Aim of the work was the experimental validation of musculoskeletal models of lower limbs during isokinetic knee flexion-extensions at different angular speeds, using OpenSim® and AnyBody® codes. The adopted approach was: (i) to record the kinematic, kinetic and EMG data on two healthy subjects, (ii) to implement the scaled numerical models of the two subjects within the two codes, (iii) to simulate the isokinetic motions of each subject in each code and (iv) to compare the numerical and experimental activation results in terms of peak, phase and area errors. Results showed a good agreement for extensor muscles, giving an encouraging confirmation about the possibility of using such codes for the evaluation of joint loads.