Dominic Stone
Biarticular muscles are a type of muscle that extends across two joints, unlike monoarticular muscles, which only extend across one joint. The function of biarticular muscles is complex and depends on their anatomy and the activity of other muscles at the joints they cross. They can be found in the upper and lower extremities of the human body and are most responsive to upper-body pitch perturbations in human standing. Examples of biarticular muscles include the hamstrings, gastrocnemius, and rectus femoris.
| Characteristics | Values |
|---|---|
| Definition | Muscles that cross two joints |
| Examples | Hamstrings, gastrocnemius, rectus femoris, brachioradialis, triceps surae, HAM, RF |
| Function | Complex, depends on anatomy and activity of other muscles; can transfer mechanical power between distal and proximal joints |
| Role in Movement | Poorly understood, but can put the joint into a four-bar linkage, allowing the contraction of muscles at one joint to move the other by a fixed amount |
| Upper Body Balance | Biarticular muscles are most responsive to upper-body pitch perturbations in human standing |
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What You'll Learn
Biarticular muscles cross two joints in series
Biarticular muscles are a type of muscle that extends across two joints, while monoarticular muscles only extend across one joint. The human body contains several biarticular muscles, which are commonly found in the upper and lower extremities. These muscles generally cross two joints in series, usually in a limb, and influence movement at both. For example, the hamstrings cross both the hip and the knee, and the gastrocnemius crosses the knee and ankle joints.
The function of biarticular muscles is complex and depends on their anatomy and the activity of other muscles at the joints in question. Their role in movement is not yet fully understood. The origin (proximal attachment) and insertion (distal attachment) of a biarticular muscle can play a large role in determining its function. For instance, the gastrocnemius technically spans both the knee and ankle joints, but its origin point is so close to the axis of rotation of the knee joint that its effective lever arm would be very small compared to its large lever arm at the ankle. As a result, even though it spans two joints, it functions primarily as an ankle plantar flexor.
Biarticular muscles can also transfer mechanical power between distal and proximal joints, although the direction and magnitude of this transfer vary with anatomy, muscle activity level, and joint angles. Changes in the activity of a biarticular muscle at one joint will create torque at the other joint, and so the activity of muscles spanning the second joint must change to compensate. For example, in the propulsive phase of a jump, the thigh is extended at the coxal joint, and the shank (lower leg) is extended at the tibiofemoral joint. These joint positions cause the rectus femoris muscle to remain unchanged in net length, as the proximal and distal attachments contradict one another. By contracting isometrically (without changing length), biarticular muscles can put the joint into a four-bar linkage, allowing the contraction of muscles at one joint to move the other by a fixed amount.
Research has shown that biarticular muscles are most responsive to upper-body pitch perturbations in human standing. This suggests that biarticular muscle activity plays a strong role in restoring upper-body balance.
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They can be found in the upper and lower extremities
Biarticular muscles are those that extend across two joints, unlike monoarticular muscles, which extend across only one joint. They can be found in the upper and lower extremities of the human body, where they generally cross two joints and influence movement at both.
In the upper extremities, biarticular muscles include the brachioradialis, which is an elbow flexor muscle. In one study, a monkey generated an elbow flexor and shoulder extensor muscular torque simultaneously, and the greatest activity level was observed in the brachioradialis. This reflects the action of biarticular muscles that span both joints.
In the lower extremities, the hamstrings are biarticular muscles, crossing both the hip and the knee. Other biarticular muscles in the lower extremities include the gastrocnemius, which crosses the knee and ankle joints, and the rectus femoris, which crosses the coxal and tibiofemoral joints. The gastrocnemius and soleus muscles are collectively referred to as the triceps surae, and they provide approximately 80% of the force of PF, which is essential to nearly all forms of human locomotion.
The function of biarticular muscles is complex and depends on their anatomy and the activity of other muscles at the joints in question. Their role in movement is not yet fully understood, but they can fulfil a range of functions during movement. For example, by contracting isometrically (without changing length), they can put the joint into a four-bar linkage, allowing the contraction of muscles at one joint to move the other by a fixed amount.
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They can transfer mechanical power between distal and proximal joints
Biarticular muscles are a type of muscle that extends across two joints, unlike monoarticular muscles, which only extend across one. They are commonly found in the upper and lower extremities of the human body. Examples include the hamstrings, gastrocnemius, rectus femoris, and brachioradialis.
Biarticular muscles can transfer mechanical power between distal and proximal joints. This transfer is influenced by factors such as anatomy, muscle activity level, and joint angles. For example, the gastrocnemius acts as both a plantar flexor and a knee flexor. When the knee is flexed at a 90-degree angle, the gastrocnemius is less involved in ankle plantar flexion. This demonstrates how the position and angle of the joints can impact the transfer of mechanical power in biarticular muscles.
The ability to transfer mechanical power between joints allows biarticular muscles to play a crucial role in movement and coordination. For instance, during the propulsive phase of a jump, the rectus femoris muscle experiences a change in length due to the simultaneous extension of the thigh at the coxal joint and the lower leg at the tibiofemoral joint. By contracting isometrically (without changing length), biarticular muscles can put the joint into a four-bar linkage, enabling the contraction of muscles at one joint to move the other by a fixed amount.
The unique properties of biarticular muscles have been studied in various contexts, such as vertical jumping, gait, and upper-body balance. For example, research has shown that biarticular thigh muscles are highly involved in restoring upper-body balance during perturbations. Additionally, biarticular muscles have been found to play a role in the transfer of inter-segmental energy during propulsion, influencing the mechanical work done by the lower limb joints.
Understanding the complex functions of biarticular muscles is essential for both clinical applications and improving our knowledge of human movement and performance.
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They are most responsive to upper-body pitch perturbations in human standing
Biarticular muscles are those that cross two joints, such as the hamstrings, which cross the hip and knee joints. The function of these muscles is complex and depends on their anatomy and the activity of other muscles at the joints. The human gastrocnemius, for instance, spans the knee and ankle joints, but its origin point is so close to the axis of rotation of the knee joint that it primarily functions as an ankle plantar flexor.
The role of biarticular muscles in movement is not well understood, but they can transfer mechanical power between distal and proximal joints. They can also hold the joint at various lengths, creating a range of properties as needed. This makes them crucial in understanding an organism's movement using inverse dynamics.
Postural tone, or the tonic and dynamic regulation of the human body axis, is critical in maintaining stability during complex motor tasks and static postures. Biarticular muscles can contribute to postural stability by contracting isometrically, thereby putting the joint into a four-bar linkage and allowing the contraction of muscles at one joint to move the other by a fixed amount.
Research on postural muscle tone in healthy humans has examined the activation of neck muscles during upper limb movement and perturbations. The sternocleidomastoid (SCM) and cervical extensor (CE) muscles, for instance, demonstrated feed-forward activation during rapid arm movements in all directions. This feed-forward activation is necessary for achieving stability for the visual and vestibular systems and protecting the cervical spine.
Therefore, biarticular muscles, with their ability to transfer power between joints and maintain postural stability, are likely to be responsive to upper-body pitch perturbations in human standing. Their complex functions and ability to adapt to various joint angles and lengths make them crucial for maintaining balance and stability during perturbations.
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They can be mono- or bi-articular in the human thigh
Biarticular muscles are muscles that cross two joints, while monoarticular muscles only extend across one joint. Biarticular muscles can be found in the upper and lower extremities of the human body and are known to influence movement at both joints they cross. The function of these muscles is complex and depends on their anatomy and the activity of other muscles at the joints in question.
In the human thigh, biarticular muscles include the rectus femoris and gastrocnemius. The rectus femoris crosses the coxal and tibiofemoral joints, and its function is not immediately evident from its anatomy. The gastrocnemius crosses the knee and ankle joints, but its origin point is so close to the axis of rotation of the knee joint that it functions primarily as an ankle plantar flexor.
Monoarticular muscles in the human thigh include the deltoid posterior and deltoid anterior, which reside on the shoulder joint, and the psoas major and gluteus maximus, which reside on the hip joint.
The role of biarticular muscles in the human thigh is particularly important for restoring upper-body balance. For example, during upper-body pitch perturbations, the biarticular HAM muscle group delivers simultaneous hip extension and knee flexion torques, while the RF muscle group delivers simultaneous hip flexion and knee extension torques.
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Frequently asked questions
Biarticular muscles are muscles that cross two joints, rather than just one.
Examples of biarticular muscles include the hamstrings, gastrocnemius, rectus femoris, and brachioradialis.
The function of biarticular muscles is complex and depends on their anatomy and the activity of other muscles at the joints. They can transfer mechanical power between distal and proximal joints, and their role in movement is still not fully understood.
By contracting isometrically (without changing length), biarticular muscles can put the joint into a four-bar linkage, allowing the contraction of muscles at one joint to move the other by a fixed amount. They also influence movement at both joints they cross.
