Oxygen uptake during the last bouts of exercise incorporated into high-intensity intermittent cross-exercise exceeds the V_ O2max of the same exercise mode

Oxygen uptake(V O_(2))was measured during a non-exhaustive high-intensity intermittent cross-exercise(HIICE)protocol consisting of four alternating bouts of 20 s running(R)and three bouts of bicycle exercise(BE)at~160%and~170%maximal oxygen uptake(V O_(2)max),respectively,with 10 s between-bout rests(sequence R-BE-R-BER-BE-R).The V O_(2) during the last BE([52.2±5.0]mL⋅kg^(-1)⋅min^(-1))was significantly higher than the V O_(2)max of the BE([48.0±5.4]mL⋅kg^(-1)⋅min^(-1),n=30)and similar to that of running.For clarifying the underlying mechanisms,a corresponding HIICE-protocol with BE and arm cranking ergometer exercise(AC)was used(sequence AC-AC-BE-AC-BE-AC-AC-BE).In some experiments,thigh blood flow was occluded by a cuff around the upper thigh.Without occlusion,the V O_(2) during the AC([39.2±7.1]mL⋅kg^(-1)⋅min^(-1)[6th bout])was significantly higher than the V O_(2)max of AC([30.2±4.4]mL⋅kg^(-1)⋅min^(-1),n=7).With occlusion,the corresponding V O_(2)([29.8±3.9]mL⋅kg^(-1)⋅min^(-1))was reduced to that of the V O_(2)max of AC and significantly less than the V O_(2) without occlusion.These findings suggest that during the last bouts of HIICE may exceed the of the specific exercise,probably because it is a summation of the V O_(2) for the ongoing exercise plus excess post-oxygen consumption(EPOC)produced by the previous exercise with a higher V O_(2)max.