Many athletes suffer knee injuries that damage the anterior cruciate ligament (ACL). The injury may weaken the ligament or tear it completely. In the case of an athlete with a tear, surgery is usually done. When the ligament is damaged but not torn a rehabilitation program may be advised.
Bracing is an important part of rehab for the ACL. A knee brace can protect the joint during some activities such as walking. It does not offer the same protection during sports activities. A brace can improve jumping, but does not increase running speed.
A knee brace can also improve how fast the hamstring muscle behind the knee reacts to movement. This muscle keeps the lower leg bone (called the tibia) from moving too far forward when the knee is straightened. In this way, the hamstring muscle protects the ACL by its quick reflex action.
When the muscles around the knee are fatigued from use, the hamstring reaction time is slowed down. This is true even with the brace on. Importantly, athletes should not rely on bracing to protect their knee during exercises or activities that fatigue the hamstring muscles.