Figure 8

Schematic representation of the leg, modeled as a rigid body. L is the distance from the center of the knee joint to either the center of the calf pad of the Biodex dynamometer knee attachment or the center of the load applied just proximal to the ankle when the leg is not attached to the dynamometer (just proximal to the malleoli but distal to the prominent calf musculature), l is the distance from the center of the knee joint to the center of mass of the tibia, T _stim is the torque at the knee due to stimulation, F _ext is the either the force measured by the Biodex dynamometer (F _Bio ) if the leg is attached to the dynamometer (the resistance that the force dynamometer exerts against the ankle to maintain a constant angular velocity) or the component of the applied ankle weight (F _load ) that resists the contractile force of the quadriceps if the leg is swinging free, mg is the weight of the leg below the knee and the foot, and H is the resistance moment to knee extension due to the visco-elasticity of the structures at the knee.