rectus femoris

The rectus femoris (green marker) is one of the quadriceps muscles, but it is anatomically and functionally unique to the rest of the muscle group. The other quads simply cross the knee and attach to the femur. They are strictly knee extensors. The RF is biarticulate. It does not attach to the femur but crosses the hip joint and attaches to the pelvis, making it a hip flexor as well as a knee extensor. As a hip flexor, it plays a significant role in the swing phase of various forms of locomotion.

If you have ever had quad tendon pain above your knee cap, it is likely connected to tightness and/or weakness in the RF. If you have ever pulled your quad, the RF is the specific muscle that you injured. How do we prevent these injuries? The RF must be strong and flexible. For flexibility, see the video below. As for strength, how do we get strong quads? Just squat, right? Not in this specific case. To make a muscle strong, we need to put high load on it in a lengthened position. Because the RF crosses the hip, the hip flexion that occurs in the squat position means the muscle is shortened. This is shown in the picture above. Muscles do not produce a lot of tension in a shortened position, so squatting does not provide the same structural stimulus on the RF that it does on the rest of the quad muscles. Squats, pistol squats, step ups, lunges (front leg), these are all exercises that we use to strengthen the quads, but they actually neglect the RF.

The RF is lengthened when the hip is extended and the knee is flexed. This occurs under load on the back leg of a lunge. People typically think of lunges as being focused on the front leg. The demand on the glutes and the vastus muscles (the other 3 quads) is certainly the highest on the front leg, but the RF gets the best stimulus on the back leg. Of course the specific execution of the lunge is important. Here’s a few tips for strengthening the RF.
1. Keep weight on your back leg and push your back foot into the ground.
2. Lower into the lunge under control and stop the descent yourself. This portion of the movement is where you get the most muscle tension. You can touch your back knee to the ground but don’t just fall and rest on your knee.
3. Keep your torso upright to avoid hip flexion and shortening of the RF.

It is easy to neglect the rectus femoris in your strength training. Do an exercise for the RF regularly to make sure you don’t fall into that trap. There are other options, but lunges are a simple solution. Lunges don’t have to be heavy. They don’t have to be done multiple times per week. But don’t go months on end without doing them, so you don’t neglect a very important muscle.

Note: the rear foot elevated split squat lengthens the RF even more than a lunge. But it tends to take load off the back leg, and it may even stretch out the RF too much for a strength exercise. If executed correctly, it is certainly an option as well, but I prefer the simpler solution, which is lunges.

So having a flexible and strong rectus femoris should prevent pain above the knee cap as well as quad pulls. Lunges may be the long term key to eliminating these problems, because they strengthen the RF. But it’s important to understand that the strengthening is a response to a high amount of stress. With healthy tissue, stress is good. But when the tissue is unhealthy, the stress of lunges very well may be too much. It may make the problem worse. For those who currently have some pain, we have to find the correct amount of stress to progress the tissue toward being healthy again. For that purpose, use the rehab exercise in the second video below.