Moment-angle relationship at lower limb joints during human walking at different velocities.

The coupling between joint kinematics and kinetics during level walking was analysed by plotting joint angles vs. joint moments about the hip, knee and ankle in nine normal male subjects walking at three different velocities. The curves obtained were reproducible, and variability among subjects was relatively low. Counterclockwise loops corresponded to energy produced, and clockwise loops to energy absorbed at the joint; both loops are described in different phases of the stride cycle. At increasing walking velocity some of the loops narrowed, thus revealing the possibility of energy recovery. Analysis of individual diagrams revealed that consistent portions of the moment-angle loops can be described as a sequence of quasi-constant slope phases, separated by transition periods where quasi-isometric changes in joint moment occur. This figure, which was particularly evident of the hip and ankle joints, is reminiscent of a mechanical system with elastic components, which, in different phases of the rhythmic locomotion activity, moves along discrete status levels characterized by specific length-tension relationships. Implications of the above results in terms of the neurol control of joint properties during active movement are discussed.