Withdrawal reflexes in the upper limb adapt to arm posture and stimulus location.
BACKGROUND
Withdrawal reflexes in the leg adapt in a context-appropriate manner to remove the limb from noxious stimuli, but the extent to which withdrawal reflexes adapt in the arm remains unknown.


METHODS
We examined the adaptability of withdrawal reflexes in response to nociceptive stimuli applied in different arm postures and to different digits. Reflexes were elicited at rest, and kinetic and electromyographic responses were recorded under isometric conditions, thereby allowing motorneuron pool excitability to be controlled.


RESULTS
Endpoint force changed from a posterior-lateral direction in a flexed posture to predominantly a posterior direction in a more extended posture [change in force angle (mean ± standard deviation) 35.6 ± 5.0°], and the force direction changed similarly with digit I stimulation compared with digit V (change = 22.9 ± 2.9°).


CONCLUSIONS
The withdrawal reflex in the human upper limb adapts in a functionally relevant manner when elicited at rest.
Sensory Motor Performance Program, Rehabilitation Institute of Chicago, 345 East Superior Street, Chicago, Illinois, 60611, USA; Edward Hines, Jr., VA Hospital, Hines, IL, USA.
Carrie L
CL
Peterson
Zachary A
ZA
Riley
Eileen T
ET
Krepkovich
Wendy M
WM
Murray
Eric J
EJ
Perreault
D000222:Adaptation, Physiological / Q000502:physiology; D000328:Adult; D001132:Arm / Q000502:physiology*; D001696:Biomechanical Phenomena; D004558:Electric Stimulation; D004576:Electromyography; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D009046:Motor Neurons / Q000502:physiology*; D059225:Nociception / Q000502:physiology; D011187:Posture / Q000502:physiology*; D012018:Reflex / Q000502:physiology*
endpoint force; fingertip stimulation; humans; motor control; nociceptive; spinal reflexes