Metabolic demands of intense aerobic interval training in competitive cyclists

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STEPTO, N. K., D. T. MARTIN, K. E. FALLON, and J. A. HAWLEY. Metabolic demands of intense aerobic interval training in competitive cyclists. Med. Sci. Sports Exerc., Vol. 33, No. 2, 2001, pp. 303–310. Purpose:To investigate the metabolic demands of a single session of intense aerobic interval training in highly trained competitive endurance cyclists. Methods :Seven cyclists (peak O2 uptake [O2peak] 5.14 ± 0.23 L.min−1, mean ±SD) performed 8 × 5 min work bouts at 86 ± 2% of O2peak with 60-s recovery. Muscle biopsies were taken from the vastus lateralis immediately before and after the training session, whereas pulmonary gas exchange and venous blood were sampled at regular intervals throughout exercise. Results :Muscle glycogen concentration decreased from 501 ± 91 to 243 ± 51 mmol·kg−1 dry mass (P < 0.01). High rates of total carbohydrate oxidation were maintained throughout exercise (340 μmol·kg−1·min−1), whereas fat oxidation increased from 16 ± 8 during the first to 25 ± 13 μmol·kg−1·min−1 during the seventh work bout (P < 0.05). Blood lactate concentration remained between 5 and 6 mM throughout exercise, whereas muscle lactate increased from 6 ± 1 at rest to 32 ± 12 mmol·kg−1 d.m. immediately after the training session (P < 0.01). Although muscle pH decreased from 7.09 ± 0.06 at rest to 7.01 ± 0.03 at the end of the session (P < 0.01), blood pH was similar after the first and seventh work bouts (7.34). Arterial oxygen saturation (%SPO2) fell to 95.6 ± 1% during the first work bout and remained at 94% throughout exercise: the 60-s rest intervals were adequate to restore %SPO2 to 97%. Conclusion :Highly trained cyclists are able to sustain high steady state aerobic power outputs that are associated with high rates of glycogenolysis and total energy expenditure similar to those experienced during a 60-min competitive ride.

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