Background: 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. Methods: 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. Results: Significant post-race increases in lactate levels (p < 0.05) and RPE (p < 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 (p = 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. Conclusions: Lactate accumulation and perceived exertion were the most sensitive indicators of fatigue (both p < 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.

(1) Background: This study analyzed the effects of intervention programs conducted between 2021 and 2025 as part of the “Aula UCLM-FNCLM” initiative—a partnership between a regional swimming federation and the university—on psychosocial factors in trained swimmers. This program presents interventions for swimmers, their coaches, their families, and their sports environment. (2) Methods: The effects of a 4-year intervention program on the Castilla-La Mancha swimming team, classified as Tier 3 (Tier 3: Highly Trained/National Level), according to the McKay classification framework (2021 team with 55 swimmers, 25 men, and 30 women; 17.3 ± 5.3 years), and the same sample in 2025 (42 swimmers, 19 men, 23 women—17 ± 2.8 years—and 11 dropouts). A self-perception questionnaire on performance in sport (CAED) was used. (3) Results: The results showed higher ratings (p < 0.001, η² = 0.30) from the swimmers of the 2025 CLM team in the coach factor, and moderate changes in the roles played by family (p < 0.05, η² = 0.12) and environment (p < 0.05, η² = 0.11). The only factor that did not improve was personal characteristics. (4) Conclusions: The UCLM-FNCLM program has contributed to improving the role of factors related to performance in sport (coach, family, and sports environment) in a cohort of regional-based swimmers.

Background: Acute exposure to moderate altitude may modify physiological responses to exercise, yet its effects on neuromuscular function and repeated-sprint performance in highly trained swimmers remain unclear. This study compared the acute effects of moderate altitude and normoxia during the same training protocol. Methods: A quasi-experimental repeated-measures design was employed, with six highly trained swimmers completing testing sessions under both normoxic and moderate-altitude conditions, separated by 1 week. Peripheral oxygen saturation (SpO₂), heart rate (HR), countermovement jump (CMJ), squat jump (SJ), rating of perceived exertion (RPE), blood lactate concentration ([La⁻]), and repeated-sprint swimming performance (4 × 50 m) were assessed. Results: SpO₂ was lower at altitude than in normoxia (p < 0.001, ηp² = 0.915), while HR showed a condition × time interaction (p = 0.007, ηp² = 0.391). CMJ, SJ, RPE, and [La⁻] did not differ between conditions. Sprint performance declined across repetitions for 15 m and 25 m splits (p ≤ 0.002), but no altitude effect or altitude × repetition interaction was observed for any performance measure (p > 0.18). Conclusion: Acute moderate-altitude exposure induced physiological changes, particularly reduced SpO₂, without impairing neuromuscular function, perceived exertion, lactate responses, or repeated-sprint swimming performance.

Altitude training is widely used in elite swimming, although its effects on sleep and acclimatisation remain insufficiently understood. The aim of this study was to describe changes in sleep difficulty, physiological acclimatisation, athlete-reported outcomes, and haematological markers during a 21-day altitude training camp (2320 m), and to explore the association between chronotype and sleep difficulty. Seven world-class swimmers (4 men, 3 women) were monitored before, during, and after altitude exposure. Sleep difficulty was assessed using the Athlete Sleep Screening Questionnaire, while daily monitoring included resting oxygen saturation, resting heart rate, acute mountain sickness symptoms, fatigue, recovery, hydration status, and training load. Chronotype was determined using the Morningness-Eveningness Questionnaire. Sleep difficulty was descriptively higher during the first week at altitude (6.14 ± 1.07 vs. 4.14 ± 1.21 at baseline) and returned towards baseline by week 3 (4.29 ± 1.50), although pairwise comparisons did not remain significant after multiplicity correction. Strong inverse associations between chronotype and sleep difficulty were observed at baseline (rho = −0.87, p = 0.014) and week 1 (rho = −0.85, p = 0.019), but neither met the Bonferroni-adjusted significance threshold (α = 0.010). SpO₂ increased across the camp, with week 3 significantly higher than weeks 1 and 2 after Bonferroni correction, whereas RHR was significantly lower in week 3 than in week 1, but not week 2, after correction. Athlete-reported outcomes remained stable, acute mountain sickness symptoms were minimal, and haematological and iron-status markers showed no significant pre-to-post changes. Sleep difficulty showed a transient descriptive increase during the initial phase of the altitude camp, while SpO₂ and RHR changes were consistent with physiological acclimatisation. Chronotype-related differences in sleep difficulty appeared to be present before altitude exposure rather than emerging specifically during the camp. Given the small sample size, these findings should be considered exploratory and hypothesis-generating.

Background: This study aimed to identify the field-based technical and biomechanical variables that best discriminate and predict competitive performance in 11–12-year-old swimmers. Methods: Seventy-two federated swimmers were assessed during a controlled technical evaluation session conducted four weeks prior to the Under-13 (U–13) Regional Championship. Variables measured included 25 m freestyle time and velocity, 25 m kick time and velocity, turn time and velocity using the 5 m in–5 m out criterion, stroke count, stroke length, and swimming efficiency index. Aqua Points were obtained from official championship results held one month after testing. Swimmers were categorized into three performance groups according to Aqua Points classification: low, medium, and high competitive level. A multiple linear regression analysis was performed to identify predictors of competitive performance. Results: Significant differences were observed between competitive levels for 25 m freestyle time and velocity, kick performance, turn time and velocity, and swimming efficiency (p < 0.05), with progressive improvements as Aqua Points increased. Significant differences were also observed for stroke count and stroke length, suggesting that stroke mechanics contributed to performance differentiation within this age group. In the regression analysis, 25 m freestyle velocity and turn velocity emerged as the strongest predictors of competitive performance, while sex was a significant covariate. The final model explained a large proportion of the variance in Aqua Points (R² = 0.846, adjusted R² = 0.832, p < 0.001). Conclusions: Competitive level in 11–12-year-old swimmers is strongly associated with technical proficiency, particularly short-distance swimming speed and turn execution. These findings highlight the importance of technical development during formative stages and provide practical insights for coaching strategies.

Purpose: This study prospectively monitored changes in repeated-sprint swimming performance, blood lactate ([La]) concentration, and countermovement-jump (CMJ) performance during a 6-month training period with traditionally periodized endurance training in competitive swimmers. Methods: Twenty well-trained sprint and middle-distance swimmers (mean [SD]; age = 18 [2] y, body mass = 69.6 [8.0] kg, height = 179 [6.1] cm) underwent body-composition assessment and completed a 7 × 50-m repeated-sprint test, with measurements of [La] and CMJ, before (October, preparation period) and after (April, early-competition period) a 6-month training period using traditional periodization. Results: There were no significant improvements in swimming velocity, CMJ height, or changes in [La] from October to April, with considerable individual variation. However, there was a small but significant increase in fat-free mass (mean difference ± SD: 0.9 ± 2.2 kg), albeit with a small effect size, and no changes in body fat or body mass. Significant and expected decreases in performance (swimming and CMJ) across the repetitions of the 7 × 50-m repeated-sprint tests were observed, accompanied by increases in [La], all with large effect sizes, but there was no evidence that training affected these results (no significant interactions). Conclusion: A 6-month training period with traditionally periodized endurance training failed to significantly improve repeated-sprint swimming performance, [La] response, or CMJ height in trained swimmers across the 2 training phases.