The VO2 response for an exhaustive treadmill run at 800-m pace: a breath-by-breath analysis.

Recent research in which data were averaged over 10 or 30 s suggests that the VO(2) response of aerobically fit individuals plateaus below VO(2 max) in an exhaustive square-wave run lasting approximately 2 min. To investigate this phenomenon we examined the breath-by-breath VO(2) response of trained runners to an exhaustive treadmill run at 800 m pace. Eight male competitive runners completed two treadmill tests on separate days: a ramp test to exhaustion and an exhaustive square-wave run at 800-m pace. For the ramp test, the breath-by-breath data were smoothed with a 15-s moving average and the highest of the smoothed values was taken as VO(2 peak) [mean (SD): 68.9 (5.6) ml kg(-1) min(-1)]. For the square-wave, the breath-by-breath data were interpolated to give one value per second and modelled using a monoexponential function. Following a delay of 11.2 (1.5) s, VO(2) increased quickly [phase-2 time constant of 10.7 (2.7) s] towards an asymptote that represented just 85 (6)% of VO(2 peak) from the ramp test. Expressed in ml kg(-1) min(-1), this asymptote was independent of VO(2 peak) (r=0.04, P=0.94). However, as a percentage of VO(2 peak) it was negatively correlated with VO(2 peak) itself (r=-0.96, P<0.001). It is concluded that in an exhaustive square-wave treadmill run lasting approximately 2 min the VO(2) of aerobically fit runners increases quickly to plateau at a level that is lower than, but independent of, VO(2max).