Flexor reflexes in chronic spinal cord injury triggered by imposed ankle rotation.
Hypersensitivity of the flexor reflexes to input from force-sensitive muscle afferents may contribute to the prevalence and severity of muscle spasms in patients with spinal cord injuries. In the present study, we triggered flexor reflexes with constant-velocity ankle movements into end-range dorsiflexion and plantarflexion positions in 8 individuals with spinal cord injuries. We found that all 8 subjects had coordinated increases in flexion torque at the hip and ankle following externally imposed plantarflexion movements at the ankle. In addition, end-range dorsiflexion movements also triggered flexor reflexes in 3 subjects, although greater loads were required to trigger such reflexes using dorsiflexion movements (compared to plantarflexion movements). These three-joint reflex torque patterns triggered by ankle movement were broadly comparable to flexion withdrawal responses elicited by electrocutaneous stimuli applied to a toe, although the amplitude of the torque response was generally lower. We conclude that excitation of muscle and joint-related afferents induced by end-range movements may be responsible for exaggerated flexion reflex responses in spinal cord injury.
Schmit
B D
BD
Sensory Motor Performance Program, Rehabilitation Institute of Chicago, 345 E. Superior Street, Room 1406, Chicago, Illinois 60611, USA. bschmit@nwu.edu
McKenna-Cole
A
A
Rymer
W Z
WZ
D000328:Adult; D000843:Ankle Joint / Q000503:physiopathology*; D004576:Electromyography; D004594:Electrophysiology / Q000295:instrumentation / Q000379:methods; D006621:Hip Joint / Q000503:physiopathology; D006801:Humans; D007866:Leg; D008875:Middle Aged; D009068:Movement; D018482:Muscle, Skeletal / Q000503:physiopathology; D012018:Reflex; D012399:Rotation; D013035:Spasm / Q000209:etiology; D013119:Spinal Cord Injuries / Q000503:physiopathology*; D019415:Torque