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In-vivo muscle length-force-joint angle relationship for quasi-static muscle action of the biceps muscle

Experimental findings of non invasive in-vivo monitoring are essential to study the diversity and evolution of musculoskeletal kinematics. In this paper, results obtained from the uni-axial monitoring of the quasi-static dynamics of the biceps muscle-belly are reported. Monitoring of the belly diameter is based on a custom developed ultrasonic caliper combined with the synchronously recorded applied external force and joint angle variations detected with a custom build ultrasonic force sensor and a resistive angle decoder respectively. The monitored muscle action includes the processes of active muscle contraction and relaxation in a closed path starting with an initial isotonic contraction followed by eccentric (spring like) stretching. The technology applied here allows for observations of those processes and registration of their paths in the length-forceangle parameter space. That way of presentation reveals that at some conditions the closed-loop human cycles follow in close approximation characteristic lines of well identifiable elementary processes. The presentation of these processes in the length-force parameters space allows for discussion of the mechanical energy expenditure during different muscle actions. Comparative studies of identical closed-loop muscle actions and the joint angle-force-length relationships of the muscle-tendon complex are presented. This synchronous monitoring also allows quantifying the joint torques and positions with high accuracy for living person.