Effects of changing wrist positions on finger flexor hypertonia in stroke survivors.
We sought to establish whether spastic hypertonia results from changes in intrinsic muscle properties or from altered stretch reflex properties. We hypothesized that finger flexor spastic hypertonia is primarily of neural origin, and that the dynamics of spastic muscle responses to stretch should therefore reflect the dynamics of muscle spindle receptor responses. In 12 stroke survivors, we recorded torque and electromyographic (EMG) responses of extrinsic finger flexors to constant-velocity rotation of the metacarpophalangeal (MCP) joints of the affected hand, over a range of initial muscle lengths. Stretch velocity was set to 6 degrees, 50 degrees, 150 degrees, or 300 degrees per second. Muscle length changes were imposed by changing wrist angle between 0 degree, 25 degrees, and 50 degrees of flexion. We found that reflex torque and EMG responses exhibited both velocity and length dependence, and there were significant interactions between velocity and length, replicating known characteristics of muscle spindle receptors. Our results support the hypothesis that finger flexor hypertonia is primarily of neural origin, and that it accurately reflects spindle receptor firing properties.
Li
Sheng
S
School of Physical Therapy and Rehabilitation Science, University of Montana, Missoula, 59812, USA. sheng.li@umontana.edu
Kamper
Derek G
DG
Rymer
William Zev
WZ
D000328:Adult; D000368:Aged; D004576:Electromyography; D005260:Female; D005385:Fingers / Q000033:anatomy & histology / Q000502:physiology*; D006801:Humans; D008297:Male; D008662:Metacarpophalangeal Joint / Q000502:physiology / Q000503:physiopathology; D008875:Middle Aged; D009068:Movement / Q000502:physiology*; D009122:Muscle Hypertonia / Q000503:physiopathology*; D009128:Muscle Spasticity / Q000503:physiopathology; D009470:Muscle Spindles / Q000502:physiology; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000502:physiology / Q000503:physiopathology; D012026:Reflex, Stretch / Q000502:physiology; D020521:Stroke / Q000503:physiopathology*; D014953:Wrist / Q000502:physiology*