The Leg Extension Returns
Closed-kinetic-chain exercises are physical exercises performed where the hand or the foot is fixed in space and cannot move. Open-kinetic-chain exercises are said to be performed whereby the hand or foot is free to move. The leg extension would be considered an open-chain movement and the barbell squat a closed-kinetic chain exercise.
In the early 1990's Lutz and his colleagues studied these two conditions examining shear forces during rehabilitation of the knee. They concluded that closed-kinetic-chain exercises produced significantly greater compression forces and increased muscular co-contraction at the same angles at which the open-kinetic-chain exercises produced max shear force and minimum muscular co-contraction. Co-contraction meant the quadriceps and hamstrings were working together during rehabilitation to protect the joint from shear.
Pendulum Leg Extension
The conclusion of the aforementioned study led doctors and athletic trainers to reevaluate their approach to the rehabilitation of knee injuries. Since shear forces are perpendicular to the direction of extension and rehab was occurring on repaired tissue, they gathered the leg extension was not a positive. Based on the findings they also assumed that leg extensions could be dangerous, especially since there was little co-contraction of the hamstring and quad to protect the knee as it was being re-strengthened. The medical staff went even further, the leg extension was deemed a bad exercise for many years even though it had been the staple of rehabilitative exercise.
In the 2000's Mikkelsen and colleagues dispelled the myth. They determined that by adding open- kinetic chain exercise to rehabilitation after ACL reconstruction resulted in a significantly better improvement in quadriceps torque without reducing knee joint stability. At 6 months those using open-chained exercise were returning to activity earlier and at the same level as before injury.
The leg extension was vindicated! Many studies since have substantiated that a leg extension is not only a great rehab tool, but that muscular strength of the knee extensors is related to the speed an athlete can produce during a single-sprint performance.
The leg extension is back and the quads are Getting Strong.