Wednesday, August 5, 2009

Substitutes: Combating Fatigue or a Strategic Change?

On February 10, 2008, during a scoreless draw with Siena, AC Milan coach Carlo Ancelotti, subbed in Alberto Paloschi. Fifteen seconds later, on his first touch of the match, Paloschi scored the only goal of the match. Many times matches hinge of the strategic use of substitute players. Coaches typically make substitutions late in the match for two key reasons. The first is a tactical move, as with Paloschi, an effort to increase the chances to earn a goal or to hold onto a lead. The second is to replace a player who is showing signs of fatigue, one whose work rate has declined. A recent study looked at this latter reason. Do coaches substitute players for lack of effort and do these substitutes pay off with higher level of intensity?

Researchers examined teams from the French First Division professional league. They tracked individual player movements using a multiple-camera tracking system. Over the course of the season, they followed the movements of both starters and second-half substitutes. The work rates of substitutes were compared to those of players remaining on the field and to the work rates of the players that were replaced. The researchers quantified “work rate” based on the distance ran, the number of high intensity efforts (e.g. sprints) and the recovery time between sprints.

By measuring player work rate, the investigators came away with three key findings. First, there was no drop off in the work rate of players who were replaced. The players who were subbed out showed the same work rate in both the first and second periods with no signs of fatigue. This suggests that most of the substitutions were made for strategic reasons rather than to remove a player who was fatigued.

Second, the work rate of forward substitutes was no greater than the work rate of the players that they replaced. In fact, the replacements had a slightly lower work rate during their first 10 minutes of play. The researchers mention that this may be due to the substitutes not being able to “get into the game”. It is also possible that match conditions, such as trying to protect a lead, may limit a substitute forwards involvement.

Third, the midfield substitutes work rate was noticeably greater than that of the players that were replaced. They tended to cover more distance and a higher intensity and spend less time recovering between sprints. It seems that midfield replacements get involved in the match more quickly that forwards.

This preliminary study provides some insight into why substitutions are made and if this strategy can potentially affect the match. However, as with many research projects, it also raises a number of important questions. First, do work rates of substitutes vary based on the status of the match? Will a replacement forward work at a high rate if his/her team is trailing? Second, when protecting a lead, teams often replace a forward with a midfielder. Does this affect the work rate of either the substitutes or players remaining on the field? Lastly, these results suggest that forward replacements do not utilize their full physical potential compared to midfielders. Perhaps this information can be used to emphasize the need for forward substitutes to elevate their intensity during the initial minutes after they enter the match.

Reference:

Carling C, Espie V, LaGall F, Bloomfield J, Jullien H (2009) Work-rate of substitutes in elite soccer: A preliminary study. Journal of Science and Medicine in Sport, doi:10.1016/j.jsams.2009.02.012