Angular stiffness in the knee during FES and iso-velocity movement in a paraplegic

Using a torque motor to impose iso-velocity movement in the knee of a paraplegic patient, the angular stiffness was measured while applying functional electrical stimulation (FES) to the knee extensor muscles. During both knee extension and flexion the stiffness increased when the amplitude of FES increased. However, faster knee flexion increased stiffness, while faster knee extension caused a decrease in stiffness when the FES amplitude was high.