Accuracy of Metabolic Prediction Equations for Obese Adults Walking at Various Speed and Grade Combinations

Abstract

Obesity is due to an imbalance of energy intake and expenditure, and both diet and physical activity are essential tools in weight management. Accurate estimates of physical activity energy expenditure are essential if obese individuals are to successfully manage their weight. Equations that predict metabolic rate during walking are used to determine energy expenditure but it is not known if these equations are accurate for obese individuals, particularly when walking uphill. PURPOSE: To compare the ACSM and Pandolf metabolic prediction equations to measured oxygen consumption and metabolic rate values in obese individuals walking across a range of speeds and grades. METHODS: Twenty six obese adult volunteers, mass = 102.3(15.8) kg, BMI = 35.0(4.5) kg/m2, (mean (SD)), participated in this study. We measured oxygen consumption while subjects walked on a dual-belt force measuring treadmill at ten different speed/grade combinations ranging from 0.50 m/s to 1.75 m/s and 0° to 9°. RESULTS: As expected, oxygen consumption and metabolic power increased with walking speed and grade, ranging from 11.4(0.3) mlO2/kg/min (399(15.8) W) at 1.25 m/s, 0° to 19.5(0.3) mlO2/kg/min (683(21.9) W) at 1.50 m/s, 3°, (mean (SE)). During level walking, the ACSM equation underestimated oxygen consumption, particularly at the fastest walking speed (22% at 1.75 m/s, 14.0 vs. 17.8 (0.4) mlO2/kg/min, p<0.001). The Pandolf equation accurately predicted level walking metabolic power. During uphill walking, the ACSM prediction equation consistently overestimated oxygen consumption by 5-13%. The Pandolf equation overestimated metabolic power by 0.6-12% in all but the slowest speed, steepest grade condition (0.5 m/s, 9°), during which metabolic power was underestimated by 4.9% (464(14.4) vs. 489(14.9)W). CONCLUSION: The ACSM prediction equation may not accurately estimate oxygen consumption in obese adults during uphill or fast, level walking and could result in a significant overestimate of energy expenditure during uphill walking. These results suggest the need to develop a revised ACSM equation for the obese population in order to ensure weight management success. Alternatively, one could consider using the Pandolf equation to estimate metabolic rate and energy expenditure in obese adults. Supported by NIH Grant R03AR059264