One month after a knee replacement, the thigh muscle has lost about 60% of its strength. Most of that loss isn't from the scalpel. It's the nervous system switching the muscle off to protect the joint.You can't stop that switch from flipping. You can decide how strong the muscle is when it does.
That is prehab. Training for surgery the way an athlete trains for a match.
Then, do your prep
Your surgeon prepares for the operation. Your body should prepare too.
Prehab means strengthening and activating the muscles that will be affected by surgery, before the surgery. It also means rehearsing the exact exercises you'll do afterwards, while you're pain-free and can learn them properly.
The evidence is now strong. A 2026 meta-analysis in the Journal of the American College of Surgeons pooled 23 randomised trials with over 2,000 patients. Exercise or nutrition-based prehab cut the odds of post-operative complications roughly in half and shortened hospital stays.
The size of the benefit depends on the surgery. It is largest in major operations such as lung and abdominal surgery, and in procedures where strength decides the outcome, such as ACL reconstruction.For ACL patients, the long-term data is especially clear. In the Delaware-Oslo cohort,
72% of patients who completed extended prehab were back to their pre-injury sport at two years, compared with 63% who weren't.
Prehab is also one building block of ERAS — Enhanced Recovery After Surgery — the multidisciplinary pathway surgeons use to reduce surgical stress and speed recovery.
When should you start?
Ideally 2–6 weeks before surgery, depending on how much time you have between diagnosis and the operation date.
Short on time? Start anyway. Even one or two sessions set a strength baseline and teach you your first post-op exercises. Day one after surgery is a terrible day to learn something new.