Do the speeds defined by the American College of Sports Medicine metabolic equation for running produce target energy expenditures during isocaloric exercise bouts?

The accuracy of the American College of Sports Medicine (ACSM) equations for producing predicted values of heart rate reserve (HRR) and oxygen uptake reserve \( (\dot{V}{\text{O}}_{2} {\text{R}}), \) and consequently, target energy expenditure (EE) during exercise are yet to be established. This study investigated whether speeds defined by the ACSM metabolic equation for running correctly estimate the EEs during isocaloric exercise bouts. Twenty-eight men performed a ramp-incremental maximal exercise test to determine HR_max and \( \dot{V}{\text{O}}_{2\max } . \) Two continuous exercise bouts at 60 and 80% \( \dot{V}{\text{O}}_{2} {\text{R}} \) and target EE of 400 kcal were then performed. In the 60% \( \dot{V}{\text{O}}_{2} {\text{R}} \) exercise the observed \( \dot{V}{\text{O}}_{2} \) and EE were lower than predicted only during the first time quartile of the bout (t = 6.5, p < 0.001), whereas at 80% \( \dot{V}{\text{O}}_{2} {\text{R}} \) it was lower during the first (t = 15.3, p < 0.001), second (t = 5.4, p < 0.001) and third (t = 3.1, p = 0.025) quartiles. The observed HR was lower than predicted in the first time quartile of the 60% \( \dot{V}{\text{O}}_{2} {\text{R}} \) (t = 5.6, p < 0.001) and 80% \( \dot{V}{\text{O}}_{2} {\text{R}} \) bouts (t = 10.7, p < 0.001), whereas no significant differences occurred for any other time quartiles (p ≥ 0.23). In conclusion, the running speed defined by the ACSM metabolic equation overestimated \( \dot{V}{\text{O}}_{2} \) and EE within exercise performed at 60 and 80% \( \dot{V}{\text{O}}_{2} {\text{R,}} \) especially in higher intensities.