The Slow Component Of The Vo2 Response Is Explained By The Increase In Glycolytic Contribution

During severe intensity exercise, energy contribution from glycolysis leads to accumulation of intracellular H+ in the working muscles. This acidification results in decreased efficiency in the excitation-contraction coupling mechanism in the muscle cells, which decreases force production. Some studies have suggested that additional, progressive recruitment of glycolytic (type II) muscle fibers may be needed to maintain force production in constant power exercise which causes an increase in oxygen uptake over time (the VO2 slow component) after ~3 minutes. PURPOSE: The purpose of this study was to determine if the amplitude of the VO2 slow component is related to the glycolytic contribution, during constant power, severe intensity, cycling exercise. METHODS: Seven women and thirteen men (age 22 ± 3 y) performed three constant power, severe intensity, cycle ergometer tests (2.6 ± 0.6 W/kg), which were terminated by the investigators after either 3 min, 6 min, or 9 min, with the order of durations determined using randomization. The amplitude of the VO2 slow component (A′slow) was calculated using established methods. Glycolytic contribution was estimated from the peak post-exercise blood lactate concentration. Correlations between A′slow and glycolytic contribution were calculated for each exercise duration. RESULTS: The values for A′slow were 0.5 ± 0.2 mL/kg/min, 6 ± 3 mL/kg/min, and 8 ± 3 mL/kg/min, respectively. The values for glycolytic contribution were 21 ± 6 mL/kg, 28 ± 8 mL/kg, and 30 ± 9 mL/kg in the 3 min, 6 min, and 9 min tests, respectively. The two variables were weakly correlated in the 3 min tests (r = 0.22), but strongly correlated in the 6 min and 9 min tests (r = 0.73 and r = 0.82, respectively). CONCLUSION: The results suggest that the amplitude of the VO2 slow component is related to the glycolytic contribution in 6 min and 9 min of exercise. This relationship may be explained by an increased recruitment of glycolytic (type II) fibers to maintain force production, leading to the delayed increase in VO2, after ~3 min of exercise.