Stiffness control for lower leg muscles in directing external forces

The role of lower leg muscles is investigated during contact control tasks, in which the external force, applied by the foot on the surface, has to be controlled. Force, position and muscle activation were recorded. All subjects showed a stereotyped activation pattern to accomplish the tasks. The torques about hip and knee changed by a reciprocal activation pattern of the upper leg muscles, whereas the ankle torque remained remarkably constant as a result of a strong co-activation of the ankle muscles.