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.

Purpose : To examine the association between time of day and performance across competition phases in Olympic swimming, considering scheduling structure and event distance. Methods : A total of 3510 performances from 705 swimmers across 6 Olympic Games (Athens 2004–Paris 2024) were analyzed using linear mixed-effects models. Time of day was entered as a continuous predictor, with competition phase (heats, semifinals, and finals), stroke, sex, Olympic year, and event distance as covariates, and swimmer identity as a random intercept. Interaction terms between time of day and competition phase were tested, and supplementary analyses compared Olympic editions with morning finals (Beijing 2008 and Tokyo 2020) versus evening finals. Results : Time of day was significantly associated with standardized performance overall ( β = −0.05, P < .001). A significant time-of-day × competition phase interaction showed that diurnal effects differed across rounds, being most pronounced during heats ( β = −0.055), attenuated during semifinals, and showing only a small positive trend in finals not confirmed in the finals only analysis. A finals-only model confirmed no significant association between time of day and standardized performance ( β = 0.04, P = .456). Olympic editions with morning-final schedules were associated with faster standardized performances than editions with evening-final schedules ( β = −0.27, P < .001), although this should be interpreted as an effect of competition scheduling and circadian adaptation rather than an intrinsic morning-performance advantage. Event distance did not consistently moderate diurnal patterns. Conclusions : Time-of-day effects in Olympic swimming are strongly modulated by competition phase and scheduling structure, being most detectable during heats and attenuated or masked in finals.

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.