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Muscles that cross two joints are called two-jointed muscles or biarticular muscles. They are more complex than single-joint muscles due to their dual actions. 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. These muscles have functions at each of the joints they cross, such as knee flexion and hip extension in the case of the hamstrings. Two-jointed muscles can be found in all major joints of the body, including the shoulders, elbows, hips, knees, and ankles.
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What You'll Learn
Hamstrings cross the hip and knee joints
The hamstrings are a group of three muscles—the semitendinosus, semimembranosus, and biceps femoris—that cross the hip and knee joints. These muscles are located at the back of the thigh, starting at the pelvis and extending to the knee. They are attached to the bones in the pelvis, knee, and lower leg via tendons.
The hamstrings play a crucial role in many daily activities such as walking, climbing stairs, running, jumping, and controlling some movement in the gluteus. They are involved in knee flexion (heel to buttocks) and hip extension (extending the thigh backward). The hamstrings contract when the knee is bent and lengthen when the knee is extended, and when the hips are extended.
Hamstring injuries are common in athletes who perform activities that require quick stops and starts, such as soccer, football, sprinting, and basketball. They can also occur in skiers, skaters, dancers, and other athletes who often have their knees bent in deep squat positions. Therefore, it is important to properly warm up and stretch before performing any physical activity to reduce the risk of hamstring injuries.
The hamstrings are considered typical two-jointed muscles, and they have a powerful action at both joints. At the lower insertion end, they are involved in the leg curl (knee flexion), which develops the mid to lower hamstring. At the upper end, which is attached to the pelvis, the upper hamstrings are involved in hip extension, as seen in straight-leg pulldowns.
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Gastrocnemius crosses the knee and ankle joints
The gastrocnemius is a two-headed muscle located at the back of the lower leg in humans. It is one of the two main muscles that make up the calf muscle, the other being the soleus. The gastrocnemius is a complex and powerful muscle that is fundamental for walking, running, jumping, and posture.
The gastrocnemius crosses the knee and ankle joints. It runs from the back of the knee to the heel, extending across a total of three joints: the knee, ankle, and subtalar joints. The muscle gets its name from the Latin, derived from the Greek γαστήρ (gaster), meaning 'belly' or 'stomach', and κνήμη (knḗmē), meaning 'leg'. Thus, its name can be translated as 'stomach of the leg', referring to the bulging shape of the calf.
The gastrocnemius originates on the condyles of the femur, with its two heads located on the medial and lateral condyles. It then extends down the back of the leg and attaches to the Achilles tendon, which inserts onto the heel bone or calcaneus. The gastrocnemius, along with the soleus, helps to flex the foot and support the legs, enabling activities such as walking, running, and jumping.
The gastrocnemius is a biarticular muscle, which means it crosses two joints. This gives it a more complex function compared to single-joint muscles. While the gastrocnemius technically spans both the knee and ankle joints, its primary function is as an ankle plantar flexor. This is because the origin point of the muscle is close to the axis of rotation of the knee joint, resulting in a small lever arm at the knee and a larger lever arm at the ankle.
Injuries to the gastrocnemius muscle, such as strains or inflammation, are common due to its connection to two joints. A severe ankle dorsiflexion force may result in a Medial Gastrocnemius Strain (MGS) injury, commonly known as a "torn" or "strained" calf muscle, which can be extremely painful and disabling.
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Rectus femoris crosses the hip and knee joints
The rectus femoris is a muscle that crosses the hip and knee joints. It is part of the quadriceps group and is the only muscle in the group that crosses the hip joint. It is located in the middle of the front of the thigh and is the most superficial and vertically oriented muscle in the group. The rectus femoris is also known as the "kicking muscle" because of its role in forceful knee extension.
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 indirect head originates from the superior acetabular ridge. The muscle flexes the hip and extends the knee. It works with the iliopsoas to produce hip flexion, especially when the knee is flexed. During gait, as a hip flexor, it acts with the iliopsoas in the "toe off" phase.
The rectus femoris is a weaker hip flexor when the knee is extended because it is already shortened and suffers from active insufficiency. Similarly, it is less dominant in knee extension when the hip is flexed as it is shortened and experiences active insufficiency. The muscle's ability to flex the hip and extend the knee can be compromised in a position of full hip extension and knee flexion due to passive insufficiency.
The rectus femoris is prone to injury because it crosses two joints. Rectus femoris strain, also known as hip flexor strain, is a common injury at the tendon that attaches to the patella or in the muscle itself. The injury is often caused by forceful movements related to sprinting, jumping, or kicking and is frequently seen in sports such as football and soccer. Symptoms of a rectus femoris strain include sharp pain at the front of the hip or groin, swelling, bruising, and an inability to contract the muscle with a full tear.
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Single-joint muscles vs two-joint muscles
Single-joint muscles and two-joint muscles differ in their functions and the types of exercises that target them. Single-joint muscles, also known as isolation muscles, are involved in the movement of only one joint. For example, when performing a bicep curl, only the elbow joint moves, specifically recruiting and activating the bicep muscle. Single-joint exercises are beneficial due to their reduced technical and coordinative demands. They are also better suited for targeting specific muscles and correcting imbalances between muscle groups.
On the other hand, two-joint muscles, or biarticular muscles, cross two joints, usually in a limb, and have more complex functions. For instance, the hamstrings cross both the hip and knee joints. The function of two-joint muscles 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, with the direction and magnitude of the transfer varying with anatomy, muscle activity level, and joint angles.
Multi-joint exercises, which target two-joint muscles, have traditionally been viewed as more effective than single-joint exercises for increasing maximal strength, muscle activation, and metabolic stress. They also more closely mimic daily tasks and sports-specific movement patterns. However, recent studies suggest that single-joint exercises can also induce similar strength increases. Therefore, a combination of both single-joint and multi-joint exercises can be beneficial for overall strength development and targeting specific muscle groups.
Examples of single-joint exercises include bicep curls, hamstring curls, and triceps extensions. Multi-joint exercises include squats, deadlifts, and bench presses, which involve the movement of multiple joints and muscle groups.
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Active and passive insufficiency
Multi-joint muscles, also known as two-joint muscles, cross two joints and have an action at each of the joints. Examples include the hamstrings, which cross the knee and hip joints, the rectus femoris, which crosses the hip and knee joints, and the gastrocnemius, which crosses the knee joint and flexes the ankle.
Multi-joint muscles are more complex in their functions and are not as powerful as single-joint muscles. They also exert tension in an oblique manner. This complexity can be observed when considering active and passive insufficiency, which are important concepts in exercise prescription, fitness training, and post-injury recovery.
Active insufficiency occurs when a multi-joint muscle shortens over two joints simultaneously, resulting in a loss of muscle tension and limiting the full range of motion at one of the joints. This happens because the muscle cannot contract strongly over all the joints at the same time. For example, active insufficiency in the hamstrings during knee flexion can be addressed through rehabilitation exercises that isolate and stretch the hamstrings while allowing knee flexion, such as seated or lying hamstring stretches with the knee flexed.
Passive insufficiency, on the other hand, is the opposite of active insufficiency. It occurs when a multi-joint muscle is stretched to its maximum length at both joints but restricts the full range of motion of each joint it crosses. This limitation is normal for multi-joint muscles and helps optimize the relationship between muscle length and tension. For instance, passive insufficiency in the quadriceps can be mitigated through rehabilitation exercises that involve gradual knee flexion while avoiding simultaneous hip extension.
Understanding active and passive insufficiency is crucial for designing targeted rehabilitation strategies and tailoring exercises to specific muscles and joints during recovery.
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Frequently asked questions
A two-jointed muscle, also known as a biarticular muscle, crosses two joints and has an action at each of the joints. This makes the function of these muscles more complex than single-joint muscles.
Examples of two-jointed muscles include the hamstrings, rectus femoris, gastrocnemius, and biceps.
Two-jointed muscles can produce movement at more than one joint, which is advantageous for many human movements.
Two-jointed muscles can become inefficient when trying to exert full active or passive motion at both joints simultaneously. This results in reduced composite force at the joints, a condition known as active or passive insufficiency.
