title: Effects of training on muscle O2 transport at VO2max.
abstract: To quantify the relative contributions of convective and peripheral diffusive components of O2 transport to the increase in leg O2 uptake (VO2leg) at maximum O2 uptake (VO2max) after 9 wk of endurance training, 12 sedentary subjects (age 21.8 +/- 3.4 yr, VO2max 36.9 +/- 5.9 ml.min-1.kg-1) were studied. VO2max, leg blood flow (Qleg), and arterial and femoral venous PO2, and thus VO2leg, were measured while the subjects breathed room air, 15% O2, and 12% O2. The sequence of the three inspirates was balanced. After training, VO2max and VO2leg increased at each inspired O2 concentration [FIO2; mean over the 3 FIO2 values 25.2 +/- 17.8 and 36.5 +/- 33% (SD), respectively]. Before training, VO2leg and mean capillary PO2 were linearly related through the origin during hypoxia but not during room air breathing, suggesting that, at 21% O2, VO2max was not limited by O2 supply. After training, VO2leg and mean capillary PO2 at each FIO2 fell along a straight line with zero intercept, just as in athletes (Roca et al. J. Appl. Physiol. 67: 291-299, 1989). Calculated muscle O2 diffusing capacity (DO2) rose 34% while Qleg increased 19%. The relatively greater rise in DO2 increased the DO2/Qleg, which led to 9.9% greater O2 extraction. By numerical analysis, the increase in Qleg alone (constant DO2) would have raised VO2leg by 35 ml/min (mean), but that of DO2 (constant Qleg) would have increased VO2leg by 85 ml/min, more than twice as much. The sum of these individual effects (120 ml/min) was less (P = 0.013) than the observed rise of 164 ml/min (mean). This synergism (explained by the increase in DO2/Qleg) seems to be an important contribution to increases in VO2max with training.
authors.affiliation: Department of Medicine, Hospital Clínic, Universitat de Barcelona, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Roca
authors.forename: A G
authors.initials: AG
authors.lastname: Agusti
authors.forename: A
authors.initials: A
authors.lastname: Alonso
authors.forename: D C
authors.initials: DC
authors.lastname: Poole
authors.forename: C
authors.initials: C
authors.lastname: Viegas
authors.forename: J A
authors.initials: JA
authors.lastname: Barbera
authors.forename: R
authors.initials: R
authors.lastname: Rodriguez-Roisin
authors.forename: A
authors.initials: A
authors.lastname: Ferrer
authors.forename: P D
authors.initials: PD
authors.lastname: Wagner
mesh_terms: D000222:Adaptation, Physiological; D000293:Adolescent; D000328:Adult; D001693:Biological Transport, Active; D004058:Diffusion; D015444:Exercise / Q000502:physiology; D005260:Female; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D008297:Male; D009132:Muscles / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*; D010806:Physical Education and Training; D010807:Physical Endurance / Q000502:physiology