Influence of cold shivering on fine motor control in the upper limb.

The aim of the investigation was to determine the effects of cold shivering on the accuracy of force output in distal, middle and proximal muscles of the upper limb. Test of hand grip strength, elbow flexion and shoulder flexion (each done at 10% maximal voluntary contraction for 15 s) were done under three conditions: (1) thermoneutral air (27 degrees C), a condition of thermal comfort; (2) cold air (10 degrees C), a condition eliciting an increase in tonic muscle activity; (3) and cold air (10 degrees C) with a cold drink (8 degrees C), a condition that causes visible shivering. The averaged (root mean square) electromyogram (AEMG) and mean power frequency (MPF) were measured from proximal, middle and distal arm muscles during the tests and compared. The control of force output was highly effective at thermoneutral condition for all motor tasks. During the cold air condition, all muscles were tonically active but there was no effect on accuracy of test performance. However, AEMG increased approximately 20% (P < 0.05) with respect to test performance in thermoneutral condition. During the cold air/cold drink condition, all muscles were shivering to a different extend. AEMG during test performance increased 30-150% in comparison to thermoneutral condition (P < 0.05). In this case, hand grip and elbow flexion were not adversely affected (these tests require middle and distal muscles) by cold shivering. However, the accuracy of performance of shoulder flexion was adversely affected. This is consistent with the fact that proximal muscles are more active during cold shivering.