The slow component of VO2 in professional cyclists.

OBJECTIVES: To analyse the slow component of oxygen uptake (VO2) in professional cyclists and to determine whether this phenomenon is due to altered neuromuscular activity, as assessed by surface electromyography (EMG).

METHODS: The following variables were measured during 20 minute cycle ergometer tests performed at about 80% of VO2MAX in nine professional road cyclists (mean (SD) age 26 (2) years; VO2max 72.6 (2.2) ml/kg/min): heart rate (HR), gas exchange variables (VO2, ventilation (VE), tidal volume (VT), breathing frequency (fb), ventilatory equivalents for oxygen and carbon dioxide (VE/VO2 and VE/VCO2 respectively), respiratory exchange ratio (RER), and end tidal PO2 and PCO2 (PETO2 and PETCO2 respectively)), blood variables (lactate, pH, and [HCO3-]) and EMG data (root mean from square voltage (rms-EMG) and mean power frequency (MPF)) from the vastus lateralis muscle.

RESULTS: The mean magnitude of the slow component (from the end of the third minute to the end of exercise) was 130 (0.04) ml in 17 minutes or 7.6 ml/min. Significant increases from three minute to end of exercise values were found for the following variables: VO2 (p<0.01), HR (p<0.01), VE (p<0.05), fb (p<0.01), VE/VO2 (p<0.05), VE/VCO2 (p<0.01), PETO2 (p<0.05), and blood lactate (p<0.05). In contrast, rms-EMG and MPF showed no change (p>0.05) throughout the exercise tests.

CONCLUSIONS: A significant but small VO2 slow component was shown in professional cyclists during constant load heavy exercise. The results suggest that the primary origin of the slow component is not neuromuscular factors in these subjects, at least for exercise intensities up to 80% of VO2MAX.