Metabolic, Endocrine, and Neurotrophic Responses to a 4v4 Small-Sided Game Following Brief Music or Mindfulness After a Mental-Fatigue Exposure: A Randomized Crossover Trial

Background/Objectives: Prolonged cognitive load, including short-form social-media use, may influence soccer-specific performance, yet the perceptual, metabolic, endocrine and neurotrophic effects of brief post-fatigue strategies such as music and mindfulness remain unclear. This study compared 15 min music, 15 min mindfulness (body scan) and time-matched control after a 45 min short-form social-media mental-fatigue exposure. Methods: Sixteen trained male soccer players completed a randomized, counterbalanced, repeated-measures crossover trial. Each session comprised the exposure, condition, a standardized warm-up and a 4v4 small-sided game (SSG). Venous blood was obtained pre-protocol (T1) and approximately 5 min post-SSG (T2) for serum lactate, cortisol and brain-derived neurotrophic factor (BDNF). Perceptual and technical-performance outcomes were also analysed using linear mixed-effects models. Results: Post-condition mental-effort scores differed by condition (F(2,30) = 12.117, p < 0.001) and were lower in music and mindfulness than in control in a time-point-specific model, although baseline mental effort also differed between conditions; perceived mental fatigue, post-SSG exertion and enjoyment did not differ. Condition effects emerged for successful passes (p = 0.020), ball recoveries (p = 0.010) and ball losses (p = 0.018), all highest during mindfulness; pass success percentage, shot outcomes and net ball recovery were unchanged. Overall lactate (p = 0.013) and cortisol (p = 0.047) differed between selected conditions when averaged across sampling times, possibly reflecting pre-existing differences, but BDNF did not differ (p = 0.559), and no time effects or condition × time interactions were observed. Conclusions: In this sample of 16 trained male Tier 2 players, effects were selective rather than global. Music and mindfulness were associated with lower post-condition mental effort, and mindfulness with greater ball involvement rather than improved technical efficiency, without evidence of differential pre-to-post biochemical responses; neither uniformly enhanced soccer-specific performance. Because the mental-fatigue induction was not statistically confirmed and multiple outcomes were tested, these acute findings are exploratory and associational.