The oxygen uptake-power regression in cyclists and untrained men: implications for the accumulated oxygen deficit

Abstract

The regression of oxygen uptake (O₂) on power output and the O₂ demand predicted for suprapeak oxygen uptake (O_2peak) exercise (power output = 432 W) were compared in ten male cyclists [C, mean O_2peak = 67.9 (SD 4.2) ml · kg⁻¹ · min⁻¹] and nine active, yet untrained men [UT, mean O_2peak = 54.1 (SD 6.5) ml · kg⁻¹ · min⁻¹]. The O₂-power regression was determined using a continuous incremental cycle test (CON4), performed twice, which comprised several 4-min exercise periods progressing in intensity from approximately 40%–85% O_2peak. Minute ventilation (_E), heart rate (HR), respiratory exchange ratio (R), blood lactate concentration ([1a⁻]_b) and rectal temperature (T _re) were measured at rest and during CON4. The slope of the O₂-power regression was greater (P ≤ 0.05) in C [12.4 (SD 0.7) ml · min⁻¹. W⁻¹] compared to UT [11.7 (SD 0.4) ml · min⁻¹ W⁻¹]; as a result, the O₂ demand (at 432 W) was also higher (P ≤ 0.05) in C [5.97 (SD 0.23) l · min⁻¹] than UT [5.70 (SD 0.15) 1 · min⁻¹]. ExerciseR and [la⁻]_b were lower (P ≤ 0.05) in C .in comparison to UT at all power outputs, whereas _E and HR were relatively lower (P ≤ 0.05) in C at power outputs approximating 180 W, 220 W and 270 W. Differences in fat metabolism estimated over the first three power outputs accounted for approximately 19% of the difference in O₂-power slopes between the groups and up to 46% of the difference in O₂ at a given intensity. Although the O₂-power regressions were linear for C [r = 0.997 (SD 0.001)] and UT [r = 0.997 (SD 0.001)], the O₂-power slope was higher at power outputs at or above the lactate threshold (13.2 ml · min⁻¹ · W⁻¹ than at lower intensities (11.6 ml · min⁻¹ · W⁻¹) in C, an effect which was less profound in UT. As a result, the exclusion of O₂ at the highest power outputs completely abolished the difference in O₂-power slopes between C and UT. Thus, the relatively higher O₂ during incremental exercise in C can be almost entirely attributed to the higher O₂ cost of cycling at higher power outputs. In addition, the presence of non-linear responses in O₂ at higher intensities also confirms the invalidity of describing the O₂ response across a wide range of power outputs using a linear function, and challenges the validity of predicting the O₂ demand of more intense exercise by a linear extrapolation of this same function.