The Anatomy of the Quadriceps Muscles

Quad muscles, or quadriceps femoris muscles, are a group of four muscles that cover the front and sides of your thighs. The quadriceps are some of the largest and most powerful muscles in your body. They provide the force you need to run, walk, jump, kick, and complete most lower-body movements.

The main function of the quadriceps is to keep your knee stable and help you straighten it. Because of the amount of stress placed on them, your quads can be prone to injury. Treatment will vary depending on the specific injury, but may include the RICE (rest, ice, compression, elevation) method, medication, physical therapy, and surgery.

This article explains the anatomy and function of the quadriceps muscles. It also covers some of the most common injuries that affect the quads, along with how those injuries are treated.

Anatomy

Quadriceps femoris muscle translates to "four-headed muscle of the femur" in latin. It gets this name because of the four separate muscles that make up the quadriceps group in each of your thighs, all of which cover the front and sides of the femur (thigh bone).

The four separate quadriceps muscles are:

• Vastus intermedius
• Vastus medialis oblique (VMO)
• Vastus lateralis
• Rectus femoris

Location

The rectus femoris is in the middle of the thigh and covers much of the other three quad muscles. This is the most superficial quad muscle, meaning that it is closest to the surface of your skin.

While the rectus femoris starts in the top part of the the ilium (hip bone) and stretches down the thigh, the other quad muscles each start at different parts of the femur.

The vastus lateralis is on the outer side of the thigh. It is the largest and most powerful quad muscle.

The vastus medialis is on the inner part of the thigh. It is the smallest quad muscle.

The vastus intermedius is between the vastus lateralis and vastus medialis. It is the deepest quad muscle, covered entirely by the rectus femoris.

All four of the quad muscles come together just above the patella (kneecap). They are attached to the top of the patella via the quadriceps tendon.

At the bottom of the patella, the quadriceps tendon becomes the patellar tendon, which attaches the patella to the tibial tuberosity—a bony structure below the front of the knee that acts as the knee's lever.

Structure

Like all muscles in your body, the quadriceps muscles are made of tightly bound muscle fibers. The muscle fibers themselves are made of protein. This explains why body builders and other athletes eat more protein to build and maintain their muscles.

Muscle fibers can be divided into two types:

• Slow-twitch fibers fibers burn energy slowly and steadily so that you can stand, walk, and do other low-intensity activities for long periods of time.
• Fast-twitch fibers tire more quickly because they power intense movements that require big bursts of energy, like sprinting and jumping.

All people have a mix of slow and fast-twitch fibers in their quads. But some people may naturally have a higher amount of one type.

For example, a person who is a natural sprinter may have more fast-twitch muscle fibers in their quads, while someone who is a great endurance runner may have more slow-twitch muscle fibers in their quads. It is possible to build more of a particular fiber type with targeted training.

About two-thirds of muscle fibers that make up the vastus lateralis are fast-twitch, which explains why it is your most powerful quad muscle. From a practical standpoint, if you want to grow your vastus lateralis, you should do more explosive training exercises, like sprints and jump squats.

Function

If you sit in a chair and straighten your knee a few times, you can see and feel the quads in action on the front part of your thigh. When your quads contract, they straighten your leg at your knee joint, enabling you to run, walk, jump, climb stairs, stand from a seated position, and so much more.

Since the quadriceps extend over the kneecap, they also help keep it in its proper position in a groove at the end of your thigh bone. All quad muscles work to keep your knee stable. But the rectus femoris is the only quad muscle that crosses the hip joint and can assist in upward bending (flexion) of your hip.

The vastus medialis oblique is especially important for stabilizing your knee joint and controlling how your patella moves. If the VMO is weak or does not function properly, the patella can rub against the side of the groove. Over time, this can damage knee cartilage and cause the joint lining to get inflamed.

Associated Conditions

Many sports and physical activities place a great deal of stress on the quads, making the quad muscles themselves prone to injury. The rectus femoris is the most frequently injured quadriceps muscle simply because it is closest to the skin and covers the other quad muscles.

If you injure your quadriceps muscle(s), you may have difficulty with functional mobility, or the ability to perform the everyday tasks of living. For example, you may be surprised to learn that your quadriceps muscles help you move around in bed. They contract to help you scoot your bottom while lying down, and they can help you roll from one side to the other.

Since your quads keep your kneecap in the correct position, weak or injured quad muscles can put the kneecap at risk for injury as well.

Injuries that can affect your quad muscles and/or kneecaps include:

Quadriceps contusion: The most common quadriceps injury is a contusion (bruise). It happens when your thigh gets hit very hard, causing the quad muscle(s) to tear and bleed. As a result, the surrounding muscle gets inflamed. Severe quad contusions can make it very painful to extend the knee.

Quadriceps strain: This injury happens when you overstretch your quadriceps muscle, causing the muscle fibers to tear. You might hear a strain referred to as "pulling" the muscle, because of the pulling sensation it causes in the front of the thigh.

A strain causes pain and swelling in the muscle. There can also be bruising and temporary loss of strength in the strained muscle. If the tear is severe enough, the quads can separate from the kneecap, making it impossible for you to straighten your knee.

Quadriceps tendonitis: Tendonitis is inflammation of a tendon, the connective tissues that attach muscles to bones. Quadriceps tendonitis causes inflammation in the quad muscles and quad tendon.

This is a common overuse injury, resulting from excessive stress on the knee joints and/or quad muscles over time. It causes pain and swelling above the kneecap, which worsens when you move your knee.

Kneecap dislocation: In this injury, your quad muscle tears off the bone just below the kneecap, causing the kneecap to slip (dislocate) from its groove. This is almost always the result of trauma, such as a sports injury or fall.

When the injury occurs, there may be a "popping" sensation and severe knee pain. The knee tends to swell up quickly, making it very difficult (and painful) to straighten the joint.

Patellofemoral stress syndrome: Excessive running and jumping places chronic stress on the knee joint, creating inflammation under the kneecap. When this happens, the quads are unable to keep the kneecap stable, causing it to rub against its groove.

This chronic overuse injury leads to pain and swelling in the front of the knee and under the kneecap that worsens when you walk downstairs or downhill.

Iliotibial band syndrome: The iliotibial band is a long tendon that stretches down the outside of your thigh, all the way from your hip bone to your shin bone. In iliotibial band syndrome, this tendon rubs against your hip or knee bones, causing pain and inflammation on the outside of the knee.

This can happen if your quads are especially tight or weak, or if your hamstrings are weaker than your quadriceps. Excessive bending at the knee, as is needed to run or cycle, can cause it too.

Quadriceps paresis and paralysis: Quadriceps paresis (muscle weakness) or paralysis (total loss of muscle function) most commonly occur due to a spinal cord injury or stroke. A pinched nerve in the lower spine, such as the L3 vertebra, can also lead to quadriceps paresis. This condition leads to severe knee instability and disability.

Compartment syndrome: This rare, painful, and possibly life-threatening condition is most commonly caused by sports injuries. The syndrome can develop hours after a direct blow to the thigh causes a quadriceps contusion and/or vascular (vein) damage.

As pressure builds up in the quad, blood flow to the area becomes restricted, leading to quad muscle and nerve damage. In severe cases, the damage may be irreversible.

Treatment

Treatment depends on the specific issue that is compromising the quadriceps muscle(s). The possibilities range from rest and rehabilitation exercises to medication and surgery.

Quadriceps contusion: Most quad contusions are minor and heal on their own within a few weeks. Severe contusions can take up to six weeks to heal, though it can take longer if you continue to put stress on the bruised muscle.

Contusions are treated with the RICE method, which stands for rest, ice, compression, and elevation. This is the most effective way to reduce swelling, ease pain, and heal the contusion.

Quadriceps strain: Mild to moderate strains may take up to three weeks to heal, so long as you give your strained quad enough rest from physical activities. The RICE method can also be used to ease pain and swelling and speed the healing process along.

If the strain is more severe, your healthcare provider may recommend physical therapy.

Quadriceps tendonitis: Early treatment for quadriceps tendonitis includes RICE and nonsteroidal anti-inflammatory drugs (NSAIDs) like Advil (ibuprofen) and Aleve (naproxen).

Physical therapy is often recommended for tendonitis both to decrease pain and minimize further damage. Bracing or taping the patella can reduce pain during daily activities. Custom orthotics (shoe inserts) can be worn to help keep your knee in its proper alignment.

Kneecap dislocation: Dislocated kneecaps often pop themselves back into place. Even so, you should still see your healthcare provider to make sure.

If the kneecap has not corrected itself, your provider will manipulate it back into place. They will take an X-ray of your knee to check for fractures or ligament tears.

You may be given a brace to stabilize your knee as well as physical therapy. If your knee has dislocated several times or if there is a fracture or ligament tear, you may need surgery. This will also be followed by use of a knee brace and physical therapy.

Patellofemoral stress syndrome: Treatment for PFSS begins with RICE. You will need to rest your knee and avoid activities that make your pain worse. NSAIDs can be taken as needed to reduce pain and swelling.

Physical therapy is often recommended to strengthen the muscles that support the knee and prevent further issues. A physical therapist may give you a knee brace or show you how to tape your knee to reduce pain while you exercise. Orthotic shoe inserts can also help keep your knee stable.

Iliotibial band friction syndrome: Treatment for iliotibial band friction syndrome begins with resting the knee, avoiding activities that worsen the pain, and icing the outside of the knee. Taking NSAIDs can help reduce inflammation and pain.

If your pain is severe, your healthcare provider may recommend cortisone shots to reduce inflammation. In some cases, physical therapy is advised.

Surgery may be recommended if other therapies fail to improve your condition within six months. Surgery involves removing the part of the iliotibial band that is rubbing against the femur.

Quadriceps paresis or paralysis: Recovery from paresis or paralysis largely depends on what caused the injury and how severe it is.

Physical therapy is recommended to minimize the effects of paresis and restore nerve and muscle function. A therapy called neuromuscular electrical stimulation (NMES), in which electrical impulses stimulate the quad muscles to contract, may improve muscle function.

Knee braces and foot orthotics are often used to stabilize the knee. An assistive device, such as a cane or walker, can help those with paresis move around safely.

Emergency surgery may be required to treat the cause of the brain injury.

Compartment syndrome: Acute compartment syndrome must be treated with an emergency surgery called a fasciotomy. For this procedure, the surgeon will cut open your skin and the tissues surrounding the affected quad muscles to rapidly relieve the pressure that has built up there.

Following surgery, physical therapy will be necessary to rebuild strength, flexibility, and range of motion in your leg. You will need to take ample rest from physical activities and use the RICE method frequently. It can take up to four months to recover from compartment syndrome completely.

What Does PT for the Quads Entail?

The main types of physical therapy exercises used to help improve the function and health of your quadriceps include:

• Strength: Since the quadriceps muscles cross both the hip and the knee, exercises that involve the knee and the hip are essential to improve quad strength. Simple knee strengthening exercises will target the quads, and advanced hip strengthening exercises will also include quite a bit of quadriceps work.
• Flexibility: There are many easy stretches to do to improve the flexibility of your quadriceps muscles. It's important to be gentle and pay attention to your pain so that you do not overstretch your knee and cause further injury.
• Balance and proprioception: Balance and proprioception (body position awareness) exercises often focus on the quadriceps since these are essential in keeping you upright and balanced. Basic balance exercises can also help to prevent falls, and advanced balance exercises may be used to help treat quad injuries and knee pain.

Your physical therapist can offer suggestions as to the best exercises to help your specific condition.

Summary

The quadriceps femoris is a group of four muscles located in each of your thighs. These are very powerful muscles that play a key role in most physical activities that involve the lower body, such as running, jumping, climbing stairs, and more.

Because the quad muscles help straighten and stabilize the knee, injuring one or more of them can cause your kneecap to feel unstable. Knee instability is often a consequence of quad injuries. Thus, treatment often focuses on both restoring quad strength and knee stability.

A Word From Verywell

If you feel pain in the front of your thigh after an injury, you may have done something to your quadriceps.

Often, injuries to the quads are easy to rehab; a little rest and some stretching may be all you need. Other times, a quadriceps injury can be serious, so check in with your healthcare provider in you have injured the front of your thigh.