the continuous passive motion exercise system enables human &# 39 ; s joints to recover speedily to original functioning after injuries or surgeries , and thus shortens the period of time needed for joint rehabilitation . the present invention provides a force or torque monitoring device attached onto a continuous passive motion exercise mechanism to measure the driving force of the repeated joint flexing and extending motion , so as to evaluate the change of the viscosity and the stiffness of the injured joints through different rehabilitation periods . this monitoring device also monitor degrees of joint muscle &# 39 ; s active contraction and thus slows down or stops the repeated motions of exercise mechanisms to improve safety concerns . in addition , such a monitoring device also includes a data transceiver interface utilized for transmitting and receiving the information regarding a patient &# 39 ; s states of using such a exercise system in order to assess the patient and to provide doctors with the basis for evaluating and improving the rehabilitation condition of the injured joints .