Sympathetic nerve activity does not reduce proprioceptive acuity in humans.
OBJECTIVE
Proprioception is essential in coordinating body segments and controlling muscles to perform movements. Animal studies have reported reduced muscle spindle sensitivity in jaw muscles during stimulation of sympathetic nerves. A stress-induced distortion of proprioception has been suggested that could lead to reduced fine control of movement and inefficient muscle use. The present study investigated whether increased muscle sympathetic activation alter human proprioception.


METHODS
Movement detection thresholds of the right ankle were determined in eight healthy subjects, before and during two conditions known to increase muscle sympathetic activity (MSA); a cold pressor test (CPT) and oral glucose ingestion (GLUC).


RESULTS
During a cold pressor test plasma noradrenaline (NA) and mean arterial pressure (MAP) increased significantly, compared with baseline (Ps<0.01), whereas the movement thresholds were unchanged (Ps>>0.05). After GLUC plasma NA and MAP increased significantly, compared with baseline (Ps<0.05). The movement threshold into flexion decreased (P=0.022), whereas into extension there was no change (P=0.28). The most prominent increase of plasma NA corresponded with a reduced movement detection threshold, suggesting increased muscle spindle sensitivity.


CONCLUSIONS
The present findings contradict previous reports from animal studies and the hypothesis that sympathetic nerve activity reduces proprioceptive acuity.
Matre
D
D
Department of Physiology, National Institute of Occupational Health, Oslo, Norway.
Knardahl
S
S
D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D003080:Cold Temperature; D005260:Female; D005947:Glucose / Q000008:administration & dosage; D006801:Humans; D008297:Male; D009068:Movement / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D009638:Norepinephrine / Q000097:blood; D011434:Proprioception / Q000502:physiology*; D012039:Regional Blood Flow / Q000502:physiology; D013564:Sympathetic Nervous System / Q000502:physiology*
D005947:Glucose; D009638:Norepinephrine