title: Ventilation and blood lactate increase exponentially during incremental exercise.
abstract: This study examined whether the ventilatory (V) compensation for metabolic acidosis with increasing O2 uptake (VO2) and CO2 output (VCO2) might be more in accord with the theoretical expectation of a progressive acceleration of proton production from carbohydrate oxidation rather than a sudden onset of blood lactate (BLa) accumulation. The interrelationships between V, VO2, VCO2 and BLa concentration, [BLa], were investigated in 10 endurance-trained male cyclists during incremental (120 +/- 15 W min-1) exercise tests to exhaustion. Regression analyses on the V, VCO2 and [BLa] vs VO2 data revealed that all were better fitted by continuous Y = A.exp.[B.VO2] + C rate laws than by threshold linear rate equations (P < 0.0001). Plots of V vs VCO2 and [BLa] were also non-linear. Ventilation increased as an exponential V = 27 +/- 4.exp.[0.37 +/- 0.03.VCO2] function of VCO2 and as a hyperbolic function of [BLa]. In opposition to the 'anaerobic (lactate) threshold' hypothesis, we suggest these data are more readily explained by a continuous development of acidosis, rather than a sudden onset of BLa accumulation, during progressive exercise.
authors.affiliation: Department of Physiology, University of Cape Town Medical School, Observatory, South Africa.
authors.forename: S C
authors.initials: SC
authors.lastname: Dennis
authors.forename: T D
authors.initials: TD
authors.lastname: Noakes
authors.forename: A N
authors.initials: AN
authors.lastname: Bosch
mesh_terms: D000138:Acidosis / Q000378:metabolism; D000328:Adult; D002245:Carbon Dioxide / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D007773:Lactates / Q000097:blood*; D019344:Lactic Acid; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology; D012119:Respiration / Q000502:physiology*
chemical_list: D007773:Lactates; D002245:Carbon Dioxide; D019344:Lactic Acid