. During high-intensity activities, muscle fibers experience significant changes such as decreased phosphoreatine stores, lactate accumulation, and ion balance disruption, contributing to fatigue [5]. Additionally, the generation of reactive oxygen species during intense physical activities leads to oxidative stress, further impacting muscle function [6]. Central fatigue also plays a crucial role, involving neural factors like motor neuron excitability and voluntary activation [7]. Furthermore, recent advancements in understanding muscular function under fatigue reveal the concept of'muscle wisdom', where there is a reduction in motor unit firing rates during prolonged activities to preserve muscle force output [8]. Furthermore, near-infrared spectroscopy has provided deeper insights into muscle oxygenation and energy metabolism during fatigue [9], underscoring the complex physiological and biochemical interplay in muscles under exhaustive conditions. The impact of fatigue on cortical function, including processes like motor control, decision-making, and cognitive functions, is profound. Fatigue can alter cortical excitability and the efficiency of neural pathways involved in these processes [10]. It can lead to decreased attention, reaction time, and decision-making abilities, critical in sports performance [11]. Furthermore, recent neuroscientific developments have shown that physical fatigue significantly alters brain activity, particularly in the prefrontal cortex, implicating a direct link between fatigue and cognitive impairment [12]. Transcranial magnetic stimulation studies have demonstrated changes in motor-evoked potentials with fatigue, suggesting alterations in synaptic efficacy and neuronal excitability in the motor cortex [13]. Fatigue impairs the brain's ability to filter out irrelevant stimuli, leading to decreased attentional focus [14], and biases individuals towards more impulsive decision-making [15]. The interaction between mental and physical fatigue highlights the need to consider both aspects in sports and athletic performance [16]. Pain perception, a complex interplay between sensory input and psychological factors, is also influenced by physical fatigue. It is modulated by physiological impacts of exercise and psychological factors like attention, emotion, and motivation [17]. Athletes often exhibit higher pain thresholds, possibly due to physiological adaptations and psychological conditioning [18]. Indeed, studies have highlighted the phenomenon of exercise-induced hypoalgesia, where acute exercise leads to a temporary reduction in pain sensitivity, particularly evident in endurance athletes [19]. This is attributed to physiological factors, like the release of endorphins and endocannabinoids, and psychological factors such as increased pain tolerance due to regular exposure to physical stress [20]. Mental fatigue exacerbates pain perception and impairs performance, indicating a complex link between cognitive fatigue, pain processing, and physical performance [13].