The purpose of the present study was to examine oxygen consumption (VO(2) ) kinetics during severe-intensity running exercise through a four-phase model that considered a decrease in VO(2) at the end of the exercise in light of previous research in which this decrease was only noticed. After determination of maximal oxygen consumption VO(2) max), thirteen highly trained males performed a square-wave running to exhaustion at approximately 95 % of VO(2) max on a level treadmill. VO(2) and ventilatory gas exchange variables were determined breath-by-breath. Computerised non-linear regression techniques incorporating exponential and linear terms were used to describe VO(2) and ventilatory gas exchange variable responses. In contrast with the classical 3-component model that describes the increase in VO(2) for severe-intensity exercise, we observed a 4(th) phase characterised by a significant decrease in VO(2) before exhaustion (slope of VO(2)-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 VO(2), 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 VO(2) and reduced V(E) remains to be explored.