This exercise is another pet peeve of ours, and it’s all too common in gyms. People see ‘insert famous body builder here’ doing this exercise, and therefore think it must be good.
Here’s why it is bad:
1) It puts a lot of unnecessary stress on the patellofemoral joint
2) It preferentially recruits rectus femoris before the vastii muscles of the quad (it recruits VMO last, which is arguably the most important knee stabiliser!)
3) It increases lateral patellar deviation
4) It puts the ACL (ligament) under constant tension
5) It has reduced hamstring and gluteus activity
6) It has poor functional application for most athletes (the only thing it might help with is kicking a ball harder, but even then there are much better ways of training this pattern)
What does this all mean:
Leg extensions train your knee into some horrible movement patterns. All of these problems are things us physiotherapists are constantly trying to reverse. So please, take knee extensions out of your program ASAP. Literally almost any other leg exercise is better! (Side note: there are some rare circumstances where it can be beneficial, eg. when rehabbing a patellar tendinopathy, but for 99% of you this isn’t relevant)
Our caring and friendly Chatswood or North Sydney Physio team would love to help you out, so reach out to us if you have any questions.