Oxygen uptake kinetics during two bouts of heavy cycling separated by fatiguing sprint exercise in humans

International audienceWe tested the hypothesis that O 2 uptake (V˙o 2 ) kinetics at the onset of heavy exercise would be altered in a state of muscle fatigue and prior metabolic acidosis. Eight well-trained cyclists completed two identical bouts of 6-min cycling exercise at >85% of peak V˙o 2 separated by three successive bouts of 30 s of sprint cycling. Not only was baselineV˙o 2 elevated after prior sprint exercises but also the time constant of phase IIV˙o 2 kinetics was faster (28.9 ± 2.4 vs. 22.2 ± 1.7 s; P < 0.05). CO 2 output (V˙co 2 ) was significantly reduced throughout the second exercise bout. SubsequentlyV˙o 2 was greater at 3 min and increased less after this after prior sprint exercise. Cardiac output, estimated by impedance cardiography, was significantly higher in the first 2 min of the second heavy exercise bout. Normalized integrated surface electromyography of four leg muscles and normalized mean power frequency were not different between exercise bouts.V˙o 2 andV˙co 2 kinetic responses to heavy exercise were markedly altered by prior multiple sprint exercises