Oxygen uptake kinetics and biological age in relation to pulling force and 400-m front crawl performance in young swimmers

Background: The study aimed to assess differences in the biological age (BA) of 13-year-old swimmers and show their ability, as biologically younger—late mature or older—early mature, to develop fast 60-s oxygen uptake ( [Formula: see text] ) kinetics and tethered swimming strength. Furthermore, the interplay between swimming strength, [Formula: see text] , and 400-m front crawl race performance was examined. Methods: The study involved 36 competitive young male swimmers (metrical age: 12.9 ± 0.56 years). Depending on BA examination, the group was divided into early-mature (BA: 15.8 ± 1.18 years, n = 13) and late-mature (BA: 12.9 ± 0.60 years, n = 23) participants, especially for the purpose of comparing tethered swimming indices, i.e., average values of force (F (ave)) and [Formula: see text] (breath-by-breath analysis) kinetic indices, measured simultaneously in 1-min tethered front crawl swimming. From the 400-m racing stroke rate, stroke length kinematics was retrieved. Results: In the 1-min tethered front crawl test, early-mature swimmers obtained higher results of absolute values of [Formula: see text] and F (ave). Conversely, when [Formula: see text] was present relatively to body mass and pulling force (in ml∙min(–1)∙kg(–1)∙N(−1)), late-mature swimmers showed higher [Formula: see text] relative usage. Late-mature swimmers generally exhibited a slower increase in [Formula: see text] during the first 30 s of 60 s. [Formula: see text] , F (ave), BA, and basic swimming kinematic stroke length were significantly interrelated and influenced 400-m swimming performance. Conclusion: The 1-min tethered swimming test revealed significant differences in the homogeneous calendar age/heterogeneous BA group of swimmers. These were distinguished by the higher level of [Formula: see text] kinetics and pulling force in early-mature individuals and lower efficiency per unit of body mass per unit of force aerobic system in late-mature peers. The higher [Formula: see text] kinetics and tethered swimming force were further translated into 400-m front crawl speed and stroke length kinematics.