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 ($\dot{V}$ O₂) 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 ($\dot{V}$ O₂max), respectively, with 10 ​s between-bout rests (sequence R-BE-R-BE-R-BE-R). The $\dot{V}$ O₂ during the last BE ([52.2 ​± ​5.0] mL·kg⁻¹·min⁻¹) was significantly higher than the $\dot{V}$ O₂max 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 $\dot{V}$ O₂ during the AC ([39.2 ​± ​7.1] mL·kg⁻¹·min⁻¹ [6^th bout]) was significantly higher than the $\dot{V}$ O₂max of AC ([30.2 ​± ​4.4] mL·kg⁻¹·min⁻¹, n ​= ​7). With occlusion, the corresponding $\dot{V}$ O₂ ([29.8 ​± ​3.9] mL·kg⁻¹·min⁻¹) was reduced to that of the $\dot{V}$ O₂max of AC and significantly less than the $\dot{V}$ O₂ 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 $\dot{V}$ O₂ for the ongoing exercise plus excess post-oxygen consumption (EPOC) produced by the previous exercise with a higher $\dot{V}$ O₂max.