Whole-body volume of oxygen consumption while walking: Agreement between measured and estimated values

Predictive equations are widely employed for estimating the volume of oxygen consumption (VO2) while walking, which is ultimately employed to determine energy expenditure and tailor exercise prescription. This study aimed to test the agreement between the measured VO2 and estimated VO2 during a walking protocol on a treadmill at 3.5, 4.5, 5.5, and 6.5 km/h. Thirty-eight young adults (50% women) participated in this cross-sectional study. The Omnical (Maastricht Instruments, Maastricht, The Netherlands) and K5 (Cosmed, Rome, Italy) metabolic systems were used to measure VO2. To determine the predictive equations, a comprehensive literature search was conducted using the MEDLINE database from May 2022 to July 2023. Seven predictive equations were found and included for estimating VO2 values. We calculated the mean bias (mean difference between measured VO2 and estimated VO2) obtained at each speed using one-sample t-tests. We compared the VO2 measured and estimated values using repeated measures analysis of variance and the Bland-Altman method. One-sample t-tests showed that all score errors were different from zero (ranging from 1.1 to 5.4 mL/kg/min). Thus, no predictive equation estimated similar VO2 values in comparison with the Omnical and K5 metabolic systems at all intensities. However, the Weyand equation showed the lowest bias across all intensities (score error of 1.1 mL/kg/min). This study showed a lack of agreement between the Omnical and K5 systems compared to diverse predictive equations specially designed to estimate VO2 during walking. Nevertheless, based on our results, the Weyand equation should be the preferred option. The estimated VO2 values derived from all predictive equations showed no agreement with VO2 values measured by the Omnical and K5 metabolic systems, highlighting the importance of taking into account the error introduced by VO2 walking predictive equations when estimating VO2. The Weyand equation presented the lowest bias in comparison to the VO2 measured by the Omnical metabolic cart, which is the gold-standard metabolic cart (i.e., system of reference). These findings may hold practical implications when transitioning from clinically based programs to exercise interventions tailoring or self-guided exercise programs in young adults. Moreover, these results can contribute to individualize exercise programs by sport scientists using freely available and affordable tools as predictive equations.