Prevalence of cardio-respiratory factors in the occurrence of the decrease in oxygen uptake during supra-maximal, constant-power exercise.
OBJECTIVE
To investigate the physiological mechanisms that explain the end-exercise decrease in oxygen uptake [Formula: see text] during strenuous constant-power exercise, we recruited eleven trained, track cyclists.


METHODS
On two separated days they performed 1) resting spirometric measures, followed by an incremental test on a cycle ergometer to determine the power output at [Formula: see text] and 2) an exhaustive isokinetic supramaximal cycling exercise (Tlimsupra) at 185 ± 24% of [Formula: see text] (i.e., 640.5 ± 50.8 W). During cycling exercise tests, [Formula: see text], ventilation parameters, stroke volume (SV) and heart rate were continuously recorded. Furthermore, arterialised capillary blood samples were collected to measure blood pH, arterial oxygen saturation, lactate and bicarbonate concentration before and 5 min after Tlimsupra.


RESULTS
A > 5% decrease in [Formula: see text] and/or SV was observed in 6 subjects, with 5 out of 6 subjects presenting both phenomena. The magnitude of the [Formula: see text] decrease was correlated with the magnitude of the SV decrease (R = 0.75, P < 0.01), the peak-exercise end-tidal O2 partial pressure (R = 0.80, P < 0.005) and the resting, forced expiratory volume in 1 s (R = 0.72, P < 0.05), but not with any blood variables. The significant post-Tlimsupra decrease in forced vital capacity and forced inspiratory volume corroborate with a possible respiratory muscle fatigue.


CONCLUSIONS
Based on these findings, we demonstrate that the occurrence of [Formula: see text] decrease in more than half of our subjects, during a strenuous constant-power exercise leading to a mild-acidosis (pH = 7.21 ± 0.04), results mainly from cardio-respiratory factors and not from blood metabolic responses.
French National Institute of Sports (INSEP), Research Department, Laboratory of Sport, Expertise and Performance, 11 Tremblay Avenue, 75012 Paris, France.
Christine
C
Hanon
French National Institute of Sports (INSEP), Research Department, Laboratory of Sport, Expertise and Performance, 11 Tremblay Avenue, 75012 Paris, France ; Laboratory "Motricité, Interactions, Performance" (EA 4334), University of Nantes, F-44000 Nantes, France.
Sylvain
S
Dorel
French National Institute of Sports (INSEP), Research Department, Laboratory of Sport, Expertise and Performance, 11 Tremblay Avenue, 75012 Paris, France ; Laboratory "Motricité, Interactions, Performance" (EA 4334), University of Nantes, F-44000 Nantes, France.
Rémi
R
Delfour-Peyrethon
University of Picardie Jules Verne (EA-3300), 80025 Amiens cedex, France.
Pierre-Marie
PM
Leprêtre
Institute of Sport, Exercise and Active Living (ISEAL), and the College of Sport and Exercise Science, Victoria University, Melbourne, Australia.
David J
DJ
Bishop
Movement to Health (M2H), Montpellier-1 University, Euromov, Montpellier, France.
Stéphane
S
Perrey
French National Institute of Sports (INSEP), Research Department, Laboratory of Sport, Expertise and Performance, 11 Tremblay Avenue, 75012 Paris, France ; STAPS Department, University of Evry Val d'Essonne, François Mitterrand Boulevard, 91025 Evry, France.
Claire
C
Thomas
Acidosis; Cardio-respiratory parameters; High-intensity exercise; Oxygen consumption