Experimental muscle pain does not cause long-lasting increases in resting electromyographic activity

The mutual links between muscle pain and resting electromyographic (EMG) activity are still controversial. This study described effects of experimental muscle pain on resting EMG activity in a jaw-closing muscle and a leg muscle. Pain was induced by injections of hypertonic saline into the muscles in 10 subjects. Injections of isotonic saline served as a control. The pain intensity was scored on visual analog scales (VAS) and surface and intramuscular wire EMGs were obtained from the resting muscles before, during, and after saline injections. EMG activity was analyzed in 30-s intervals and demonstrated, in both muscles, significant increases 30-60 s after injection of hypertonic saline, but not after injection of isotonic saline. In contrast to the transient increase in EMG activity, the pain sensation lasted up to 600 s after injection of hypertonic saline. It was concluded that acute muscle pain is unable to maintain longer-lasting resting muscle hyperactivity.