THE OXYGEN UPTAKE-POWER REGRESSION IN CYCLISTS AND UNTRAINED MEN - IMPLICATIONS FOR THE ACCUMULATED OXYGEN DEFICIT

The regression of oxygen uptake (VO2) on power output and the O-2 dema nd predicted for supra-peak oxygen uptake (VO2peak) exercise (power ou tput = 432 W) were compared in ten male cyclists [C, mean VO2peak = 67 .9 (SD 4.2) ml . kg(-1). min(-1)] and nine active, yet untrained men [ UT, mean VO2peak = 54.1 (SD 6.5) ml . kg(-1). min(-1)]. The VO2-power regression was determined using a continuous incremental cycle test (C ON4), performed twice, which comprised several 4-min exercise periods progressing in intensity from approximately 40%-85% VO2peak. Minute ve ntilation (V-E), heart rate (HR), respiratory exchange ratio (R), bloo d lactate concentration ([la(-)]b) and rectal temperature (T-re) were measured at rest and during CON4. The slope of the VO2-power regressio n was greater (P less than or equal to 10.05) 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 r esult, the O-2 demand (at 432 W) was also higher (P less than or equal to 0.05) in C [5.97 (SD 0.23) 1 . min(-1)] than UT [5.70 (SD 0.15) 1 . min(-1)]. Exercise R and [1a(-)](b) were lower (P less than or equal to 0.05) in C in comparison to UT at all power outputs, whereas V-E a nd HR were relatively lower (P less than or equal to 0.05) in C at pow er outputs approximating 180 W, 220 W and 270 W. Differences in fat me tabolism estimated over the first three power outputs accounted for ap proximately 19% of the difference in VO2-power slopes between the grou ps and up to 46% of the difference in VO2 at a given intensity. Althou gh the VO2-power regressions were linear for C [r = 0.997 (SD 0.001)] and UT [r = 0.997 (SD 0.001)], the VO2-power slope was higher at power outputs at or above the lactate threshold (13.2 ml . min(-1). W-1) th an 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 VO2 at the hig hest power outputs completely abolished the difference in VO2-power sl opes between C and UT. Thus, the relatively higher VO2 during incremen tal exercise in C can be almost entirely attributed to the higher O-2 cost of cycling at higher power outputs. In addition, the presence of non-linear responses in VO2 at higher intensities also confirms the in validity of describing the VO2 response across a wide range of power o utputs using a linear function, and challenges the validity of predict ing the O-2 demand of more intense exercise by a linear extrapolation of this same function.