Abstract: Purpose: The presence of a maturational threshold that modulates children`s physiological responses to exercise training continues to be debated, not least due to a lack of longitudinal evidence to address this question. The purpose of this study was to investigate the interaction between swim-training status and maturity in nineteen trained (T, 10 ± 1 years, -2.4 ± 1.9 years pre-peak height velocity, 8 boys) and fifteen untrained (UT, 10 ± 1 years, -2.3 ± 0.9 years pre-peak height velocity, 5 boys) children, at three annual measurements. Methods: In addition to pulmonary gas exchange measurements, stroke volume (SV) and cardiac output ( ) were estimated by thoracic bioelectrical impedance during incremental ramp exercise. Results: At baseline and both subsequent measurement points, trained children had significantly (P < 0.05) higher peak oxygen uptake (year 1 T 1.75 ± 0.34 vs. UT 1.49 ± 0.22; year 2 T 2.01 ± 0.31 vs. UT 1.65 ± 0.08; year 3 T 2.07 ± 0.30 vs. UT 1.77 ± 0.16 l/min) and (year 1 T 15.0 ± 2.9 vs. UT 13.2 ± 2.2; year 2 T 16.1 ± 2.8 vs. UT 13.8 ± 2.9; year 3 T 19.3 ± 4.4 vs. UT 16.0 ± 2.7 l/min). Furthermore, the SV response pattern differed significantly with training status, demonstrating the conventional plateau in UT but a progressive increase in T. Multilevel modelling revealed that none of the measured pulmonary or cardiovascular parameters interacted with maturational status, and the magnitude of the difference between T and UT was similar, irrespective of maturational status. Conclusion: The results of this novel longitudinal study challenge the notion that differences in training status in young people are only evident once a maturational threshold has been exceeded.
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