Most ACL injuries occur when the knee is perfectly straight or slightly bent. This type of injury can happen when a player is running, jumping, or standing still. In soccer, the ACL is most likely to be injured when a player is running and changing directions quickly, stopping suddenly, or twisting the body over the foot. Jumping and landing on the foot with the knee twisted can also cause problems.
New technology has allowed researchers to measure the strain placed on the ACL. One important discovery has been that stopping suddenly (rapid deceleration) puts a high level of strain on the ACL. This occurs when the foot makes contact with the ground and the leg is at its straightest. Doctors and physical therapists are working together to develop an exercise program that will prevent these types of injuries.