So add triceps-to-elbows. There are a plenty of scientific studies on what causes injury in the gym. But lets get real the main reason for injury comes from lack of mind muscle connection, to much weight/bad form, and straining the joint while lifting ( behind the head military press would be a much better example then leg extensions if the article is going to say its SUCKS and you should NOT do it.) ( NEVER DO )..more interesting to me would be to see leg extensions left out if professional bodybuilding routines to see the form/shape of the whole leg. I do not disagree that it will cause stress, but I wouldn’t go as far as to slander. At some point you have to build the muscles around the joints to strenghten joint "To get unnatural results, we need to do unnatural things”. Yes squatting is a natural movement however its horrendous on the knees if your trying to do anything worth a damn at the gym! Perhaps I think it would be more suiting if the title was “If your injured or have joint issues, don’t do these exercises” IF its going to add in leg extension.