| Abstrakt: |
Abstract: a1_In this experiment we studied the effect of different pedalling rates during cycling at a constant power output (PO) 132±31 W (mean±S.D.), corresponding to 50 % V02 max, on the oxygen uptake and the magnitude of the slow component of VO2 kinetics in humans. The PO corresponded to 50 % of V02 max, established during incremental cycling at a pedalling rate of 70 rev.min-1. Six healthy men aged 22.2 ±2.0 years with VO2 max 3.89 ±0.92 l.min-1, performed on separate days constant PO cycling exercise lasting 6 min at pedalling rates 40, 60, 80, 100 and 120 rev.min-1, in random order. Antecubital blood samples for plasma lactate [La]pi and blood acid-base balance variables were taken at 1 min intervals. Oxygen uptake was determined breath-by-breath. The total net oxygen consumed throughout the 6 min cycling period at pedalling rates of 40, 60, 80, 100 and 120 rev.min-1 amounted to 7.727± 1.197, 7.705± 1.548, 8.679± 1.262, 9.945± 1.435 and 13.720± 1.862 1, respectively for each pedalling rate. The VO2 during the 6 min of cycling only rose slowly by increasing the pedalling rate in the range of 40-100 rev.min-1. This increase, was 0.142 1 per 20 rev.min-1 on the average. Plasma lactate concentration during the sixth minute of cycling changed little within this range of pedalling rates: the values were 1.83 ±0.70, 1.80 ± 0.48, 2.33 ±0.88 and 2.52 ±0.33 mmoLl-1. The values of [La]pi reached in the 6th minute of cycling were not significantly different from the pre-exercise levels. Blood pH was also not affected by the increase of pedalling rate in the range of 40-100 rev.min-1. However, an increase of pedalling rate from 100 to 120 rev.min-1 caused a sudden increase in the VO2 amounting to 0.747 1 per 20 rev.min-1, accompanied by a significant increase in [La]pj from 1.21 ±0.26 mmol.l-1 in pre-exercise conditions to 5.92±2.46 mmol.l-1 reached in the 6th minute of cycling (P<0.01). |
