Pressure pain threshold changes after repeated mechano-nociceptive stimulation of the trapezius muscle:: Possible influence of previous pain experience

We examined the relation between repeated noxious pressure over the trapezius muscle and changes in pressure pain thresholds (PPTs) in a before-after trial design. A conditioning series of 30 mechano-nociceptive stimuli was applied manually with a handheld algometer probe, and PPTs were measured over 1 trapezius muscle (skin anaesthetized) in 27 healthy women before and after the intervention. With a mean stimulation rate of 0.40 Hz and a mean nociceptive stimulation intensity of 1.78 x Threshold, subjects were found to systematically react with a change in PPT, either a decrease or an increase. Normalized data, transformed into mean unidirectional PPT differences, showed statistically highly significant changes after intervention. The relative risk of reacting with lowered PPTs on noxious stimulation was 3.7 times higher for subjects who had not given birth to children than for subjects who had given birth to 1 or several children (P <.046). When 11 subjects were tested at a second session, a clear correlation of PPT reactions (r = 0.527; P <.001) was found. In summary, repetitive mechano-nociceptive stimulation of the trapezius muscle in healthy females evokes moderate and temporary changes in PPT that last for at least 35 minutes after cessation of stimulation. Perspective: A possible development of the response with transiently decreased PPTs into a model for human muscle pain is an intriguing possibility, since other models usually involve the introduction of chemical or thermal agents in the muscle, but this must await further research. (C) 2007 by the American Pain Society.