Activity in nociceptive primary afferent fibers and clinical muscle pain

Abstract

The Focus article by Simone and associates gives a quite complete overview of the current knowledge and concepts concerning the peripheral mechanisms of muscle pain. Regarding the question of the adequate stimulus for muscle nociceptors, the available data indicate that there are several kinds of nociceptors, each of which has its own adequate stimulus or combination of stimuli. Even though activity in group III fibers is likely to elicit subjective sensations identical to those induced by group IV muscle afferents, some pathophysiologic situations excite predominantly one fiber population. For instance, the pain of ischemic contractions appears to be due largely to activity in group IV afferents. Generally, the effects of input from muscle group IV afferent fibers on dorsal horn neurons in experimental animals are small. Following longer-lasting nociceptive afferent activity to the spinal cord, however, the efficacy of the group IV input rises. This could mean that acute muscle pain is mediated largely by input via group III fibers, whereas chronic muscle pain is dominated by group IV input.