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Biarticular muscles, or two-joint muscles, are those that cross two joints in the body, such as the hamstrings, which cross the hip and knee joints. They are structured to perform more than one joint function, such as lifting and extending the leg. These muscles can be found in the upper and lower extremities of the human body and are important for efficient movement, as they require less energy to move two joints than recruiting two separate muscles.
| Characteristics | Values |
|---|---|
| Name | Biarticular muscles, Biarticulated Muscles, 2JMs |
| Definition | Muscles that cross two joints in series, usually in a limb |
| Examples | Hamstrings, Rectus Femoris, Gastrocnemius, Triceps Brachii Long Head, Biceps Brachii Long Head |
| Function | Transferring energy, ease of control, muscle bulk reduction, decreased velocity of contraction |
| Role in Movement | Complex and not well understood; can contract isometrically, allowing contraction of muscles at one joint to move another by a fixed amount |
| Advantages | Efficiency of movement, less energy required, useful for strength and speed movements |
| Disadvantages | Active and passive insufficiency, reduced composite force at the joints |
| Applications | Running, jumping, climbing, sports and exercise, rehabilitation |
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What You'll Learn
Hamstrings cross the hip and knee joints
The hamstrings are a group of three muscles that cross the hip and knee joints. They are skeletal muscles located at the back of the thigh, starting at the pelvis and extending to the knee. They are called the biceps femoris, semitendinosus, and semimembranosus.
The hamstrings have a variety of functions, including flexing the knee joint and extending the hip, which enables essential lower limb activities such as walking, running, and climbing. They also have an important stabilizing function. For example, when a person tilts forward, the hamstrings activate and counteract the tilting movement to stabilize the hip joint and prevent falling.
The biceps femoris is a two-headed muscle that runs through the posterior thigh. It flexes the knee, extends the thigh at the hip, and rotates the lower leg from side to side when the knee is bent. The semitendinosus and semimembranosus muscles have similar functions, with the semimembranosus also rotating the hip and lower leg.
Hamstring injuries are common in athletes who perform quick stops and starts or run at fast speeds, such as sprinters and soccer players. These injuries can be prevented by proper warm-ups, stretching, and resting the muscles when pain or fatigue is felt.
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Rectus femoris crosses the hip and knee joints
The rectus femoris is a muscle in the quadriceps group that crosses the hip and knee joints. It is the only muscle in the quadriceps group that crosses the hip joint. It is the most superficial and vertically oriented muscle in the anterior thigh compartment. The rectus femoris is also known as the "kicking muscle" because it is involved in activities that require forceful knee extension. It is the quadriceps muscle most prone to injury due to its length and the fact that it spans two joints.
The rectus femoris has two origins: the direct head and the indirect head. The direct head originates from the anterior inferior iliac spine, while the superior acetabular ridge is the origin of the indirect head. The rectus femoris functions in both hip flexion and knee extension. It acts with the 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.
The rectus femoris is involved in forceful knee extension, which is required for activities such as kicking a soccer ball. It is one of the postural muscles that tend to tighten, which can lead to muscle imbalance and LCS. Acute rectus femoris strain can result in swelling and moderate to severe pain in the groin or anterior aspect of the hip, with impaired knee extension.
The rectus femoris is a biarticular muscle, which means it crosses two joints in series, usually in a limb. The function of biarticular muscles is complex and depends on both their anatomy and the activity of other muscles at the joints. The rectus femoris can be distinguished from the other quadriceps muscles by its nearly vertical orientation, superficial location, and crossing of two lower limb joints.
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Gastrocnemius crosses the knee and ankle joints
The gastrocnemius is a complex muscle that is fundamental for walking, posture, and running. It is a biarticular muscle, meaning it crosses two joints in series, usually in a limb. In this case, the gastrocnemius crosses the knee and ankle joints.
The gastrocnemius forms the major bulk at the back of the lower leg and is a very powerful muscle. It has two heads, which are located on the medial and lateral condyles of the femur, and runs from the back of the knee to the heel. The two heads come together and insert into the posterior surface of a broad membranous tendon, which then fuses with the soleus tendon to form the upper part of the tendocalcaneus. The gastrocnemius, along with the soleus and plantaris, forms a composite muscle called the triceps surae.
The gastrocnemius is the main plantar flexor of the ankle joint and a secondary knee flexor. It provides a significant amount of propulsive force when running, walking, or jumping. The muscle tension in the gastrocnemius has many fascial connections, and this tension is transmitted not only to the foot but also to the knee, hip, and lumbar area.
To achieve an effective gastrocnemius stretch, the knee must be in extension while the ankle is dorsiflexed. This can be done through exercises such as long-sitting or with the knees partially flexed. By manipulating the angles of both joints, the actions of the gastrocnemius can be influenced, as joint angles play a dynamic role in determining muscle function.
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Muscles that cross two joints are called biarticular muscles
The function of biarticular muscles is complex and depends on their anatomy and the activity of other muscles at the joints they cross. Their role in movement is not well understood, but they can perform a range of functions. For example, they can contract isometrically (without changing length) to put the joint into a four-bar linkage, allowing the contraction of muscles at one joint to move the other by a fixed amount.
Biarticular muscles can also transfer mechanical power between distal and proximal joints, but the direction and magnitude of this transfer depend on anatomy, muscle activity level, and joint angles. This is important to consider when analyzing an organism's movement using inverse dynamics.
The actions of biarticular muscles are influenced by joint moment arms and muscle length, which are dynamic factors that change as joint angles are altered. Therefore, to fully understand the actions of these muscles, the angles of both joints they cross must be manipulated.
Biarticular muscles may also play a key role in dealing with typical perturbations (e.g. pushing, stumbling, or walking on uneven ground) by coordinating multiple joints. They contribute strongly to the leg force that acts perpendicular to the leg axis, making them particularly useful for postural control.
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Active and passive insufficiency are limitations of biarticular muscles
Biarticular muscles cross two joints in series, usually in a limb. Examples of biarticular muscles include the hamstrings, which cross both the hip and the knee, and the gastrocnemius, which crosses the knee and ankle.
The function of these 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.
One important concept of biarticular muscles is the change in muscle length when motion occurs at the proximal and distal ends of the muscle. For example, during a jump, the thigh is extended at the coxal joint, and the shank (lower leg) is extended at the tibiofemoral joint. These joint positions can cause the muscle to remain unchanged in net length, as the proximal and distal attachments contradict one another.
Biarticular muscles can contract isometrically (without changing length) and 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 can also transfer mechanical power between distal and proximal joints, though the direction and magnitude of this transfer vary with anatomy, muscle activity level, and joint angles.
Active insufficiency occurs in a biarticular muscle when it cannot shorten enough to cause a full range of motion in both of the joints it crosses at the same time. For example, active insufficiency in the hamstrings can restrict full hip flexion due to shortening. Another example is the gastrocnemius, which can experience active insufficiency during ankle extension and knee flexion.
Passive insufficiency, on the other hand, occurs when a biarticular muscle cannot be stretched enough to permit a full range of motion at both joints simultaneously. For instance, passive insufficiency in the hamstrings can prevent full knee flexion and full hip extension at the same time due to the muscle being lengthened to its fullest extent at both joints. Similarly, the rectus femoris can experience passive insufficiency, limiting full knee flexion if the hip is fully extended.
These limitations are normal properties of multijoint muscles and help optimize the relationship between muscle length and tension. Understanding active and passive insufficiency is crucial for designing targeted rehabilitation exercises to improve or maintain the range of motion at specific joints.
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Frequently asked questions
Biarticular muscles, or 2JMs, are muscles that cross two joints in the body and are structured to perform more than one joint function.
Examples of biarticular muscles include the hamstrings, rectus femoris, gastrocnemius, and triceps brachii long head.
Biarticular muscles have various functions, including transferring energy, ease of control, muscle bulk reduction, and decreased velocity of contraction. They also play a role in transferring mechanical power between distal and proximal joints.
Biarticular muscles influence movement by creating efficiency. Less energy is required to move two joints with a single muscle compared to using two separate muscles. This makes them useful for strength and speed movements like running and jumping.
Biarticular muscles have limitations such as active and passive insufficiency. Active insufficiency occurs when a biarticular muscle reaches a shortened length and can no longer exert an effective force. Passive insufficiency happens when the muscle is lengthened to its fullest extent, preventing the full range of motion at each joint.
