Dominic Stone
Biarticular muscles are those that cross two joints, such as the hamstrings, which cross both the hip and the knee. The function of these muscles is complex and depends on their anatomy and the activity of other muscles at the joints. Biarticular muscles are most responsive to upper-body pitch perturbations in human standing and play an important role in transferring power from proximal to distal joints. Recent studies suggest that different regions within biarticular muscles may have different actions. For example, the rectus femoris contracts in the thigh, flexing the hip joint and extending the knee joint.
| Characteristics | Values |
|---|---|
| Definition | Muscles that cross two joints, rather than just one |
| Examples | Hamstrings, Rectus femoris, Gastrocnemius, Biceps femoris long head |
| Function | Complex and varied, depending on anatomy and activity of other muscles |
| Role in Movement | Not well understood, but can transfer mechanical power between joints |
| Unique Role | Control distribution of net moments about hip and knee joints |
| Stabilisation | Help stabilise the trunk during walking and generate leg swing motions |
| Upper Body Balance | Respond strongly to upper-body pitch perturbations in standing positions |
| Running | May function similarly to tendons, maintaining tone without changing length |
| Strength | Acquire strength by resisting forces applied during running |
| Training | Training with specific use of biarticular musculature can improve running ability |
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What You'll Learn
Biarticular muscles cross two joints
The rectus femoris (RF) is another example of a biarticular muscle that spans the hip and knee joints. It is an extensor of the leg. The RF is also known to play a significant role in hip flexion, which can be a challenge when considering quadriceps strengthening regimens. The RF is one of the postural muscles that tend to tighten, and increasing its strength may lead to a muscle imbalance.
Biarticular muscles have traditionally been thought to behave as single actuators, but recent studies suggest that different regions within these muscles may have distinct functions. For instance, the cat biceps femoris muscle, which crosses the knee and hip joints, has a caudal portion that contributes to knee flexion, while its rostral part aids in hip extension during locomotion.
These muscles are also important in maintaining balance and controlling the direction of the Ground Reaction Force (GRF) during walking or running. They are highly responsive to upper-body pitch perturbations, helping to stabilise the trunk and generate appropriate leg swing motions.
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They can be found in the thigh, hindlimbs, forelimbs, and arms
Biarticular muscles are those that cross two joints, usually in a limb. They can be found in the thigh, hindlimbs, forelimbs, and arms.
In the thigh, biarticular muscles include the rectus femoris and the biceps femoris long head. When the rectus femoris contracts, it flexes the hip joint but extends the knee joint. The biceps femoris long head has the opposite effect, extending the hip joint and flexing the knee joint.
In the hindlimbs, biarticular muscles include the triceps brachii long head and the biceps brachii long head, which cross between the shoulder and elbow joints.
In the forelimbs, the rectus femoris and biceps femoris long head are also considered biarticular muscles, as they cross between the hip and knee joints.
Biarticular muscles in the arms include the triceps brachii long head and the biceps brachii long head, which cross the shoulder and elbow joints.
The function of biarticular muscles is complex and depends on their anatomy and the activity of other muscles at the joints. They can play a role in postural control and balancing the upper body, especially during walking and running.
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Examples include the hamstrings, gastrocnemius, and rectus femoris
Biarticular muscles are muscles that cross two joints, rather than just one. They can hold a joint at many different lengths, creating a range of four-bar properties as needed. They can also transfer mechanical power between distal and proximal joints, though the direction and magnitude of transfer vary with anatomy, muscle activity level, and joint angles.
The hamstrings are biarticular muscles, crossing both the hip and the knee. The role of biarticular muscles like the hamstrings is a topic that has received considerable attention, but their function is not well understood.
The gastrocnemius is also a biarticular muscle. It 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 at the knee is very small. As a result, it functions primarily as an ankle plantar flexor.
The rectus femoris is another example of a biarticular muscle. It is the only muscle in the quadriceps group that crosses the hip. It crosses over the hip and knee joints, functioning to extend the knee and assist the iliopsoas in hip flexion.
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They can transfer mechanical power between distal and proximal joints
Biarticular muscles are muscles that cross two joints, usually in a limb. Examples include the hamstrings, which cross the hip and knee joints, and the rectus femoris, which crosses the hip and knee joints. The gastrocnemius technically spans 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.
Biarticular muscles can transfer mechanical power between distal and proximal joints. This transfer of power is crucial when analyzing an organism's movement using inverse dynamics. The direction and magnitude of the transfer depend on anatomy, muscle activity level, and joint angles.
During the propulsive phase of a jump, the thigh is extended at the coxal joint, and the lower leg is extended at the tibiofemoral joint. In this case, the rectus femoris muscle remains unchanged in net length because the proximal (eccentric action) and distal (concentric action) attachments are contradicting one another. By contracting isometrically (without changing length), biarticular muscles put the joint into a four-bar linkage, allowing the contraction of muscles at one joint to move the other by a fixed amount.
During a squat vertical jump and in the push-off phase during running, the rectus femoris and gastrocnemius transfer mechanical energy from the proximal joints of the leg to the distal ones. At landing and in the shock-absorbing phase during running, the two-joint muscles transfer energy from the distal to proximal joints.
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Their function is not well understood
Biarticular muscles are those that cross two joints, usually in a limb, as opposed to monoarticular muscles, which cross only one. Examples of biarticular muscles include the hamstrings, which cross the hip and knee joints, and the gastrocnemius, which 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 well understood, and their specific functions have spurred the interest of researchers for centuries. While biarticular muscles have traditionally been considered to behave as single actuators, this is now being questioned. Recent studies suggest that different regions within biarticular muscles may have different actions. For example, animal studies have demonstrated that different regions of the cat biceps femoris muscle, which crosses the knee and hip joints, contribute to different joint actions. Similarly, human cadaveric studies have assumed a heterogeneous functional organization within some biarticular muscles, based on their anatomical properties.
Biarticular muscles can contract isometrically (without changing length), putting the joint into a four-bar linkage, which allows 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 vary with anatomy, muscle activity level, and joint angles. This transfer of power from proximal to distal joints has been supported by studies using high-density surface electromyography and intramuscular electromyograms.
Biarticular muscles are believed to play an important role in efficient and robust locomotion, particularly in postural upper-body control in standing and potentially in upper-body balance in walking. They are most responsive to upper-body pitch perturbations in human standing, and simulations and robotic demonstrators have revealed their potential to stabilize the trunk during walking and generate appropriate leg swing motions. However, experimental evidence for the actual use of biarticular muscles for upper-body balance in humans is still missing. Further perturbation experiments are needed to target their role in upper-body balance in walking.
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Frequently asked questions
Biarticular muscles are those that cross two joints, usually in a limb, instead of just one. Examples include the hamstrings, gastrocnemius, rectus femoris, and biceps femoris long head.
The function of biarticular muscles is complex and depends on their anatomy and the activity of other muscles at the joints in question. They can transfer mechanical power between distal and proximal joints, and they can also control the distribution of net moments about the joints they span.
Lombard's paradox refers to the condition where the activation of biarticular muscles contributes to the production of torque in the opposite direction when a torque demand is imposed on either of the two joints they span.
In natural running, biarticular leg muscles do not generate movement. Instead, they acquire strength by resisting the forces applied to them during running. They can also work like tendons in some movements, maintaining tone without changing length.
