How the Quadriceps Muscles Work

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The quadriceps muscles, commonly called the "quads," are powerful muscles involved in lower body movement and propulsion. The quadriceps muscles consist of four large muscles at the front of the thigh: the rectus femoris, vastus intermedius, vastus lateralis, and vastus medialis. These muscles are primarily responsible for hip flexion and extension at the knee joint.

Exercises that improve the quadriceps muscles are leg presses, squats, and leg extensions, among others. Keeping the quadriceps muscles healthy will help you to move through regular daily activities like climbing stairs and getting out of a chair with greater ease. It will also help to improve your performance in athletic activities like running, cycling, or team sports such as football or soccer.


Each muscle that makes up the quadriceps group has a different location and a different function. Each muscle has a different origin but they all attach near the patella (the kneecap). The femoral nerve innervates the quads and they get their blood supply through the lateral femoral circumflex artery.

Rectus Femoris

On many people, the rectus femoris is the most noticeable muscle in the quadriceps group as it runs down the middle of the front of the thigh. The rectus femoris has a fusiform (spindle-shaped) body with two heads.

The direct head originates from the anterior (front) part of the lower iliac crest. The indirect head originates from the acetabular ridge (near where the femur meets the pelvis). Both attach at the base of the patella (kneecap). The rectus femoris partially covers the other three quadriceps.

The rectus femoris is responsible for flexion at the hip joint. This occurs when you tip the torso forward or when you bring the thighs closer to your torso. Activities that involve hip flexion include walking, running, stepping up onto a bench or staircase, and standing up. The rectus femoris is also involved in extension at the knee joint.

Vastus Lateralis

The vastus lateralis is another prominent muscle on the front of the thigh. In fact, it is the largest of the quadriceps muscles. It originates at the upper part of the outside of the head of the femur and then attaches to the outside of the patella (kneecap). In well-developed athletes, you'll notice it prominently on the outside (lateral side) of the thigh. This quadriceps muscle is also responsible for extending the knee.

Vastus Medialis

The vastus medialis is similar to the vastus lateralis but it runs along the inside (medial) of the front of the thigh instead of the outside. It originates at the inside of the head of the femur and runs down the leg, attaching to the medial (inside) base of the patella. It works together with the other muscles to create flexion at the knee joint.

Vastus Intermedius

The vastus intermedius lies under the rectus femoris and between the vastus lateralis and vastus medialis. It originates at the upper portion of the front (anterior) and side (lateral) surfaces of the femur. It runs down the middle of the thigh and attaches at the top side part of the kneecap. It also forms the deep portion of the quadriceps tendon. Like the other quadriceps muscles, it helps to create flexion at the knee joint.


The primary function of the quadriceps is to extend (straighten) the knee. The rectus femoris also stablizes and creates flexion at the hip joint. The vastus medialis also adducts the thigh (moves the thigh towards the midline of the body) and stabilizes the kneecap.

In simple terms, you use the quads whenever you straighten a bent knee. In everyday life, they help you get up from a chair, walk, climb stairs, and squat. You extend the knee when you kick a ball, run, stand up, and perform other activities where you need to straighten the legs at the knee joint.

During walking and running the quads are active at the onset of a stride and get used significantly when going downhill. They get a real workout with cycling and are used in jumping and in sports like basketball, football, or soccer.

The quadriceps are antagonists to the hamstring and gluteal muscles, which do more of the heavy work in running and walking. Antagonists are muscles that oppose each other during a movement—in effect balancing the function of the joint.

If one muscle group is tight, it can have an effect on the opposing muscles. For example, those with tight quads may have underdeveloped hamstring and gluteal muscles. One way to relieve the tight quads is to develop stronger hamstrings and glutes to achieve balance.

Strength Exercises

Sprinting, cycling, and stair climbing are different ways to strengthen the quadriceps muscles with cardiovascular activities. But most people who are interested in building stronger quads head to the weight room.

There are many different ways to strengthen the quads. Compound exercises are those movements that involve more than one joint and muscle group. Just a few compound exercises for the quadriceps include:

You can also do isolation exercises for the quads. Isolation exercises are those movements that involve just one joint. A common isolation exercise for the quads is the leg extensions and exercise machines for the inner thigh and outer thigh.


Tight quadriceps can cause an imbalance with the hamstrings and gluteal muscles. When this happens, it is not uncommon to experience hip or lower back pain. Runners and cyclists may experience tight quads. Warming up at an easy pace can help relieve the tightness.

But you can also participate in regular flexibility training to keep the quads from getting too tight. Simple quadricep stretches can be performed standing or lying down. It is generally best to do them at the end of a workout or at least when the body is warm.

Injury Prevention

Strengthening the quadriceps muscles can help to prevent injury in the lower body. For example, making sure that the quads are well-developed can help to decrease the risk of injuries such as patellar tendinopathy, a common condition that causes pain in the front of the knee.

Strong quads are also important for the prevention of anterior cruciate ligament (ACL) injuries. The quadriceps are also involved in the rehabilitation of these injuries, so having strong muscles in that area may also help you to heal faster. 

Runners often develop an imbalance between strong hamstring muscles and less-developed quadriceps. A pulled or strained quad muscle may result, often during a sudden acceleration, sprint, or kicking action. This is one of the reasons that runners are often advised to participate in strength training in addition to their endurance activities.

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  1. Chandler TJ, Brown LE. Conditioning for Strength and Human Performance, Third Edition. Routledge; 2018.

  2. Kaeding CC, Borchers JR. Hamstring and Quadriceps Injuries in Athletes, A Clinical Guide. Springer; 2014.

  3. University of Washington Department of Radiology. Rectus femoris. 2020

  4. University of Washington Department of Radiology. Vastus lateralis. 2020

  5. University of Washington Department of Radiology. Vastus medialis. 2020

  6. University of Washington Department of Radiology. Vastus intermedius. 2020

  7. Kopydlowski N.J., Weber A.E., Sekiya J.K. "Functional Anatomy of the Hamstrings and Quadriceps." In: Kaeding C., Borchers J. (eds) Hamstring and Quadriceps Injuries in Athletes. Boston, MA: Springer; 2014:1–14.

  8. Miao P, Xu Y, Pan C, Liu H, Wang C. Vastus medialis oblique and vastus lateralis activity during a double-leg semisquat with or without hip adduction in patients with patellofemoral pain syndromeBMC Musculoskelet Disord. 2015;16:289. doi:10.1186/s12891-015-0736-6

  9. Loyola University Medical Education Network. Vastus medialis.

  10. Morgan S, Janse van Vuuren EC, Coetzee FF. Causative factors and rehabilitation of patellar tendinopathy: A systematic reviewS Afr J Physiother. 2016;72(1):338. doi:10.4102/sajp.v72i1.338

  11. Bodor M. Quadriceps protects the anterior cruciate ligament. J Orthop Res. 2001;19(4):629-33. doi: 10.1016/S0736-0266(01)00050-X.