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Extension and flexion are the basic ways the body moves at its joints. Extension is the backward movement of the body, increasing the angle between two body parts or bones. For example, extension occurs when straightening the elbow or knee or bending the wrist or spine backward. The quadricep group and the articularis genu are the most significant contributors to knee extension. Extension is essential in athletic activities and gym training for muscle and strength gains.
| Characteristics | Values |
|---|---|
| Definition | Extension is the straightening of a joint that increases the angle between two body parts. |
| Direction | Extension is usually directed backward. |
| Exceptions | The knee joint and exercises involving the bending of the knee, such as a hamstring curl. |
| Joint Angle | Extension increases the angle between bones. |
| Examples | Nodding the head, straightening the elbow or knee, bending the wrist or spine backward. |
| Muscles Involved | Triceps brachii, anconeus, quadricep group (rectus femoris, vastus lateralis, vastus intermedius, vastus medialis), articularis genu. |
| Hyperextension | Occurs when a joint extends beyond its natural range of motion. |
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What You'll Learn
Extension at the knee joint
The knee joint is a bi-condylar type of synovial joint, which allows mainly for flexion and extension, and a small degree of medial and lateral rotation. Flexion and extension are movements that affect joint angle. Flexion is the bending of a joint that decreases the angle between two segments of the body. Extension is the opposite of flexion; it is the straightening of a joint that increases the angle between two body parts. Both are essential in athletic activities and gym training for muscle and strength gains.
The quadricep group (rectus femoris, vastus lateralis, vastus intermedius, vastus medialis) and the articularis genu are the most significant contributors to knee extension. The articularis genu is a small muscle or muscle group with several variations of structure. It is found beneath the vastus intermedius and is often distinct enough from the v. intermedius, but can be seen blended into the muscle. It has also been found to be in several muscular bundles. However, it consistently has been found to arise from the anterior surface of the distal femur, just proximal to the epicondyles, and inserting into the synovial membrane of the knee joint. During knee extension, the articularis genu pulls the suprapatellar bursae of the knee, and also helps the synovial membrane not to become caught between the patella and femur within the joint.
The iliotibial tract (ITB) and tensor fascia latae (TFL) also play a role in knee extension. The ITB is an active knee extensor from 20 to 30 degrees of flexion to full extension. The TFL works with the ITB to stabilize the knee when it is in full extension. The knee extensors are essential for daily activities, such as climbing stairs, getting up from a chair, and walking, and are important in many sports, such as kicking, jumping, cycling, and running.
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Extension and flexion
Flexion and extension are terms used to describe the basic ways the body moves at its joints. They are movements that affect the angle of the joints.
Flexion is the bending of a joint that decreases the angle between two segments of the body. A simple way to remember this is to associate 'flexing' with 'bending'. For example, when you bend your elbow, you are flexing it by bringing your humerus closer to your radius. Neck flexion is another example, where the head is dropped forward, bringing the chin down towards the chest, decreasing the angle at the front of the body. Lateral flexion is also possible, where the body flexes sideways.
Extension is the opposite of flexion; it is the straightening of a joint that increases the angle between two body parts. Extension is backward (posterior motion) and increases the angle at the front of the body. For example, when you straighten your elbow after bending it, that is extension. Extension can also go beyond straightening into hyperextension, where the joint extends beyond its natural range of motion. An example of hyperextension is when someone leans far back and hyperextends their spine at the top of a deadlift.
Both flexion and extension are essential in athletic activities and gym training for muscle and strength gains. It is important to include a balance of flexion and extension moves in a training routine to build balanced strength and muscle while minimising the risk of injury. For example, performing both the biceps curl (flexion) and triceps kickback (extension) each week will strengthen both sides of the arms.
Knee extension is a specific type of extension that involves the lowering of the leg at the knee joint from a flexed knee position, straightening the knee and entire leg. The quadricep group and the articularis genu are the most significant contributors to knee extension.
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Extensor muscles in the foot
Extension is the straightening of a joint that increases the angle between two body parts. Flexion and extension are simple concepts that are essential in athletic activities and gym training for muscle and strength gains. The muscles acting on the foot can be divided into two distinct groups: extrinsic and intrinsic muscles. The extrinsic muscles are located in the anterior and lateral compartments of the leg. The intrinsic muscles, on the other hand, are located in the plantar aspect (sole) of the foot. There are ten intrinsic muscles in the sole of the foot, which act collectively to stabilise the arches of the foot and individually to control the movement of the digits.
The extensor digitorum longus is a pennate muscle situated at the lateral part of the front of the leg. It arises from the lateral condyle of the tibia, the upper three-quarters of the anterior surface of the body of the fibula, the upper part of the interosseous membrane, the deep surface of the fascia, and the intermuscular septa. The extensor digitorum longus passes under the superior and inferior extensor retinaculum of the foot in company with the fibularis tertius, and divides into four slips, which run forward on the dorsum of the foot, and are inserted into the second and third phalanges of the four lesser toes. The extensor digitorum longus is the only muscle that can extend the little toe.
The extensor digitorum brevis muscle results in dorsiflexion, or hyperextension of the second to fourth toes, occurring at the metatarsophalangeal joints of the same digits. The extensor hallucis brevis muscle similarly causes dorsiflexion of the metatarsophalangeal joint of the big toe. The dorsal foot muscles generally have no insertion at the little toe.
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Extension and abduction
Flexion and extension are movements that affect joint angles. Extension is the straightening of a joint that increases the angle between two body parts. The knee joint is a good example of this. Knee extension is the lowering of the leg at the knee joint from a flexed knee position, thus straightening the knee and the entire leg. The quadricep group and the articularis genu are the most significant contributors to knee extension. The articularis genu is a small muscle or muscle group found beneath the vastus intermedius.
Hyperextension occurs when a joint extends beyond its natural range of motion. This can result in discomfort and injuries. An example of hyperextension is when someone leans far back and hyperextends their spine at the top of a deadlift.
Abduction and adduction are motions of the limbs, hand, fingers, or toes in the coronal (medial-lateral) plane of movement. Abduction moves the limb laterally away from the midline of the body, while adduction is the opposing movement that brings the limb toward the body or across the midline. For example, abduction is raising the arm at the shoulder joint, moving it laterally away from the body, while adduction brings the arm down to the side of the body.
Abduction and adduction movements are seen at condyloid, saddle, and ball-and-socket joints. Circumduction is the movement of a body region in a circular manner, in which one end of the body region being moved stays relatively stationary while the other end describes a circle. It involves the sequential combination of flexion, adduction, extension, and abduction at a joint. This type of motion is found at biaxial condyloid and saddle joints, and at multiaxial ball-and-sockets joints.
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Extension and hyperextension
Flexion and extension are movements that affect joint angles. They are basic ways the body moves at its joints. Flexion is the bending of a joint that decreases the angle between two segments of the body. Extension is the opposite of flexion; it is the straightening of a joint that increases the angle between two body parts. For example, in the upper limb, all anterior-going motions are flexion, and all posterior-going motions are extension.
Extension at the knee joint is a complex topic. The quadricep group (rectus femoris, vastus lateralis, vastus intermedius, and vastus medialis) and the articularis genu are the most significant contributors to knee extension. The articularis genu is a small muscle or muscle group that arises from the anterior surface of the distal femur, inserting into the synovial membrane of the knee joint. During knee extension, the articularis genu pulls the suprapatellar bursae of the knee and helps the synovial membrane from becoming caught between the patella and femur within the knee joint.
Hyperextension occurs when a joint extends beyond its natural range of motion, whereas extension refers to the straightening of a joint within its normal range. For example, knee extension can occasionally overextend anteriorly, straightening past the neutral, weight-bearing stance into hyperextension. Pushing a joint beyond its natural ability to move can lead to discomfort and injuries. For instance, leaning far back and hyperextending the spine at the top of a deadlift can cause discomfort and injuries.
In resistance training, several exercises can strengthen the posterior chain, which is essential for athletic performance and injury prevention. The Reverse Hyperextension (RHE) and the Back Extension (BE) are two exercises that target the hip extensors and the erector spinae. The RHE keeps the upper body immobile, while the BE allows the same muscle groups to be worked with the lower body immobile. The RHE has a greater range of motion between the trunk and thigh compared to the BE, and it results in lower lumbar flexion.
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Frequently asked questions
Muscle extension is the straightening of a joint that increases the angle between two body parts.
An example of muscle extension is the straightening of the knee joint.
The quadricep group (rectus femoris, vastus lateralis, vastus intermedius, and vastus medialis) and the articularis genu are the most significant contributors to knee extension.
Muscle flexion is the opposite of muscle extension. It is the bending of a joint that decreases the angle between two segments of the body.
An example of muscle flexion is a biceps curl.
