The present study intended to verify if the inclusion of intensities above lactate threshold (LT) in the VO₂/running speed regression (RSR) affects the estimation error of accumulated oxygen deficit (AOD) during a treadmill running performed by endurance-trained subjects. Fourteen male endurance-trained runners performed a sub maximal treadmill running test followed by an exhaustive supra maximal test 48h later. The total energy demand (TED) and the AOD during the supra maximal test were calculated from the RSR established on first testing. For those purposes two regressions were used: a complete regression (CR) including all available sub maximal VO₂ measurements and a sub threshold regression (STR) including solely the VO₂ values measured during exercise intensities below LT. TED mean values obtained with CR and STR were not significantly different under the two conditions of analysis (177.71 ± 5.99 and 174.03 ± 6.53 ml·kg^-1, respectively). Also the mean values of AOD obtained with CR and STR did not differ under the two conditions (49.75 ± 8.38 and 45.8 9 ± 9.79 ml·kg^-1, respectively). Moreover, the precision of those estimations was also similar under the two procedures. The mean error for TED estimation was 3.27 ± 1.58 and 3.41 ± 1.85 ml·kg^-1 (for CR and STR, respectively) and the mean error for AOD estimation was 5.03 ± 0.32 and 5.14 ± 0.35 ml·kg^-1 (for CR and STR, respectively). The results indicated that the inclusion of exercise intensities above LT in the RSR does not improve the precision of the AOD estimation in endurance-trained runners. However, the use of STR may induce an underestimation of AOD comparatively to the use of CR.

• It has been suggested that the inclusion of exercise intensities above the lactate threshold in the VO/power regression can significantly affect the estimation of the energy cost and, thus, the estimation of the AOD.

• However data on the precision of those AOD measurements is rarely provided.

• We have evaluated the effects of the inclusion of those exercise intensities on the AOD precision.

• The results have indicated that the inclusion of exercise intensities above the lactate threshold in the VO/running speed regression does not improve the precision of AOD estimation in endurance-trained runners.

• However, the use of sub threshold regressions may induce an underestimation of AOD comparatively to the use of complete regressions.