Quads: What are they and what do they do?

Quadriceps are the largest group of muscles in the body.  The group is composed of; you guessed it, four muscles. These include the rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius. The rectus femoris is located in the middle of the thigh and is the most superficial muscle of the quad. The others are located deeper within the leg. The vastus lateralis is located on the lateral side of the leg (outside of the thigh). The vastus medialis is located on the medial side of the leg (inside of the thigh). Finally, the vastus intermedius is between the prior two muscles. The rectus femoris covers this muscle and cannot be seen unless you get cut open. All of these muscles are connected to our tibial tuberosity (the little bump below our knee cap). There is a fifth muscle of the quad called the articularis genus. It often isn’t included in the grouping as it is a small muscle and unique as it lies on the surface of the femur. For our purposes, we won’t go into too much detail on this muscle. To further complicate things, a sixth muscle has been discovered in recent studies. The tensor vastus intermedius runs between the vastus lateralis and intermdius. At one point it was considered part of the vastus lateralis. However, the actual muscle can be separated and has its own independent nerve supply that branches off from the femoral nerve. The presence of the muscle is variable however, and has not been seen in every subject. Because of this we will be excluding this muscle. Further research has to be done.

The function of the muscles in the quad group are all very similar. All four are responsible for extension at the knee joint. In simple terms, it causes your lower leg to move forward as if you were kicking a ball. Since the rectus femoris originates from the ilium (the top of the hip bone) it is a flexor of the hip. Again, simply put, this causes the knee to come up closer to the chest. Muscles, on top of allowing movement to occur, often have other functions. We often say deep muscles act as stabilizer muscles. Well the three deeper muscles of the quads, especially the vastus medialis, help to stabilize the knee joint and the patella.

Training the quadriceps is a relatively simple thing to do as they are involved in a lot of our daily lives. Exercises such as squats and lunges work the quads as well as other muscle groups. Isolation exercises like a leg extension will work the quads directly. As any kind of exercise program, a combination of isolation and compound movements will yield the best results.

As far as injuries go, the quads are not bulletproof. Being relatively larger muscles, injuries are not as debilitating as a rotator cuff for example. Muscle tears, strains, and contusions can happen. Rest, ice, compression, and elevation will be effective in these injuries. One of the more harmful injuries that can occur to the quads is tearing the quad tendon. Depending on the severity of the tear, surgery might be necessary. 

In conclusion, the quads are comprised of four muscles (sometimes 6). They are responsible for extension of the lower leg, flexion of the hip, and stabilization of the knee. Hopefully now that we have this knowledge, we can train smarter and keep our joints healthy.

Sean Willitts is an ACE certified personal trainer. He graduated from Kutztown University in 2015 with a bachelor’s is sport management and a minor in fitness. Including training at Body Elite, he is also a record holding powerlifter. He uses his practical experience and knowledge to help his clients achieve their strength and fitness goals.