Objectives. Our aims were to determine whether there is any significant diffe- rence between the measured and estimated energy expenditure for the most commonly used prediction equations in the literature, and to develop a new specific prediction equation for aerobic interval training with a broader cross- section of the population in terms of age, fitness and body mass index (BMI). Methods. Twenty healthy participants were recruited for this study. Two groups of ten people were established depending on their BMI. The low BMI group ranged between 19 and 22, and the high BMI group between 26 and 29. The test protocol consisted of 12 individualized intensities, 6 walking and 6 run- ning speeds on a treadmill, measuring both heart rate and energy expendi- ture. The rest time between intervals ranged between 1 and 2 minutes Main results. The measured oxygen consumption was found to be signi- ficantly different from those predicted by the walking and running equa- tions selected from the literature. The Léger equation was the best of the tes- ted equations to estimate oxygen consumption for walking and the ACSM formula was the best for running. However, neither was found to be very accurate. Conclusions. The prediction equations selected from the literature in this study were not accurate enough to estimate oxygen consumption during aerobic interval training. We propose four new formulas to improve the estimation of the metabolic cost in interval activities in a population with wider characteristics than those found in the literature.