Unit of oxygen uptake efficiency slope

抄録

The oxygen uptake efficiency slope (OUES) is the slope of a regression line of oxygen uptake (VO₂) on logarithmically converted minute ventilation (V_E) measured during incremental exercise: VO₂ = alog₁₀V_E + b. Here, a is the OUES. The higher the OUES, the more efficient the uptake of oxygen. The OUES has been widely accepted to estimate maximum oxygen uptake without maximal exercise. Nevertheless, the unit of OUES is unsettled in the literature having eight different descriptions. We introduced a new equation for the OUES using resting VO₂ (VO_{2 rest}) and resting V_E (V_{E rest}): VO₂ = alog₁₀(V_E/V_{E rest}) + VO_{2 rest}. This equation is based on the mathematical principle that an antilogarithm such as V_E/V_{E rest} is dimensionless. It is clear from this equation that OUES has the same unit as VO₂, because log₁₀(V_E/V_{E rest}) is just a numerical value without the unit. The new equation is written as VO₂ = alog₁₀V_E - alog₁₀V_{E rest} + VO_{2 rest}, where b = - alog₁₀V_{E rest} + VO_{2 rest}. The OUES value is obtained from Baba’s original equation with VO₂ and V_E during incremental exercise. The new equation is useful to identify the unit of OUES and the y-intercept b.