Muscle O2 uptake kinetics in humans: implications for metabolic control

• DOI: 10.1152/jappl.1996.80.3.988
• Publication Date: 2017-12-22T01:31:16Z
• Authors: B. Grassi; D. C. Poole; R. S. Richardson; D. R. Knight; B. K. Erickson; P. D. Wagner
• Keywords: Adult; Male; Oxygen; Kinetics; 03 medical and health sciences; Time Factors; 0302 clinical medicine; Muscles; Humans; Exercise; Blood Flow Velocity

Muscle O2 uptake (VO2) kinetics in response to an augmented energetic requirement (on-transition) has never been directly determined humans. We have developed a constant-infusion thermodilution technique that allowed rapid measurements of leg blood flow (Qleg) and, conjunction with frequent serial measurement arteriovenous content difference across the [(Ca - Cv)O2leg], permitted determination VO2 (VO2leg) at 3- 4-s time intervals. VO2leg during on-transition was taken as close approximation muscle (VO2mus) kinetics. Alveolar (VO2A), Qleg, delivery [(Q.CaO2leg)], (Ca Cv)O2leg, and were six trained subjects [age 22.8 +/- 4.4 (SD) yr; maximal 59.1 5.3 ml.kg-1.min-1] transition from unloaded pedaling workload (loaded pedaling; LP) (183 20 W) well below previously ventilatory threshold. For all variables, two distinct phases recognized. During first 10-15 s loaded (phase I), VO2A, (Q.CaO2)leg increased rapidly, whereas only slightly Cv)O2leg actually decreased. After phase I, variables showed monoexponential increase II), similar courses [slightly faster for CV)O2leg]. In consideration both phases, half times responses among not significantly different: 25.5 2.6 26.6 7.6 26.9 8.3 (Q.CaO2leg, 23.5 1.3 27.9 5.7 VO2leg. conclude VO2A VO2leg, measured by these methods, are similar. The analysis early (first s) indicates bulk working muscles is limiting However, present results cannot discriminate between maldistribution flow/VO2 vs. inertia intracellular oxidative machinery factor.