A mathematical model of the swing phase of walking is presented in this paper. The body is represented by three links, one for the stance leg and two for the thigh and shank of the swing leg. It is assumed that the muscles act only to establish an initial configuration and velocity of the limbs at the beginning of the swing phase. The swing leg and the rest of the body then moves through the remainder of the swing phase entirely under the action of gravity.

The range of possible times of swing for each step length is computed for two types of gaits;​ stiff-legged walking and walking with flexion at the knee. The range of times of swing found for the model with flexion at the knee are compared with published experimental results. The agreement is shown to be very close. Typical histograms of forces applied to the ground and angles of the limbs against time are also given. The computed forces and angles have the same general time course as those found experimentally in normal walking, with the exception of the vertical force, which often has a different shape. The limitations of the model apparently responsible for this discrepancy are discussed.