TJ’s Drill – Dangers of Knee Extensions Posted on August 18, 2014 at 9:00 am. There’s a lot of different ways to strengthen your quadriceps. But there’s one thing you should avoid. St. Cloud Orthopedic Sports Medicine Director Tom Jensen explains what that exercise is and why you should never do it. Post navigation Expo for SeniorsPhysician Focus: Chad Holien, M.D.