Underestimation of Economy from Incremental Tests: Implications for Practitioners

Purpose: Current practices for estimating exercise economy using an extrapolation of sub-gas exchange threshold (GET), and to a lesser degree supra-GET, data will likely result an underestimation of actual economy, however, this is yet to be empirically demonstrated. Despite contentions, these protocols remain in widespread use. Therefore, the aim of the present study was to investigate whether estimation of exercise economy from moderate only, and moderate and heavy intensity exercise underestimates actual oxygen cost. Summary of Facts and Results: Twelve recreationally active males (mean ± SD; age 29 ± 9y, height 1.81 ± 0.07 m, mass 81.4 ± 10 kg) volunteered for this study. Following a maximal ramp test to determine the V̇O2peak, peak power (Wpeak), V̇O2 and power output at GET, participants completed a sub-GET only, a sub/supra-GET (both five-stage incremental tests), and a fixed WR protocol (10 min duration at 75% Δ). Economy was determined by extrapolation of sub- and sub/supra-GET V̇O2 and directly measured V̇O2 at 75% Δ. Within-subjects ANOVA was performed to identify differences in economy between sub-GET only, sub/supra-GET, and fixed WR protocols. Significant effects between the predicted values compared to the measured value were investigated post hoc using Bonferroni corrected paired t-tests. There was a significant effect of protocol on V̇O2 and economy (P <0.001, η2p = 0.645), where both methods of estimation underestimated the actual oxygen cost. In addition, estimation-using sub-GET data was significantly lower than sub/supra-GET (P <0.05). Conclusion: The large error obtained by extrapolating sub-GET exercise intensities for the purpose of estimating exercise economy needs to be acknowledged, as does the concomitant, albeit reduced, error that remains when incorporating supra-GET data. Exercise scientists and practitioners should adopt more appropriate testing protocols such as serial assessments, up-to and including race pace, to accurately assess economy.