Recent reviews of how training affects running performance have indicated, to varying degrees, that running economy (RE) is a determinant of running performance. However, the literature suggests that the relationship between training-induced changes in biomechanics and RE is still largely unknown. While there is some evidence that high intensity interval training, plyometrics, and altitude/hypoxia training can improve economy, it remains unclear how these improvements are mediated. In addition, although it is clear from the literature that meaningful differences in RE exist among runners, the causes for the inherent differences are not clear. Consequently, suggestions are made to explore more individualized and integrated models of the determinants of performance that might better explain the interrelatedness of gait, RE, V˙O2max, and peak performance.