The Impact of Competitive Fatigue on Physiological Variables in National Level Youth Swimmers

<b>Background:</b> This study investigated the impact of competitive fatigue on physiological (blood lactate and heart rate [HR]), neuromuscular (countermovement jump [CMJ]), and psychological (rate of perceived exertion [RPE]) variables in youth swimmers. <b>Methods:</b> Forty-two swimmers (mean ± SD, 14 ± 0.5 years; height for boys: 1.73 ± 0.03 m, girls: 1.69 ± 0.02 m; body mass: 67 ± 2.8 kg for boys and 62 ± 2.8 kg for girls) participated during a four-day championship, with data collected before and after their competition heats. <b>Results:</b> Significant post-race increases in lactate levels (<i>p</i> < 0.05) and RPE (<i>p</i> < 0.05) were observed across all distances, particularly after the 100 m and 200+ m events. Heart rate showed a decrease after the 50 m event and an increase after longer distances, reflecting different recovery demands. Although CMJ performance decreased after the races, these changes were not statistically significant (<i>p</i> = 0.810). The findings underscore the importance of race distance in modulating fatigue responses and suggest that RPE and lactate are the most sensitive indicators of competition-induced stress in these youth swimmers. <b>Conclusions:</b> Lactate accumulation and perceived exertion were the most sensitive indicators of fatigue (both <i>p</i> < 0.01), while HR and CMJ responses exhibited variability depending on race distance. These findings highlight the practical use of lactate and RPE monitoring related to fatigue and recovery strategies during competitions in youth swimmers.