Ramadan intermittent fasting alters cardiac autonomic modulation, neuromuscular performance, and recovery in adolescent tennis players: a within-subject repeated-measures design

Background: Tennis requires repeated high-intensity efforts with brief recovery periods, placing significant demands on cardiac autonomic regulation and neuromuscular performance. Ramadan intermittent fasting alters sleep, nutrition, and hydration patterns, potentially affecting match responses, particularly in adolescents. Methods: Sixteen male International Tennis Federation (ITF) junior players completed a within-subject repeated-measures study during mid-Ramadan and 15 days post-Ramadan. Each performed a standardized two-set outdoor match under both conditions. Heart rate variability (HRV), countermovement jump (CMJ), blood glucose, hydration markers, and rating of perceived exertion were assessed at baseline (T0), between sets (T1), and post-match (T2). Sleepiness, chronotype, fatigue, and recovery were evaluated via validated questionnaires. Results: Match play reduced lnRMSSD (p < 0.001, ηp2 = 0.775) and increased LF/HF (p < 0.001, ηp2 = 0.234), indicating sympathetic dominance. During Ramadan, parasympathetic activity was lower (p < 0.001, ηp2 = 0.269), and CMJ performance was reduced (p = 0.010, ηp2 = 0.085). Blood glucose showed a Period × Set interaction (p = 0.020, ηp2 = 0.114). Sleepiness, fatigue, and perceived recovery were significantly impaired (p < 0.001). Conclusion: Ramadan intermittent fasting reduces vagal activity and impairs neuromuscular performance in adolescent tennis players. HRV-guided training, optimized nutrition, and sleep management may help mitigate these effects.