Metabolic demands of intense aerobic interval training in competitive cyclists

Purpose: To investigate the metabolic demands of a single session of intens e aerobic interval training in highly trained competitive endurance cyclist s. Methods: Seven cyclists (peak O-2 uptake [(V) over dot O-2peak] 5.14 +/- 0.23 L.min(-1), mean +/- SD) performed 8 x 5 min work bouts at 86 +/- 28 o f (V) over dot O-2peak with 60-s recovery. Muscle biopsies were taken from the vastus lateralis immediately before and after the training session, whe reas pulmonary gas exchange and venous blood were sampled at regular interv als throughout exercise. Results: Muscle glycogen concentration decreased f rom 501 +/- 91 to 243 +/- 51 mmol.kg(-1) dry mass (P < 0.01). High rates of total carbohydrate oxidation were maintained throughout exercise (340 <mu> mol.kg(-1).min(-1)), whereas fat oxidation increased from 16 +/- 8 during t he first to 25 +/- 13 mu mol.kg(-1).min(-1) during the seventh work bout (P < 0.05). Blood lactate concentration remained between 5 and 6 mM throughou t 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). Alt hough muscle pH decreased from 7.09 +/- 0.06 at rest to 7.01 +/- 0.03 at th e end of the session (P < 0.01), blood pH was similar after the first and s eventh work bouts (7.34). Arterial oxygen saturation (%SpO(2)) 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 powe r outputs that are associated with high rates of glycogenolysis and total e nergy expenditure similar to those experienced during a 60-min competitive ride.