Dmax-derived lactate-threshold intensity profiles and associated factors in adolescent swimmers: a multicenter cross-sectional study

Objective To identify data-driven Dmax-derived threshold-intensity profiles in adolescent swimmers by jointly considering pool-based and land-based incremental-test indicators and to examine hematological, performance-related, maturation-related, and psychoperceptual characteristics associated with profile membership. Methods This multicenter cross-sectional study included 247 adolescent swimmers from three training centers. Participants completed a land-based cycling incremental test and a pool-based 5 × 200 m front-crawl incremental test. Pool-based Dmax-derived threshold intensity was expressed as swimming velocity at the Dmax point relative to event-specific personal-best velocity, whereas land-based Dmax-derived threshold power was expressed as cycling power output at the Dmax point. The two indicators were entered into latent profile analysis. Between-profile comparisons incorporated effect sizes, 95% confidence intervals, and Benjamini–Hochberg adjustment for multiple testing. Candidate variables were selected according to prior evidence and biological plausibility, screened for strong pairwise correlations, and entered into a multinomial logistic regression model with study center included as a categorical fixed effect. Results Three ordered threshold-intensity profiles were identified: lower (n = 117, 47.4%), intermediate (n = 72, 29.2%), and higher (n = 58, 23.5%). The selected model showed good classification accuracy (entropy = 0.929). Relative to the lower profile, membership in the intermediate profile was associated with a higher red blood cell count (OR = 7.765, 95% CI: 3.198–18.849), lower perceived exertion (OR = 0.500, 95% CI: 0.372–0.672), and greater last-repetition completion relative to personal-best velocity (OR = 1.725, 95% CI: 1.317–2.259). Membership in the higher profile was associated with a higher red blood cell count (OR = 40.412, 95% CI: 10.844–150.605), lower perceived exertion (OR = 0.300, 95% CI: 0.197–0.457), greater last-repetition completion (OR = 2.903, 95% CI: 2.007–4.200), lower mental fatigue (OR = 0.954, 95% CI: 0.916–0.993), and greater sport mental toughness (OR = 1.134, 95% CI: 1.041–1.235). Conclusions Adolescent swimmers exhibited three data-driven, ordered patterns in the joint distribution of pool-based Dmax intensity and land-based Dmax power. Profile membership was associated with concurrent hematological, performance-related, and psychoperceptual characteristics. These profiles provide an exploratory person-centered framework for describing cross-modal threshold-intensity heterogeneity rather than biologically discrete phenotypes or prescriptive training categories. Their reliability, longitudinal stability, and responsiveness to training require further evaluation.