Leg extension also maximize shearing force on knee and patella. The aggressive extension of his lead leg builds force under his foot, causing it to pop up and move away from the ball (the opposite direction that he was pushing). Unlike squats and lunges, which load the knee primarily with compressive (downward) force, quad extensions apply shear (front-to-back) force. Post by jwcalla » Fri Mar 09, 2007 5:10 pm Thanks guys for all the info. If leg extensions are bad because of shear forces at the knee joint, what about skullcrushers and cable pushdowns? That exercise, because if it's very nature (Open-kinetic-chain), puts excessive shear force on the knees. Furthermore, because the angle of the leg was measured throughout the movement, it allowed the researchers to study the shearing forces of the limbs. And fear not, I wouldn't dare replace squats with leg extensions. Thus, by starting from about a 90 range of motion, decreases the shear force on the knees. No matter the state of your knees, safely and effectively performing leg extensions relies on good form. And just as recently on my 45 degree leg press ive been developing pain in my patella. University of South Wales. 9. The leg extension is a popular way to train the quadriceps at the front of your knee. ... Biggest thing for shear force on the knee is the knee doing past the toes, teaches it bad neuromuscular firing patterns and increases likely hood of an ACL tear. This is because the movement places a lot of shear force on to the back of the patella (your knee cap), which forces the tibia (the bone in your lower leg) towards the femur (your thighbone). Knee extension acts as an unloaded function of the quads. George Zafiropoulos. Now look at Walker. This can lead to cartilage damage. Kenny Croxdale. The leg extension is a popular way to train the quadriceps at the front of your knee. I recently started being very consious not to let my knee go past my toes after watching scott herman on youtube profess this point. Years ago when I was in school to become an engineer, I wrote a paper on this very subject, and how over time heavy shear force will open up the knee joint up. Leg extensions are infamous for being bad for your knees. It's appreciated. When you squat, the thickest part of the cartilage is loaded during the squat's maximum force. Never before has this happened. The leg extension places maximum force on the back of the patella ("knee cap"), the thinnest portion of the cartilage. Shear force during leg extensions Thank you standapart for that link! But heavy weights and … It is not natural to load the knee while the foot travels through space with open-chain movement. this is how I feel as well, the problem is the knee joint is built for compressive force, and the leg extension places shear force on the knee. But heavy weights and improper form increase your risk of knee injury. Try to think of a normal free weight movement that would involve knee extension with resistance. Cite. The most shearing occured in the final third of a full range of motion during the concentric phase, at the very top of the leg extension. [/quote] Shear Force On The Knees The degree of shear force on the knee occurs primarily in the bottom part of the Leg Extension. Leg extensions place a lot of shear force on the knees. 14th Jun, 2018. High Repetition Loading Close. Unstable knees are more vulnerable to injury from shear stresses as opposed to compressive forces. Top. The leg extension prevents force from the back, destabilizing the knee. jwcalla Rookie Posts: 35 Joined: Wed Jul 19, 2006 11:01 pm.
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