The VO2 response to exhaustive square wave exercise: influence of exercise intensity and mode

We investigated the oxygen uptake (O₂) response to exhaustive square wave exercise of approximately 2, 5 and 8 min duration in cycling and running. Nine males completed a ramp test and three square wave tests on a motorised treadmill and the same four tests on a cycle ergometer, throughout which gas exchange was assessed (Douglas bag method). The peak O₂ from the ramp test was higher for running than for cycling [mean (SD): 58.4 (2.8) vs. 55.9 (3.7) ml.kg^–1.min^–1; P=0.04]. However O_2max (defined as the highest O₂ achieved in any of the four tests) did not differ between running and cycling [60.0 (2.9) vs. 58.5 (3.3) ml.kg^–1.min^–1; P=0.15]. The peak O₂ was similar (P>0.1) for the 5 and 8 min square wave tests [98.5 (1.8) and 99.2 (2.3) %O_2max for running; 97.0 (4.2) and 97.5 (2.0) %O_2max for cycling] but lower (P<0.001) for the 2-min test [91.8 (2.5) and 89.9 (5.5) %O_2max for running and cycling respectively]. O₂ increased over the final two 30-s collection periods of the 2-min test for cycling [O₂=0.18 (0.15) l.min^–1; P<0.01] but not running [O₂=0.00 (0.09) l.min^–1; P=0.98]. We conclude that in the aerobically fit the peak O₂ for square wave running or cycling at an intensity severe enough to result in exhaustion in approximately 2 min is below O_2max. In running, O₂ plateaus at this sub-maximal rate.