Dominic Stone
Two-jointed muscles, also known as biarticular muscles, cross two joints in the body and have an action at each of the joints. They are more complex in their functions compared to single-joint muscles. Examples of two-jointed muscles include the hamstrings, which cross the hip and knee joints, and the gastrocnemius muscle of the calf, which crosses the knee and ankle joints. Two-jointed muscles can produce movement at multiple joints, but their force capacity is reduced when both joints are in motion simultaneously.
| Characteristics | Values |
|---|---|
| Definition | Muscles that cross two joints |
| Alternative Name | Biarticular muscles |
| Examples | Hamstrings, gastrocnemius, rectus femoris, biceps |
| Function | More complex than single-joint muscles; can produce movement at more than one joint |
| Anatomy | Origin (proximal attachment) and insertion (distal attachment) play a role in determining function |
| Mechanics | Can transfer mechanical power between distal and proximal joints; direction and magnitude depend on anatomy, muscle activity, and joint angles |
| Advantages | Can put the joint into a four-bar linkage, allowing contraction of muscles at one joint to move the other by a fixed amount |
| Disadvantages | Performing both functions simultaneously reduces the composite force capable of being produced at both joints |
| Insufficiency | Active and passive insufficiency can occur when a multi-joint muscle cannot apply adequate force or lengthen to allow full ROM of all joints |
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What You'll Learn
Hamstrings cross the hip and knee joints
The hamstrings are a group of three muscles—the biceps femoris, semitendinosus, and semimembranosus—located at the back of the thigh. They are skeletal muscles, which means that they are under your conscious control. They are responsible for many daily activities, such as walking, climbing stairs, running, jumping, and performing squats.
The hamstrings cross two joints, the hip and the knee, and are therefore known as biarticular muscles. They contract when the knee is bent and lengthen when the knee is extended. They also extend the hip when the trunk is fixed. The hamstrings are involved in knee flexion and hip extension. The short head of the biceps femoris, however, is a single-joint muscle that only crosses the knee joint.
The hamstrings are prone to injury, especially in sports that require quick stops and starts, such as soccer and football. They are also susceptible to injury when the knee is bent in a deep squat position. To avoid hamstring injuries, it is important to properly warm up and stretch before physical activity and to rest the muscles when feeling pain or fatigue.
The hamstrings play a crucial role in human movement, and their function is complex. They can contract isometrically, allowing the contraction of muscles at one joint to move the other by a fixed amount. They can also transfer mechanical power between distal and proximal joints, although the direction and magnitude of this transfer depend on various factors, such as anatomy and muscle activity level.
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Rectus femoris crosses the hip and knee joints
The rectus femoris is a muscle in the quadriceps group. It is the only muscle in the quadriceps group that crosses two joints, the hip and the knee. It originates at the iliac crest (pelvis) and inserts on the tibia (lower leg).
The rectus femoris acts with iliopsoas to produce hip flexion, especially if the knee is flexed. During gait, as a hip flexor, it acts with the iliopsoas in the "Toe off" phase. Together with other muscles that are part of the quadriceps femoris, it facilitates knee extension. In the terminal swing phase, the rectus femoris acts as an extensor of the knee, generating the force needed for loading (foot-flat phase) in the stance phase. The rectus femoris is more efficient in movement combining hip hyper-extension and knee flexion or from a position of knee extension and hip flexion, for example, kicking a soccer ball.
The rectus femoris is also known as the "kicking muscle" for its involvement in activities involving forceful knee extension. It is the anterior thigh compartment's most superficial and nearly vertically oriented muscle. This muscle has two origins. The "direct head" originates from the anterior inferior iliac spine, while the superior acetabular ridge is the origin of the "indirect head".
A markedly shortened rectus femoris is suggested by knee flexion of less than 80 degrees or by marked prominence of the superior patellar groove. Acute rectus femoris strain typically presents with swelling and moderate to severe pain in the groin or anterior aspect of the hip. Knee extension is also impaired.
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Gastrocnemius crosses the knee and ankle joints
The gastrocnemius muscle is a two-jointed muscle that crosses the knee and ankle joints. It is a superficial two-headed muscle located in the back part of the lower leg. The muscle gets its name from the Latin, derived from the Greek γαστήρ (gaster), meaning 'belly' or 'stomach', and κνήμη (knḗmē), meaning 'leg', thus earning the name 'stomach of the leg' due to the bulging shape of the calf.
The gastrocnemius is one of the two main muscles that make up the calf muscle, the other being the soleus muscle. Together, these muscles help the body to walk, run, jump, stand on the toes, and flex the foot. The gastrocnemius is the larger of the two calf muscles and is easily visible and palpable on the back of the lower leg.
The gastrocnemius originates on the femur, with the lateral head arising from the lateral condyle and the medial head from the medial condyle. The muscle then extends down the back of the leg and attaches to the Achilles tendon, which inserts onto the heel bone or calcaneus. This fusion of the gastrocnemius and soleus tendons forms the upper part of the tendocalcaneus.
The gastrocnemius is a powerful muscle that provides significant propulsive force during activities such as running, walking, and jumping. It is considered a triarticular muscle, crossing the knee, ankle, and subtalar joints. However, its primary function is as an ankle plantar flexor, as its role in knee flexion is considered secondary.
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Biceps femoris crosses the hip and knee joints
The biceps femoris is a muscle in the posterior compartment of the thigh that crosses two joints: the hip and the knee. It is part of the hamstring muscle group, along with the semitendinosus and semimembranosus muscles. The biceps femoris has two heads, a long head and a short head, that originate from different locations but share the same insertion site at the fibula.
The long head of the biceps femoris originates from the ischial tuberosity of the pelvis, while the short head originates at the linea aspera of the femur. The muscle then runs distally to insert on the proximal part of the fibula. This insertion site is just below the knee joint, allowing the biceps femoris to act on both the hip and knee joints simultaneously.
At the hip joint, the primary action of the biceps femoris is extension and external rotation of the thigh. This movement is strongest when the trunk is bent forward and brought upright. The biceps femoris also assists in stabilizing the pelvis, especially during forward flexion of the trunk.
At the knee joint, the most prominent action of the biceps femoris is flexion, or bending, of the leg. Additionally, when the knee is slightly bent, the biceps femoris acts to produce external rotation of the lower leg. The short head of the biceps femoris acts primarily on the knee joint, while the long head acts on both the hip and knee joints.
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Finger flexors cross the wrist and finger joints
The flexor digitorum profundus is a muscle in the forearm that flexes the fingers. It is considered an extrinsic hand muscle because it acts on the hand while its muscle belly is located in the forearm. The flexor digitorum profundus is the main gripping muscle of the hand. It acts best when the wrist is extended. It is the sole flexor of the distal interphalangeal joint of the second to fifth fingers.
The flexor digitorum profundus also acts as a flexor of the midcarpal (wrist), metacarpophalangeal, and proximal interphalangeal joints of the index, middle, ring, and little fingers. The lumbricals arise from the flexor digitorum profundus tendons and insert into the dorsal extensor expansions of the proximal phalanges. This allows the flexor digitorum profundus muscle to aid the lumbricals in fully extending the fingers at the interphalangeal joints and flexing the fingers at the metacarpophalangeal joints.
The flexor digitorum profundus is supplied by the anterior interosseous artery, which is a branch of the common interosseous artery. The lymphatic drainage of the flexor digitorum profundus is part of the upper limb lymph system, consisting of superficial and deep lymphatic vessels. The superficial vessels around the basilic vein go to the cubital lymph nodes, which are proximal to the medial epicondyle of the humerus.
The flexor digitorum profundus is one of the deep muscles of the anterior compartment (deep volar compartment) of the forearm. It is the most powerful and bulky muscle of the forearm, forming the muscular elevation seen and felt on the posterior surface of the forearm medial to the subcutaneous posterior border of the ulna. The wrist is a complex joint that connects the radius and ulna (the two bones in the forearm) to the carpals in the hand. It allows for the manipulation of objects and provides the dexterity required for fine motor skills.
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Frequently asked questions
A two-jointed muscle (TJM) or biarticular muscle crosses two joints, making it more complex in its functions. Examples include the hamstrings, which cross the hip and knee joints, and the gastrocnemius, which crosses the knee and ankle joints.
Two-jointed muscles can produce movement at more than one joint, which is advantageous for many human movements. They can also transfer mechanical power between distal and proximal joints.
Two-jointed muscles may become inefficient when trying to exert full active or passive motion at both joints simultaneously, leading to active and passive insufficiency. This results in a reduced composite force at the joints.
