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 diamete r myelinated nerve fibres. Healthy human volunteers were recruited and rand omly allocated to one of three groups: Normal-Control, Ischaemic-Control, a nd Test-DOMS (total n = 21; n = 7 in each group). In the Normal-Control gro up, subjects attended on a single occasion for assessment of mechanical pai n threshold (MPT) at standardized sites over the biceps brachii using a pre ssure 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 m mHg. Throughout the period of the block (20-40 min), sharp/blunt sensation was assessed at regular intervals. MPT was assessed upon inflation of the c uff and reassessed at 10 min intervals until deflation. In the two ischaemi c block groups, current level of pain was also monitored using a computeriz ed visual analogue scale (VAS) at the beginning and end of the procedure. S ubjects in the Test-DOMS group attended 48 h prior to ischaemic block for i nduction of DOMS using a standardized regime of eccentric exercise, but the reafter were treated in exactly the same manner as the Ischaemic-Control gr oup. 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 accom panied such changes. Parallel increases in reported pain were seen in both groups undergoing ischaemic block, indicating that the procedure did not al ter nociception. While not definitive, these results suggest that altered p rocessing of activity in large diameter (myelinated) afferents might underl ie the mechanical allodynia observed in DOMS; thus, this is an area which w arrants further investigation. (C) 2000 International Association for the S tudy of Pain. Published by Elsevier Science B.V. All rights reserved.