Unstable states in four-point walking.

The presently utilized walking patterns in paraplegic subjects with complete spinal cord injury (SCI) are compared by the help of graphic representations. Improved four-point gait assisted by functional electrical stimulation (FES) and crutches is proposed by introducing unstable states into the walking sequence. The unstable states are defined as passive phases of walking where the centre of mass (COM) is gravity driven in the direction of progression. The unstable state is described by a simple inverted pendulum model. Kinematic measurements of the unstable state were performed in normal and paraplegic subjects.