REFLEX STIFFNESS OF MANS ANTI-GRAVITY MUSCLES DURING KNEEBENDS WHILE CARRYING EXTRA WEIGHTS

The effective lumped stiffness and damping ratio of the human leg system was determined from measurements of parallel and antiparallel-mode oscillations while standing on a linear spring. Knee flexion angle was held fixed in each trial, and varied systematically from 0° to 75°. At each knee angle, subjects carried weights up to twice body weight on their shoulders to determine the effect of increasing muscle force. For small knee flexion angles (θ ≤ 30°), reflex stiffness was independent of muscle force, but rose slightly with muscle force for large flexions. The damping ratio was calculated to be 0.34, showing the underdamped character often reported for skeletomotor feflex mechanisms. Leg stiffness measured in this way is consistent with measurements taken during human running. © 1979.