O2 uptake kinetics above and below the lactic acidosis threshold during sinusoidal exercise

Philippe Haouzi, Y. Fukuba, R. Casaburi, W. Stringer, K. Wasserman

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Abstract

O2 uptake (V̇O2) kinetics at the onset of a constant work rate exercise are difficult to describe for work rates above the lactic acidosis threshold (LAT), because the steady-state level of V̇O2 response can usually not be identified. To describe the ability of the O2 transport system to deliver and the cells to utilize O2 above the LAT relative to that below the LAT, we applied a fluctuating (sinusoidal) variation of work rate. After 4 min of constant work at the midpoint of the sinusoidal work rate, a fluctuating work rate, at a period of 4 min, was applied below the LAT for the next 16 min. This was repeated in a range of work rates above the LAT with the same sine- wave amplitude. V̇O2 response appeared to follow a sinusoidal pattern similar to that of work rate for below- and above-LAT exercise. However, the amplitude of the V̇O2 response was significantly reduced (5.4 ± 2.6 vs. 7.6 ± 1.9 ml · min-1 · W-1, P < 0.01), and the phase lag increased above- compared with below-LAT work rate. V̇O2/heart rate fluctuations were dramatically reduced, whereas heart rate amplitude decreased and phase lag increased, for above-LAT sinusoidal work rate changes. These results suggest that V̇O2 kinetics are slowed in the work rate domain above the LAT relative to that below the LAT and that V̇O2 kinetics could be limited by the O2 transport mechanisms to the exercising muscle.

Original languageEnglish (US)
Pages (from-to)1683-1690
Number of pages8
JournalJournal of applied physiology
Volume75
Issue number4
DOIs
StatePublished - 1993

All Science Journal Classification (ASJC) codes

  • Physiology
  • Physiology (medical)

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