Casado, A, Hanley, B, Santos-Concejero, J, and Ruiz-Pérez, LM. World-class long-distance running performances are best predicted by volume of easy runs and deliberate practice of short-interval and tempo runs. J Strength Cond Res XX(X): 000-000, 2019-The aim of this novel study was to analyze the effect of deliberate practice (DP) and easy continuous runs completed by elite-standard and world-class long-distance runners on competitive performances during the first 7 years of their sport careers. Eighty-five male runners reported their best times in different running events and the amounts of different DP activities (tempo runs and short- and long-interval sessions) and 1 non-DP activity (easy runs) after 3, 5, and 7 years of systematic training. Pearson's correlations were calculated between performances (calculated using the International Association of Athletics Federations' scoring tables) and the distances run for the different activities (and overall total). Simple and multiple linear regression analysis calculated how well these activities predicted performance. Pearson's correlations showed consistently large effects on performance of total distance (r ≥ 0.75, p < 0.001), easy runs (r ≥ 0.68, p < 0.001), tempo runs (r ≥ 0.50, p < 0.001), and short-interval training (r ≥ 0.53, p < 0.001). Long-interval training was not strongly correlated (r ≥ 0.22). Total distance accounted for significant variance in performance (R ≥ 0.57, p < 0.001). Of the training modes, hierarchical regression analysis showed that easy runs and tempo runs were the activities that accounted for significant variance in performance (p < 0.01). Although DP activities, particularly tempo runs and short-interval training, are important for improving performance, coaches should note that the non-DP activity of easy running was crucial in better performances, partly because of its contribution to total distance run.