Maximal aerobic speed: methodological implications and unintended consequences

Maximal aerobic speed (MAS) represents the minimal speed where a further increase in speed will not result in a further increase in oxygen consumption (V̇O₂). MAS is determined from the relationship between maximal V̇O₂ (V̇O_2max) and running economy, the latter also expressed as the O₂ cost of running. There is no standardized method for determination of MAS in the literature, but three approaches are more dominant: the first approach consists of determining a loss of linearity between V̇O₂ and speed. The second approach performs a linear extrapolation from the relationship between submaximal V̇O₂ and speed towards V̇O_2max. The third approach divides V̇O_2max by the O₂ cost of running measured over one or more speeds. We explore the assumptions and flaws of the different approaches. We show that the first approach lacks sufficient objectivity. The second approach, based on linear extrapolation, is prone to significant error, particularly when changes in O₂ cost happen at the lower or higher speeds tested, to the extent that higher sub-maximal V̇O₂ for a given speed results in improved MAS and vice-versa. We suggest that MAS should be assessed using a simple division of V̇O_2max by the O₂ cost of running determined from a race-relevant speed, which can be easily integrated into a single testing session.