Introduction. The number of arthroscopic reconstructions of the anterior cruciate ligament (ACL) has been increasing not only among competitive athletes, but also among recreational athletes. The monitoring of the rehabilitation process in order to determine a safe time to return to the pre-injury activity is thus of great practical importance. The aim of this paper is to analyse the changes in selected biomechanical variables which occur after the therapeutic training following an anterior cruciate ligament reconstruction. Materials and methods. Twenty nine males (age 27.3 ± 5.7 years) after the anterior cruciate ligament reconstruction participated in the study. A quadruple-stranded semitendinosus/gracilis graft was used for the reconstruction. The biomechanical evaluation of the rehabilitation process was provided by an isokinetic dynamometer Biodex System Pro-3 working at speeds of 60 deg/s and 180 deg/s during testing the knee extensor and flexor muscles. In the case of an injured limb, the absolute peak torque, relative peak torque, average power and hamstring/ quadriceps (H/Q) ratio were determined. In addition, the values of flexor and extensor torques for healthy and injured limbs were compared. The study was carried out in four stages: before the surgery, three, six and twelve months after the surgery. Results and analyses. The results showed significant differences in each value between various stages of the biomechanical rehabilitation process of the knee. The applied therapeutic training influenced significantly the changes in the values of the tested variables. The results have confirmed that the biomechanical measurements can be treated as a supplementation to the clinical evaluation of the patient after ACL reconstruction. They may also be used for the optimisation of the therapeutic training.