Decrease in Oxygen Uptake at the End of a High-Intensity Submaximal Running in Humans

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Abstract
The purpose of the present study was to examine oxygen consumption (V˙O2) kinetics during severe-intensity running exercise through a four-phase model that considered a decrease in V˙O2 at the end of the exercise in light of previous research in which this decrease was only noticed. After determination of maximal oxygen consumption (V˙O2max), thirteen highly trained males performed a square-wave running to exhaustion at ~95 % of V˙O2max on a level treadmill. V˙O2 and ventilatory gas exchange variables were determined breath-by-breath. Computerised non-linear regression techniques incorporating exponential and linear terms were used to describe V˙O2 and ventilatory gas exchange variable responses. In contrast with the classical 3-component model that describes the increase in V˙O2 for severe-intensity exercise, we observed a 4th phase characterised by a significant decrease in V˙O2 before exhaustion (slope of V˙O2-time relationship significantly different from a zero value, p < 0.01) in 7 out of 13 subjects. Following a time delay of 31 ± 44 s after the decrease in V˙O2, a significant decrease of minute ventilation (V˙E) was present for 6 of the 7 subjects (p < 0.02). During the exercise for the subjects who decreased V˙E, a reduction of 288 ± 169 ml in tidal volume was associated with an increase of 10.2 ± 2.4 min-1 in breathing frequency. These data suggest that the respiratory system might be stressed more for some endurance-trained athletes. The specific link between reduced V˙O2 and reduced V˙E remains to be explored.

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