Voluntary and reflexive muscle activation of human elbow joint is investigated by both subject tests and numerical simulations. A jerk loading is applied to extend the elbow joint with different muscle tensing and pre-recognition conditions. Interand Intra-subject variations of hand displacement are analyzed for an objective assessment of the active response at the elbow joint to the external perturbation. Both Modelica and finite element mesh models are developed using passive kinematic joint element and active torque which has PID close loop control. The simulation result from these two models are compared with test results and shows a good correlation.