ACL reconstruction rehabilitation is a very long, drawn out process.  Because of the way the body heals from those particular ACL procedures, the recovery is broken into a series of parts. 

The first, is either non-weight-bearing, partial weight-bearing, or full weight-bearing, with some form of immobilizer or ACL extension brace. The second; gradually strengthening while recovering the range of motion inhibited by the brace and swelling. The third; progress to higher level activity, beginning with jogging, biking, and swimming. 

The final 4-6 weeks of a 6-month protocol for young, active individuals includes a series progressions that include jumping, hopping, sprinting, deceleration training, and lateral movements. During this time frame, these individuals face an unusually high risk for a hamstring strain on that same, affected leg. But why?

Hope Hillyard, our Head Physical Therapist, goes more into detail: 

"The hamstrings are synergist to the ACL. While the ACL is recovering from reconstruction, [and likely will not be at 100%], more stress can be placed on the hamstrings muscle group and therefore, subjecting the hamstrings to a higher risk of strain, or being overworked." 

So, let's break this down. The ACL and hamstrings work together to solidify the knee joint in terms of preventing the femur from moving forward. In other words, anterior, or forward movements are what the ACL specializes in. The hamstrings muscle group also acts as as a stabilizer at the front of the knee joint - and when the ACL is not healthy enough to primarily prevent injury, the hamstring must compensate. 

The reason this is more likely during that last stage of rehabilitation is because the body is finally ready to increase the stress on the ACL as opposed to strengthening the muscles around it, and therefore, putting it to the test. Activities such as sprinting, lateral movements, and deceleration training accentuate the ACL, and when the body is not used to that load, it will recruit the help of the hamstrings. The exertion of so much extra force is more than enough to strain a hamstring muscle.

"It also depends on the procedure the patient underwent," Hillyard mentions, "For example, if a patient and their orthopedic surgeon opt for a hamstring autograft, the hamstrings muscle group will likely be at higher risk for strains, as those muscles are healing, too." 

This doesn't mean it's not safe to push your body, at that point. It's a gradual process, and your physical therapist knows based on experience combined with objective measurements what the body can and cannot handle. This also doesn't mean that strains are expected during recovery - there is just an increased risk. You can help prevent hamstring strains by listening to your physical therapist when they tell you to hold off on a certain activity, and by taking it slowly when you're cleared to move to another level. Remember: the body has been unable to do higher level activity for months up to that point, and it's best to ease in. 

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