One of the weaknesses of many physical therapy ACL reconstruction protocols is the blind eye that tends to be given to the opposite lower extremity. Researchers from South Korea present a nice study here reminding us not to ignore that OTHER lower extremity following ACL reconstruction.
The authors of the study found that while the strength EVENTUALLY comes back, the opposite/contralateral lower extremity does indeed get weaker and remains that way for up to 24 months. Two years. (Check out the graph below.) Most athletes return to sports before a year (6-9 months is typical). If that is the case (I tend to believe a longer time frame is indicated), they return with an ACL that has yet to fully heal and a contralateral lower extremity that has not regained its pre-injury strength. To me, that is a recipe for disaster.
At a minimum, we need to include the other side during the rehab process. I would go further by suggesting that we delay return to sport longer.