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

We investigated the oxygen uptake (V.O-2) 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 V.O-2 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 V.O-2max (defined as the highest V.O-2 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 V.O-2 was similar (P>0.1) for the 5 and 8 min square wave tests [98.5 (1.8) and 99.2 (2.3) %V.O-2max for running; 97.0 (4.2) and 97.5 (2.0) %V.O-2max for cycling] but lower (P<0.001) for the 2-min test [91.8 (2.5) and 89.9 (5.5) %V.O-2max for running and cycling respectively]. V.O-2 increased over the final two 30-s collection periods of the 2-min test for cycling [DeltaV.O-2=0.18 (0.15) l.min(-1); P<0.01] but not running [DeltaV.O-2=0.00 (0.09) l.min(-1); P=0.98]. We conclude that in the aerobically fit the peak V.O-2 for square wave running or cycling at an intensity severe enough to result in exhaustion in approximately 2 min is below V.O-2max. In running, V.O-2 plateaus at this sub-maximal rate.