The study and correction of human gait by electrical stimulation

To gain a better understanding of the functions that the calf and vastus muscles perform in the human walking gait the author systematically increased the contractions of these muscles separately and in combination by applying Functional Electrical Stimulation (FES) to them, during walking tests performed by a subject with nonpathological gait, and a patient with a hemiplegic gait. A four-channel stimulator was used with foot switch activated control systems, which accurately sequenced the FES pulses and timed them in relation to the footswitch contacts. In normal gait FES applied to the calf muscles in the first third of the stance phase induced knee extension, but when applied later in the stance phase it increased the amount of plantar flexion and knee flexion at the push off. Strengthened vastus muscle contraction increased the amount and duration of stance phase knee extension, and interacted with the calf FES to increase the amount of heel rise at the push off. In the hemiplegic gait calf FES resulted in some increased knee flexion and ankle plantar flexion after the opposite heel strike, but a persistent lower limb extensor synergy prevented knee flexion from occurring simultaneously with plantar flexion and a heel rise, while the hemiplegic limb was still weight bearing.