Plateauing of Oxygen Intake

I have read with interest the recent article of Gordon and colleagues [1]; they reported a positive relationship between the attainment of a maximal oxygen intake plateau and the magnitude of the individual's anaerobic capacity, as estimated from a maximally accumulated oxygen deficit. In support of their finding that only 4 of 9 fit young male cyclists reached their definition of an oxygen consumption plateau, Gordon et al. cited 3 earlier reports where only a small proportion of subjects reached a plateau. They also commented that other investigators had achieved a success rate as high as 91%, but they failed to cite findings from the definitive WHO/IBP international working party [2]. This consensus study developed an agreed protocol for maximal oxygen intake tests, demonstrating consistent plateauing in 24 young men when they each performed repeated tests over a 5-week period.

Reasons why a low proportion of oxygen consumption plateaus were observed in some earlier reports include an inappropriate choice of ergometer or test protocol (in particular, some observers have begun a ramp test at far too low a work rate), and the testing of unfit, poorly motivated subjects. The subjects of Gordon et al. were well-trained, and as experienced cyclists they were tested on a suitable type of ergometer; nevertheless, the initial power output of 120 W was undesirably low for fit young men, and in some individuals the time to voluntary exhaustion (range 8–17 min) exceeded the recommended ceiling. However, the main explanation of their findings seems to be their primary criterion of an oxygen consumption plateau. The text speaks of an increment in oxygen consumption of less than 50 ml/min, 3 times smaller than the universally accepted alternatives of 150 ml/[kg.min] or 2 ml/[kg.min], and probably outside the detection threshold of their automated metabolic measurement system. I found their Figure 1 a little hard to understand, but it appears to show that the oxygen consumption of all 9 subjects changed by less than 5 ml/min during the final minute of exercise.

It is difficult to assess the impact of inter-individual differences of motivation upon the reported data; Gordon et al. suggest that RER, heart rate and RPE values were comparable between those subjects who reached a plateau and those who did not. However, if the best motivated individuals were those who reached an oxygen consumption plateau, then I suspect that they would also have had the motivation to push themselves to a larger maximal oxygen deficit.

References

• 1 Gordon D, Hopkins S, King C, Keller D, Barnes RJ. Influence of the plateau at VO_2max is dependent on the anaerobic capacity.  Int J Sports Med. 2011;  32 1-6
• 2 Shephard RJ, Allen C, Benade AJS, Davies CTM, diPrampero PE, Hedman R, Merriman JE, Myhre K, Simmons R. The maximum oxygen intake: An international reference standard of cardiorespiratory fitness.  Bull World Health Organ. 1968;  38 757-764

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