biarticular

Biarticular refers to a structure that crosses two joints and can influence movement at both. In human anatomy, biarticular muscles span two joints, allowing coordinated action and efficient transfer of energy between joints. By contrast, uniarticular muscles cross a single joint, and multiarticular muscles cross more than two joints. Biarticular muscles may act as prime movers, stabilizers, or modulators during locomotion and posture, and they often rely on tendon elasticity to coordinate joint contributions.

Common biarticular muscles include the hamstrings (biceps femoris, semitendinosus, semimembranosus), which cross the hip and knee; the gastrocnemius, which crosses the knee and ankle; the rectus femoris, which crosses the hip and knee; and the sartorius and gracilis, which span the hip and knee as well. These muscles can produce hip extension and knee flexion, or knee flexion and ankle plantarflexion, depending on the joint angles. Because they span two joints, their length changes are coupled, requiring precise neural control to prevent joint slack or over-tension.

In biomechanics and physiology, biarticular muscles can store elastic energy and transfer power between joints during gait and jumping, improving movement efficiency. In clinical contexts, injuries to biarticular muscles may disrupt coordination across joints and require rehabilitation that addresses multi-joint function. In engineering and robotics, biarticular actuators are explored to emulate human efficiency and to simplify control of multi-joint limbs.