An experimental and analytic study of the dynamic properties of the human leg

Certain problems in the dynamics of the human body are characterized by large displacements of the parts of the body compared to the deformations of the tissues themselves. In such problems, it is convenient to think of the human body as a chain of rigid links, representing the anatomical segments, with joints between the rigid links representing the articulations of the human body.

Skeletal muscles are capable of creating torques at the joints of the body. The joint torques of the rigid link model should portray the static strength of skeletal muscle, the degradation of muscle strength with rate of shortening, the feedback control of the stretch reflex, and the viscoelastic properties of the muscles, tendons, and joint capsules.

In this study a sinusoidal test is performed upon the knee joints of nine subjects. The increment of knee moment required to flex and extend the knee slightly for various conditions of knee angle, knee angular velocity, and steady knee moment is measured. The hip angle is maintained constant. After the effects of leg inertia are removed, the resulting data are shown to obey a Maxwell fluid model in which the model coefficients depend upon the absolute value of the knee moment.