Di Salvo and Pigozzi (1998) evaluated the effectiveness of an eight month individualised training program for association football players based upon their position in the team. The reasoning behind such a program was the findings of previous research such as Ekblom (1986), that demonstrated a difference in the physiological requirements of players who played in different positions. Using a control group of same position players they demonstrated an improvement in a range of physical tests that was significantly better than the control group who continued to use the group training approach. However, because of the age of the subjects (17 years) it could be argued that the improvements were caused by maturation due to physical development. The external validity of this study is limited somewhat by the difficulties a coach would have in implementing such a program to a professional squad. It may be very impractical to implement and it may have a detrimental effect on team spirit if the players are not training as a group. For example, one player may think he is being asked to do more training than another and feel that this is an injustice.