multijoint

Multijoint describes any system, mechanism, or biological structure that involves more than a single joint. In engineering and biomechanics, the term is used to emphasize the presence of multiple joints that permit complex motion, greater reach, or distributed load across a chain of segments. Multijoint configurations are common in robotic manipulators, human and animal musculature, prosthetics, and animated characters. They enable rich, coordinated movements but introduce control and mechanical challenges, such as kinematic redundancy, singular configurations, and higher sensitivity to parameter variation.

In robotics, multijoint manipulators consist of links connected by rotary or prismatic joints, forming a kinematic chain with two or more joints. They offer multiple degrees of freedom, enabling tasks that require orientation and position control in three-dimensional space. Control relies on forward and inverse kinematics, trajectory generation, and often redundancy resolution when more joints exist than strictly required for a task. Mechanical design must manage backlash, joints friction, and payload while avoiding singularities where movement is limited.

In biomechanics, multijoint or polyarticular muscles span more than one joint, such as the biceps brachii across the shoulder and elbow, or the gastrocnemius across the knee and ankle. These muscles coordinate to produce efficient movements, regulate joint torques, and stabilize joints under load. Neuromuscular control for multijoint muscles is more complex due to inter-joint coupling and concomitant joint angles.

Applications include robotic arms in manufacturing, assistive devices and prosthetics, sports science, and computer animation. Design considerations include choosing joint types, actuator placement, control algorithms, energy efficiency, and the management of kinematic redundancy to achieve smooth, reliable motion.