Tension development and muscle activation in the leg during gait in spastic hemiparesis: independence of muscle hypertonia and exaggerated stretch reflexes.

In 15 patients with spastic hemiparesis the development of tension of calf muscles in relation to their electrical activation and their stretching period was studied on both sides during locomotion. Only in the spastic leg did isolated small biphasic potentials appear in the gastrocnemius E.M.G. with monosynaptic latency at the beginning of the stance phase, while the remaining gastrocnemius activation was reduced compared to the unaffected side. Perturbations of gait were followed in the spastic leg by a large monosynaptic response, while the polysynaptic reflex response was reduced. In the unaffected leg only a strong polysynaptic response appeared, which suggests a reciprocal modulation of monosynaptic and polysynaptic reflex responses. Tension development paralleled the gastrocnemius E.M.G. in the unaffected leg, while in the spastic leg tension was more closely correlated to muscle stretch. It is concluded that in spasticity the exaggerated monosynaptic reflexes represent only a small part of leg extensor activation during gait and that the tension development does not depend on these reflexes.