Collective case study on periodized training in elite female middle- and long-distance swimmers preparing for national competition

Background Elite swimmers increasingly face calendars requiring multiple performance peaks within a single season, a scenario for which traditional single-target periodization models may be insufficient. Methods This longitudinal collective case study followed five elite female middle- and long-distance freestyle swimmers across a 52-week macrocycle preparing for two national championships. The program combined three altitude camps, sea-level integration phases and two timed tapers. Training intensity distribution (TID) was quantified with a three-zone lactate-threshold model; hemoglobin, hematocrit, red blood cell count, creatine kinase and cortisol were measured at four time points; and performance was assessed by time-trial and official competition results. Given N = 5, analysis prioritized a smallest-worthwhile-change (SWC) classification for performance and paired effect sizes with 95% confidence intervals for blood markers rather than null-hypothesis significance testing. Hematological outcomes are concentration-based indices; training-load descriptors refer to in-water swimming only. Results Applying an SWC of ≈0.24% to the 20 athlete-by-event observations, 12/20 (60%) changes at Competition 1 and 18/20 (90%) at Competition 2 exceeded the SWC, most representing improvement over baseline; this ordering held across the full defensible range of reference variability (SWC 0.22–0.42%). Hematological effect sizes were largest at Week 27 (RBC: Hedges’ g = 2.32, 95% CI [0.64, 4.01]; HCT: g = 2.04 [0.50, 3.58]), while creatine kinase and cortisol peaked at Week 17 and were closer to baseline at Week 49, compatible with a lower physiological stress state at that sampled time point. TID shifted across phases (pyramidal during base development, polarized during altitude blocks, threshold-oriented during race-pace sharpening), with marked inter-individual heterogeneity in performance and physiological responses. Conclusion Across this double-peak macrocycle, most athlete-by-event changes exceeded the SWC, and the proportion doing so was higher at the second championship than at the first; these changes occurred alongside altitude-associated increases in concentration-based oxygen-transport indices and a taper-associated normalization of creatine kinase and cortisol. With no control group or randomization, only five athletes and four blood samples, several simultaneous interventions and unmeasured confounders (iron status, menstrual-cycle phase, dryland load), these findings describe associations only. They are offered as exploratory, hypothesis-generating observations from a single elite squad rather than as causal evidence.