Delta economy of walking is not associated with body mass index in physically inactive adults

Abstract

PURPOSE: Published data on the relationship between body mass index (BMI; kg/m2) and energy cost of walking is inconsistent. The aim of this study was to determine whether the increased energy expenditure (EE) that occurs with increased walking speed (defined as delta economy) is associated with BMI. The primary hypothesis was that BMI does not influence delta economy. METHODS: Insufficiently active adults (total n = 187[GG1], males n = 87, females n = 100, BMI = 20.0-39.5 kg/m2,18-60 years) walked on the treadmill at 2, 3, and 4 miles per hour (mph) while ventilation and gas exchange were measured with an indirect calorimetry system (Jaeger Oxycon Mobile) for determination of oxygen consumption (VO2), carbon dioxide production (VCO2), and respiratory exchange ratio (RER). VO2 and RER were used to calculate EE (w/kg). Each subject walked for six minutes at each speed. Only the last three minutes of EE per stage were used after verification of steady state. Delta economy was captured by analyzing the slope of change of VO2 across walking speeds. Two methodologies were employed to quantify the slope: a novel technique using polynomial random coefficient regression (PRCR) and the traditional delta economy (TDE) method of calculating change in EE for a change in speed. Two key PRCR components were generated: linear and quadratic coefficients. TDE was determined for three speed changes: 2-3 mph, 3-4 mph, and 2-4 mph. The relationship with each of these to BMI was examined via Pearson product-moment correlation with α set at 0.05. RESULTS: BMI was not associated with either the linear ( r = 0.01, p = 0.87) or quadratic ( r = 0.08, p = 0.28) PRCR coefficients. There was no relationship between BMI and TDE at any of the speed intervals: 2-3 mph ( r = 0.07, p = 0.32), 3-4 mph ( r = 0.05, p = 0.53), or 2-4 mph ( r = 0.01, p = 0.87). CONCLUSION: In this sample of inactive adults, BMI did not influence traditional delta economy or the linear and quadratic coefficients from the PRCR model. Consequently, our results indicate that the considerable between-subject variability in all measures of walking economy is not affected by BMI. A strength of this study is the large sample size, which reduces the likelihood of sampling bias that might be present in previously published studies with much smaller sample sizes. This analysis was conducted on a baseline dataset collected as part of a project funded from a grant from the National Cancer Institute at the National Institutes of Health (R01CA198915). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.