Delayed onset muscle soreness: effect of an ischaemic block upon mechanical allodynia in humans.

The current study, for which ethical approval was obtained, was designed to assess the extent to which the tenderness or mechanical allodynia observed in delayed onset muscle soreness (DOMS) might be mediated by large diameter myelinated nerve fibres. Healthy human volunteers were recruited and randomly allocated to one of three groups: Normal-Control, Ischaemic-Control, and Test-DOMS (total n=21; n=7 in each group). In the Normal-Control group, subjects attended on a single occasion for assessment of mechanical pain threshold (MPT) at standardized sites over the biceps brachii using a pressure algometer for a period of 20 min. In both remaining groups, ischaemia was induced in subjects' non-dominant upper limbs by elevation of the limb, followed by application of a sphygmomanometer cuff at a pressure of 250 mmHg. Throughout the period of the block (20-40 min), sharp/blunt sensation was assessed at regular intervals. MPT was assessed upon inflation of the cuff and reassessed at 10 min intervals until deflation. In the two ischaemic block groups, current level of pain was also monitored using a computerized visual analogue scale (VAS) at the beginning and end of the procedure. Subjects in the Test-DOMS group attended 48 h prior to ischaemic block for induction of DOMS using a standardized regime of eccentric exercise, but thereafter were treated in exactly the same manner as the Ischaemic-Control group. Results showed a significant (P<0.05; ANOVA) increase in MPT in the Test-DOMS group by the 20 min point, corresponding to a 'normalization' of MPT; loss of the ability to distinguish between sharp/blunt sensation accompanied such changes. Parallel increases in reported pain were seen in both groups undergoing ischaemic block, indicating that the procedure did not alter nociception. While not definitive, these results suggest that altered processing of activity in large diameter (myelinated) afferents might underlie the mechanical allodynia observed in DOMS; thus, this is an area which warrants further investigation.