497 Pediatric Exercise Science, 2010, 22, 497-510 © 2010 Human Kinetics, Inc. ORIGINAL RESEARCH Mendez-Villanueva, Buchheit, Kuitunen, Poon, Simpson, and Peltola are with the Sport Science Dept., ASPIRE, Academy for Sports Excellence, Doha, Qatar. Is the Relationship Between Sprinting and Maximal Aerobic Speeds in Young Soccer Players Affected by Maturation? Alberto Mendez-Villanueva, Martin Buchheit, Sami Kuitunen, Tsz Kit Poon, Ben Simpson, and Esa Peltola ASPIRE, Academy for Sports Excellence The purpose of this study was to investigate the relationship between maximal sprinting (MSS) and aerobic (MAS) speeds in a cohort of highly-trained young male soccer players with the infuence of body mass controlled for using allome- tric scaling. MSS and MAS were obtained in 14 pre-age at peak height velocity (APHV) players (12.3 ± 0.7 years), 21 circum-APHV players (14.3 ± 0.9 year) and 26 post-APHV players (16.9 ± 0.7 years). The three groups showed similar positive correlations between MSS and MAS (r = 0.73 to 0.52; p < .01). In con- clusion, our results suggest that the relationship between MSS and MAS is not affected by maturation. Morphological and physiological considerations suggest that sprinting ability and aerobic function (e.g., aerobic power and endurance capacity) put conficting demands on the design of a human’s locomotor apparatus and therefore cannot be maximized simultaneously (31). The intuitive basis of this performance trade-off probably stems from the observation that elite specialist sprinters and marathon runners differ substantially in size and shape, and no athlete excels in both events. In addition to cardiorespiratory attributes, individual differences in the proportion of fast, powerful muscle fbers to slow more fatigue-resistant fbers are believed to be the primary physiological basis of this performance trade-off (34). Consistent with this suggestion, short-distance human sprinters possess a greater proportion of fast-twitch muscle fbers than do endurance athletes, and vice versa for the slower more fatigue-resistant muscle fbers (7,12). A genetic-based trade-off between sprint and endurance phenotypic traits has been suggested such as that an individual is inherently predisposed toward performance in either sprint/power or endurance events (19,35). However, team sports such as soccer require a more complex (mixed) phenotypic trait, as both qualities (i.e., speed and aerobic function) infuence high-level soccer performance (22,28). Thus, successful young soccer players are expected to be selected and systematically trained to develop both qualities (i.e., speed and aerobic ftness; 23). Accordingly, the presence of functional trade-offs