Energy Expenditure Equation Choice: Effects on Cycling Efficiency and Its Reliability

Purpose: There are several published equations to calculate energy expenditure (EE) from gas exchanges. We assessed whether using different EE equations would affect gross efficiency (GE) estimates and their reliability. Methods: Eleven male and three female cyclists (age: 33 ± 10 years; height: 178 ± 11 cm; body mass: 76.0 ± 15.1 kg; maximal oxygen uptake: 51.4 ± 5.1 ml·kg-1·min-1; peak power output: 4.69 ± 0.45 W·kg-1) completed five visits to the laboratory on separate occasions. In the first visit, participants completed a maximal ramp test to characterize their physiological profile. In visits two to five, participants performed four identical submaximal exercise trials to assess GE and its reliability. Each trial included three 7-min bouts at 60%, 70% and 80% of the gas exchange threshold. EE was calculated with four equations by Péronnet & Massicotte, Lusk, Brouwer and Garby & Astrup. Results: All four EE equations produced GE estimates that differed from each other (all P < 0.001). Reliability parameters were only affected when the typical error was expressed in absolute GE units, suggesting a negligible effect—related to the magnitude of GE produced by each EE equation. The mean coefficient of variation for GE across different exercise intensities and calculation methods was 4.2%. Conclusions: Although changing the EE equation does not affect GE reliability, exercise scientists and coaches should be aware that different EE equations produce different GE estimates. Researchers are advised to share their raw data to allow for GE recalculation, enabling comparison between previous and future studies