Squats Are Better Than Leg Extension on the ACL

Most clients at fitness clubs and athletic performance centers prefer to perform the leg extension over squatting to help them develop the quadriceps muscles. They are both common exercises but leg extensions do have their drawbacks.

The ACL is the anterior cruciate ligament. It is one of four main ligaments that attach the tibia-fibula to the femur. The ACL is torn by tibia translation.

Squats are a closed kinetic chain exercise, which is defined as exercises where the foot is in direct contact with a solid surface, and are used by sports performance coaches for many reasons. They are a multiple joint exercise. The primary joints that a squat is involved with are hip, knee, and ankle. The gluteus maximus (butt muscles) is the main muscle used at the hip. The primary muscle used at the knee are the quadriceps muscles. The ankle’s primary muscle is the gastrocnemius (calf). Squats are a common way to measure for lower body strength and involve most muscles and joints in the leg.

Leg extensions are open kinetic chain exercises, which is defined as exercises where the foot is not in contact with a solid surface. They are also single joint exercises which means that only one joint and one muscle are working at a time. The leg extensions isolate the quadriceps, the primary movers. They allow the user to fix bilateral deficits, that may lead to injuries if not addressed. Leg extensions are easy to use machines that require little coaching or technique. When using leg extension, it may feel like it is a safe exercise, but not always for the ACL. There is a lot of tibia translation in the knee, and all of the force applied during a leg extension is on the knee. Hamstrings are not activated during a leg extension, which then the quadriceps are the only muscle that applies force on the ACL.

Leg extensions may look and feel safer but the risk of using one may be high. Squats are safer on the knee than leg extension, because the tibia does translate as much. Squats allow forces to be exerted into another object, unlike leg extension which exerts force on the joints. Research suggests that squats are safer than leg extensions.

References:

Horrigan, J. M. (n.d.). Leg Extensions vs. Squats. Retrieved June 26, 2016, from http://www.ironmanmagazine.com/leg-extensions-vs-squats/

Leg Extensions/Leg Curls Vs Squats. (n.d.). Retrieved June 26, 2016, from http://www.fitstep.com/Library/Questions/Questions/Exercisetech/leg-extensions-leg-curls-advantages-squats.htm