In Chapter 2 the effects of growth, development and maturation on biological characteristics of young soccer players were considered. It was clear that during growth and development, soccer performance improved as players grew stronger, faster and had more endurance. Furthermore, their skills and game understanding became more sophisticated. Nevertheless, scientists are unsure of the precise effects that growth and development have on performance and whether it is influenced by sustained periods of sport-specific training. Intuitively, a combination of growth and training would be expected to optimise performance but there are limited data on this aspect of youth soccer.