This paper deals with biomechanics of the iliotibial tract, which is a large ligament specific to man. First, we analysed the force equilibrium of the femur, studied the way the change of the tract in tension is compensated by the forces of joints and muscles concerned. Then, we made two kinds of photoelastic model experiments: one for investigating the change of marginal stresses in the femur as functions of parameters, e. g. tension of the tract and inclination of the knee joint; the other for confirming Pauwels' experiment.
The results show that the iliotibial tract does not have such a great deal of stress-reducing effect on the femur as has been long believed by many investigators since Pauwels indicated it in 1948. Instead of the conventional interpretation, we proposed a hypothesis that the iliotibial tract may have had an evolutionary significance in the development of human bipedal locomotion.