This evidence seems to be especially important for the N-Exp group. The non-experienced participants demonstrated a poorer adaptation to 6 vs. 6 + GKs, explained by differences recorded in the results of offensive sequences and especially by the greater number of unsuccessful offensive sequences in this game format. Our data suggested that the game AZD9291? format clearly affects the quantity and quality of performed actions and, consequently, the offensive sequences�� characteristics. Katis and Kellis (2009) argued also that SSGs can serve several purposes as specific means of training. According to Reilly (2005), since young players need to develop physical abilities, technical skills and decision making in specific performance contexts, it makes sense to use SSGs depending on the age of the participants.

However, youth soccer coaches should be aware that age is not a very precise variable to use in the organization of the training task. Even within the same age group, it is possible to note considerable differences in individual and collective performance of players with well distinct skill and experience levels. In summary, the present paper has evidenced that the deliberate practice experience (individual constraint) and the SSG format (task constraint) do not depend of each other (interaction effect) to influence the offensive performance of young soccer players. Both factors affected independently the characteristics of the offensive sequences. Findings confirm that SSGs can serve several purposes as specific means of training.

However, for effective skill acquisition and performance enhancing in youth soccer, the manipulation of pitch size and number of players should always consider the players�� individual constraints. In this sense, smaller game formats seems to be particularly suitable for novice athletes (e.g., children/youngsters without experience and/or with a lower skill level), since they constrain the development of sport-specific skills based on a major involvement with the ball. On the other hand, in larger SSG formats, the number of actions that each player performs on the ball tends to decrease, increasing the number of ��off-the-ball�� movements and the need to form an effective unit of cooperation with teammates. Such game formats may be useful to practice the specific movement requirements of competitive situations (Hill-Haas et al.

, 2009), and should be carefully considered as young players improve game understanding and specific motor skills. Further studies should continue to verify how the GSK-3 task constraints imply the efficacy of the learning process in soccer, aggregating different contexts and players�� experiences. The functional impact, as far as technical and tactical behavioral changes in consequence of pitch size and number of players�� modifications are concerned, should be clarified. Acknowledgments The results of this paper were previously published in the Book of abstracts (pp.