The Importance of the Leg Curl for Knee Health, by Matthew Romans
Posted March 20, 2020 by Matthew Romans
The knee joint is an essential joint for humans. When that joint is compromised, we cannot easily walk, run, climb stairs, stand, or support our own body weight. When most people think about strengthening the knee joint, they tend to think about the quadriceps muscles, which primarily function to extend (straighten) the knee. Often an afterthought are the hamstring muscles, which work to flex (bend) the knee. Many trainers and physical therapists tend to focus almost exclusively on performing leg extension exercises to strengthen the muscles surrounding the knee, but they very rarely incorporate the leg curl exercise for the hamstrings. This could be for two reasons. The most common reason is that they do not have access to a properly designed machine in their studio or clinic. The other reason is that they believe this exercise is contraindicated for their patients or clients; in my experience, this is very rarely the case.
To get a better understanding of the knee joint, we need to discuss its anatomy. The knee is a hinge joint that involves three bones: the femur (upper leg), tibia (lower leg), and patella (knee cap). There are four ligaments that connect the upper and lower leg bones, as well as tendons that connect the bones to the muscles that extend and flex the knee. In between the bones are pieces of cartilage which act as cushions. There are also bursa sacs located in the joint which secrete synovial fluid that helps to lubricate the joint (much like motor oil in your car's engine). While the knee is a fairly mobile joint, it can be susceptible to injury, either due to overuse or one traumatic event. A tear of the anterior cruciate ligament (ACL) is a single event injury that is very common in sports, while a gradual wearing of cartilage due to being a distance runner would be considered an overuse injury. The overuse injury could likely have been prevented (by not pounding your feet on the pavement day after day), while the ACL tear can often come down simply to bad luck. Sports injuries can never be completely prevented, due to the high force nature of sports and improper training techniques. One thing is certain: in order to strengthen the knee joint and reduce your risk for injury it is critical to strengthen all the muscles that surround the knee joint.
We talked earlier about the opposing muscle groups that surround the knee joint: the quadriceps and the hamstrings. As you probably guessed, there are four muscles that make up the quadriceps (vastus medialis, vastus lateralis, vastus intermedius, and rectus femoris). Conversely, there are only three muscles in the hamstring group (semitendinosus, semimembranosus, and biceps femoris), which means there is a natural imbalance between the two muscle groups. While it's important to perform regular knee extension exercises like the Leg Press for the knee, it's also important to balance that out with regular knee flexion exercises as well. This is why the Leg Curl exercise is so critically important.
In my opinion, no other exercise can engage the hamstrings as effectively as the Leg Curl. While the hamstrings are involved in the Leg Press exercise from a standpoint of hip extension, their involvement is sigificantly less than that of the glutes and quadriceps. In the Leg Curl, the hamstrings are the primary mover, with some assistance provided by the muscles of the calf (the gastrocnemius and soleus). Unfortunately, most Leg Curl machines are poorly designed, whether they are performed in a prone (when the client lies face down) or seated position. Most prone Leg Curl machines do not have a properly engineered cam to adequately vary the resistance. This results in the knees sliding forward and out of proper alignment with the axis of rotation, and it can also cause irritation to the lower back. Most seated Leg Curl machines in traditional gyms also do not have a properly designed cam, and have neither proper seat belts nor a coupled movement arm to prevent sliding forward of the knee joints or the pelvis during the exercise.
The Leg Curl machines at Total Results are engineered based on our exercise protocol's slow speed of movement, and they have a seat belt to properly restrain the pelvis and a coupled movement arm to keep the knees in proper alignment with the axis of rotation. Our machines are also designed with a floating seat to minimize knee irritation. There is a slight incongruity between the ovoid knee joint and the circular arc in which the movement arm travels. The floating seat helps to bridge that gap (so to speak) so that the client may move in a safe and pain-free range of motion.
The Leg Curl can be a challenging exercise to perform. Unlike the Chest Press, which most people can relate to from having done some variety of a push-up, the Leg Curl can seem like a slightly unnatural movement, since it isn't something most of us do in everyday life. It is also a blind movement, meaning that everything develops behind you during the positive phase of the movement. However, just because it creates some challenges doesn't mean that it shouldn't be performed in your exercise routine. We often have clients perform this exercise at the very beginning of a workout, just prior to the Leg Press. Performing a knee flexion exercise (Leg Curl) prior to a knee extension exercise (Leg Press) serves to properly warm up the knee joint and release synovial fluid, which helps to lubricate the knee. This will allow you to work intensely and further reduce your risk for injury, particularly if you already have knee issues. We can also modify how we perform the Leg Curl exercise if a client experiences pain during a dynamic movement. We can adjust the range of motion, perform a Timed Static Contraction, or even use negative-only protocol to strengthen the hamstrings without inflaming the joint.
Remember, the best way to strengthen your joints and be more resistant to injury is to strengthen the muscles surrounding the joints. Increased strength leads to improved function and a decrease in pain. The Leg Curl exercise is a vital one for overall knee health. The combination of Total Results exercise protocol, equipment, and instructors will safely maximize your benefits in minimum time. Experience the difference today.