jointposition

Joint position refers to the orientation or angle of a joint at a given moment, relative to a defined reference posture, usually the anatomical neutral position. In human anatomy, joints have specific planes and degrees of freedom, and joint position is commonly described by joint angles such as flexion, extension, abduction, adduction, and rotation. The concept is central to biomechanics, rehabilitation, and animation, where precise knowledge of joint position enables the analysis of movement and the reproduction of pose.

Joint position can be measured directly with physical tools such as a goniometer or electrogoniometer, or indirectly via motion capture systems, optical tracking, or inertial measurement units. In measurements, the joint angle is defined with respect to anatomical reference axes and may be expressed in degrees or radians. In robotics and control engineering, joint position is a state variable that represents the angular or linear displacement of a joint, captured by encoders, potentiometers, or resolver sensors. These sensors feed control loops to achieve specified positions.

Representative ranges vary by joint: the knee typically flexes from 0 to about 130–135 degrees; the elbow from 0 to about 140–150 degrees; the hip from 0 to about 120 degrees. Neutral or zero position is not universal; it depends on the chosen reference frame. Joint position alone does not convey force, torque, or contact conditions, which must be considered for a complete movement analysis.

Applications include clinical assessment and rehabilitation planning, ergonomic design, sports science, animation and virtual reality, and robotic manipulation, where accurate joint position data supports movement analysis, pose estimation, and control.