Purpose: To compare the dynamics of maximal oxygen uptake (V.O2), blood lactate ([La]b), total energy expenditure (Etot), and contributions of the aerobic (Eaer), alactic anaerobic (Ean,al), and lactic anaerobic (Ean,lac) metabolic energy pathways over 4 consecutive 25-m laps (L0-25, L25-50, etc) of a 100-m maximal freestyle swim. Methods: Elite swimmers comprising 26 juniors (age=16 [1] y) and 23 seniors (age=24 [5] y) performed 100 m at maximal speed and then 3 trials (25, 50, and 75 m) at the same pace as that of the 100 m. [La]b was collected, and V.O2 was measured 20 s postexercise. Results: The estimated energetic contributions for the 100-m trial are presented as mean (SD): Eaer, 51% (8%); Ean,al, 18% (2%); Ean,lac, 31% (9%). V.O2increased from L0-25 to L25-50 (mean=3.5 L/min; 90% confidence interval [CI], 3.4-3.7 5 L/min to mean=4.2 5 L/min; 90% CI, 4.0-4.3 5 L/min) and then stabilized in the 2nd 50 m (mean=4.1 L/min; 90% CI, 3.9-4.3 L/min to mean =4.2 5 L/min; 90% CI, 4.0-4.4 L/min). Etot (juniors, 138 [18] kJ; seniors, 168 [26] kJ), Ean,al (juniors, 27 [3] kJ; seniors, 30 [3] kJ), and Ean,lac (juniors, 38 [12] kJ; seniors, 62 [24] kJ) were 11-58% higher in seniors. Faster swimmers (n=26) had higher V.O2 (4.6??5 L/min V.O2 (4.65 L/min, 90% CI 4.4-4.8 5 L/min, 90% CI 3.6-4.2 5 L/min), and Eaer power was associated with fast performances (P<.001). Conclusion: Faster swimmers were characterized by higher V?O2and less time to reach the highest V.O2 at ?50 m of the 100-m swim. Anaerobic qualities become more important with age.
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