Logan Steele
The quadriceps femoris muscle, commonly known as the quad muscle, is the strongest muscle in the human body. It is located in the anterior compartment of the thigh and is comprised of four individual muscles: the rectus femoris, vastus medialis, vastus lateralis, and vastus intermedius. The quad muscle is responsible for extending the leg at the knee joint and flexing the thigh at the hip joint, enabling movements such as kicking, running, and jumping. The name quadriceps femoris translates to “four-headed muscle” from Latin, reflecting the four distinct muscles that unite to form this powerful muscle group.
| Characteristics | Values |
|---|---|
| Location | Front of the thigh |
| Function | Extends the leg at the knee joint and flexes the thigh at the hip joint |
| Muscle Components | Rectus femoris, vastus medialis, vastus lateralis, vastus intermedius, tensor vastus intermedius, and articularis genus muscle |
| Innervation | Femoral nerve (L2, L3, L4) |
| Blood Supply | Femoral artery |
| Common Injuries | Strains, contusions, cuts, tendonitis |
| Strength Testing | Resisted knee extension with the hip flexed and extended |
| Myoelectric Balance | Essential for correct movement of the patella |
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What You'll Learn
Rectus femoris
The rectus femoris is one of the four muscles that make up the quadriceps femoris, or \"quad muscle", which is the strongest muscle in the human body. The other three muscles are the vastus medialis, the vastus intermedius, and the vastus lateralis. The rectus femoris is the only muscle in the quadriceps group that crosses both the hip and knee joints.
The rectus femoris is located in the anterior or front middle compartment of the thigh. It is the most superficial muscle in the anterior thigh compartment and is nearly vertically oriented. The word rectus means "straight" in Latin, and the rectus femoris runs straight down the thigh. It is superior and overlying the vastus intermedius muscle and the superior-medial part of the vastus lateralis and vastus medialis. The rectus femoris is also known as the "kicking muscle" because it is involved in activities that require forceful knee extension.
The rectus femoris is a two-way acting muscle, as it crosses over the hip and knee joints. It functions to extend the knee and assist the iliopsoas in hip flexion. It is a weaker hip flexor when the knee is extended because it is already shortened and thus suffers from active insufficiency. The action of extending the knee from a seated position is primarily driven by the other three muscles of the quadriceps femoris.
The rectus femoris is prone to injury, especially at the tendon that attaches to the patella or kneecap, or in the muscle itself. This is because it crosses both the hip and knee joints. Symptoms of a rectus femoris strain include a sudden sharp pain at the front of the hip or in the groin, swelling and bruising, and an inability to contract the muscle with a full tear. The injury is usually caused by a forceful movement related to sprinting, jumping, or kicking and is common in sports such as football or soccer.
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Vastus intermedius
The vastus intermedius is one of the four muscles that make up the quadriceps femoris, or quad muscle group. The quadriceps femoris is the strongest muscle in the human body, allowing us to straighten our knees and flex our thighs at the hip joint. The three other muscles that form the quadriceps femoris are the rectus femoris, vastus medialis, and vastus lateralis.
The vastus intermedius is a recently discovered muscle that sits between the vastus lateralis and vastus medialis. It arises from the upper two-thirds of the front and lateral surfaces of the femur and the intermuscular septum. The vastus intermedius is located in the middle of the thigh, beneath the rectus femoris. Its fibres end in a superficial aponeurosis, which forms the deep part of the quadriceps femoris tendon, which attaches the muscles to the kneecap.
The vastus intermedius is the deepest of the quadriceps muscles and is difficult to stretch once maximum knee flexion is attained. It is also difficult to palpate. The vastus intermedius cannot be stretched by hip extension, nor can it be manipulated with massage therapy to stretch the fibres sideways.
The quadriceps femoris muscle is the most powerful extensor of the knee. The most common injuries to the quadriceps femoris are strains, or "pulled quads," which result from overstretched muscle fibres. Thigh strains can range from mild to severe, with the most severe cases resulting in a complete tear of the quad tendon from the kneecap.
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Vastus lateralis
The vastus lateralis is the largest of the four muscles that make up the quadriceps femoris. It is also the most powerful part of the muscle group. The other three muscles are the rectus femoris, vastus intermedius, and vastus medialis. The vastus lateralis is also known as the vastus externus.
The vastus lateralis is located on the lateral side of the thigh. It connects the thigh bone (femur) to the kneecap (patella). It runs along the outside of the thigh. The muscle is used to extend the knee joint, moving the lower leg forward. It also helps to stabilise the knee joint, working in conjunction with the vastus medialis.
The vastus lateralis arises from a series of flat, broad tendons attached to the femur. It ultimately joins with the other muscles that make up the quadriceps in the quadriceps tendon, which travels over the knee to connect to the tibia. The muscle is supplied by the lateral circumflex femoral artery, which has three main branches: ascending, transverse, and descending. The muscle is innervated by the muscular branches of the femoral nerve (L2, L3, and L4).
The vastus lateralis may have two insertional heads in approximately 60% of specimens. These two heads are referred to as the vastus lateralis long head (VLL) and the vastus lateralis obliquus (VLO). The VLL typically inserts at an angle between 10 degrees and 17 degrees, while the VLO has an insertional variation between 26 degrees and 41 degrees.
The vastus lateralis is the recommended site for intramuscular injection in infants less than 7 months old and those unable to walk, with loss of muscular tone.
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Vastus medialis
The vastus medialis is a teardrop-shaped muscle in the front of the thigh. It is one of the four muscles that make up the quadriceps group, the others being the vastus lateralis, vastus intermedius, and rectus femoris. It is the smallest of the quad muscles.
The vastus medialis is located in the anterior compartment of the thigh, originating from several landmarks of the proximal femur, including the inferior part of the intertrochanteric line, pectineal line of femur, medial lip of linea aspera, and proximal half of the medial supracondylar line. It then descends obliquely through the thigh, with its fibres spiralling around the long axis of the muscle. The lowermost fibres lie in a near-horizontal plane, forming a noticeable bulge above the medial side of the patella.
The vastus medialis has several functions. Firstly, it helps to extend the knee, working in tandem with the other three quad muscles and the articularis genu. It also helps to stabilise the kneecap, keeping it properly aligned as the leg is straightened. Additionally, the vastus medialis contributes to the correct tracking of the patella, helping to prevent patellar dislocation.
The vastus medialis is vulnerable to injuries such as strains, which can occur due to the muscle's role in bearing weight and absorbing the force of impact from activities like running and jumping. A common injury is patellofemoral pain syndrome (PFPS), which occurs when the cartilage under the kneecap is damaged due to overuse or injury. This can cause knee pain that worsens when using stairs or squatting. Treatment for a vastus medialis injury typically involves rest, ice, compression, and elevation of the leg, along with pain relievers. Physical therapy and surgery may be necessary in severe cases.
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Articularis genus muscle
The articularis genus muscle (also known as the subcrureus muscle) is a small skeletal muscle located in the anterior compartment of the thigh, just above the knee. It arises from the anterior surface of the lower part of the femur, deep to the vastus intermedius, and from the deep fibres of the vastus intermedius. The muscle is flat, wispy, and highly variable, sometimes consisting of several distinct muscle bundles. Its width typically ranges from 1.5 to 3 cm.
The articularis genus muscle is closely connected with the vastus intermedius and vastus medialis muscles. The muscle bundles of the articularis genus are organised into three main layers: superficial, intermediate, and deep. The bundles of the superficial layer and 60% of the intermediate layer originate from the vastus intermedius and the anterior and anterolateral surfaces of the femur. The deep layer and the remaining 40% of the intermediate layer arise solely from the anterior surface of the femur.
The distal attachment sites of the articularis genus include the proximal and posterior walls of the suprapatellar bursa and the synovial membrane of the medial and lateral aspects of the knee joint capsule. The muscle is supplied by the lateral femoral circumflex artery and innervated by branches of the femoral nerve (L2-L4).
The function of the articularis genus muscle is not yet fully understood. However, it is speculated to be involved in coordinating the movement of the suprapatellar bursa during knee flexion and extension. Some studies suggest that the muscle retracts the suprapatellar bursa during knee extension, preventing the impingement of the synovial membrane between the patella and the femur. However, the architectural parameters of the muscle indicate that it may not generate enough force to fulfil this function.
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Frequently asked questions
The quadriceps femoris is formed of four muscles: the rectus femoris, vastus medialis, vastus lateralis, and vastus intermedius.
The quadriceps femoris is the strongest muscle in the human body and is the most powerful extensor of the knee. It is the only muscle of the quadriceps to cross both the hip and knee joints.
The four muscles of the quadriceps femoris merge into a single tendon, the quadriceps femoris tendon, which attaches to the kneecap.
