Monday, November 16, 2009

Trade-offs Between Speed, Shot Velocity and Accuracy

Successful goals typically come from shots that have both pace and accuracy. How players approach the ball when taking a shot can affect both of these parameters. Rushing a kick can result in a shot that is both slow and less accurate. Slowing the approach can improve accuracy but reduce shot velocity. To better understand these relationships, researchers at the University of Aarhus in Denmark looked at the trade-offs between approach speed, shot velocity and accuracy. They found that players generally self-select the optimal approach speed for both shot velocity and accuracy. The implications are that forcing players to alter their approach speed, defenders may be able to adversely affect the attacker’s shot and reduce the chances of conceding a goal.

The study enrolled a group of trained players from the Danish professional leagues (20-30 years of age). They were asked to take a series of shots on goal. The first set of shots was for speed. Players were told to take their normal approach and kick for maximal ball speed. They were then asked to repeat using various approach velocities ranging from standing still to 150% of their normal approach speed. The second set of shots was for accuracy. Here they were asked to hit a target positioned just above field level. The idea was to simulate a penalty kick placed in the side of the goal with enough pace to prevent a goal keeper from blocking the shot.

For all of the shots, both the player’s approach velocity and shot speed were recorded.

All of the players self-selected an approach speed that maximized their shot velocity. That is, when they approached the ball faster or slower than normal, their shot velocity decreased. This approach speed was between 52-77% of their peak running velocity. When players increased their approach speed by 50%, their shot velocity fell by as much as one-third. Slower approach speeds also slowed shot velocity by up to one-quarter.

One of the more interesting findings was that approaching the ball at near maximal running speed resulted in shots that were actually slower than those taken without an approach (standing still).

When a target was used and accuracy was required, peak shot velocity dropped by ~15%.

The results indicated a couple of things. First, players generally self-select the approach velocity that gives them the greatest shot speed. Increasing or decreasing the approach run results in slower shots.

How does this study fit into game situations? Here the authors raise an interesting scenario. They point out that there are situations where a defender is chasing an attacking player who posses the ball. The defender has to make a decision – make a take and risk not winning the ball or continue running with the attacker and risk giving up a shot. They suggest that the better option is to force the attacker to run at a high speed, increasing his or her approach speed when the shot is taken. This should then result in a shot that has a lower velocity and less accuracy.

This study may also have implications for training attackers. Often players train by taking shots at a self-selected approach speed, one that maximizes shot velocity. During game situations, slower and less accurate shots probably result from approaches that are outside of the players “comfort zone” for approaching the ball. Perhaps it is possible that training with varying approach speeds might expand this comfort zone. Players may then be able to better maintain near maximal shot velocities during match situations. An interesting concept, but one that needs a bit more research…

Reference:

Andersen TB, Dorge HC, (2009) The influence of speed of approach and accuracy constraint on the maximal speed of the ball in soccer kicking. Scandinavian Journal of Medicine and Science in Sports. DOI: 10.1111/j.1600-0838.2009.01024.x