Muscle oxygenation and pulmonary gas exchange kinetics during cycling exercise on-transitions in humans.
Near-infrared spectroscopy (NIRS) was utilized to gain insights into the kinetics of oxidative metabolism during exercise transitions. Ten untrained young men were tested on a cycle ergometer during transitions from unloaded pedaling to 5 min of constant-load exercise below (<VT) or above (>VT) the ventilatory threshold. Vastus lateralis oxygenation was determined by NIRS, and pulmonary O2 uptake (Vo --> Vo2) was determined breath-by-breath. Changes in deoxygenated hemoglobin + myoglobin concentration Delta[deoxy(Hb + Mb)] were taken as a muscle oxygenation index. At the transition, [Delta[deoxy(Hb + Mb)]] was unmodified [time delay (TD)] for 8.9 +/- 0.5 s at <VT or 6.4 +/- 0.9 s at >VT (both significantly different from 0) and then increased, following a monoexponential function [time constant (tau) = 8.5 +/- 0.9 s for <VT and 7.2 +/- 0.7 s for >VT]. For >VT a slow component of Delta[deoxy(Hb + Mb)] on-kinetics was observed in 9 of 10 subjects after 75.0 +/- 14.0 s of exercise. A significant correlation was described between the mean response time (MRT = TD + tau) of the primary component of Delta[deoxy(Hb + Mb)] on-kinetics and the tau of the primary component of the pulmonary Vo2 on-kinetics. The constant muscle oxygenation during the initial phase of the on-transition indicates a tight coupling between increases in O2 delivery and O2 utilization. The lack of a drop in muscle oxygenation at the transition suggests adequacy of O2 availability in relation to needs.
Grassi
Bruno
B
Dipartimento di Scienze e Tecnologie Biomediche, School of Medicine, University of Milan, Milan, Italy. Bruno.Grassi@unimi.it
Pogliaghi
Silvia
S
Rampichini
Susanna
S
Quaresima
Valentina
V
Ferrari
Marco
M
Marconi
Claudio
C
Cerretelli
Paolo
P
D000328:Adult; D000465:Algorithms; D001642:Bicycling / Q000502:physiology; D001823:Body Composition / Q000502:physiology; D002245:Carbon Dioxide / Q000378:metabolism; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008297:Male; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D015656:Respiratory Mechanics / Q000502:physiology; D012885:Skinfold Thickness; D019265:Spectroscopy, Near-Infrared
D006454:Hemoglobins; D002245:Carbon Dioxide; C100003:deoxyhemoglobin