Background: Needling retention time is one acupuncture parameter that warrants investigation, in view of the limited information available from both acupuncture texts and research literature. This study compares the effects of two retention times (one and 21 minutes) on regional pressure pain threshold (PPT). One minute retention is consistent with the recommendations in the earliest extant traditional text (259AD) while retentions of 20-30 minutes are common practice.

Aim: To investigate the effect of needling retention time on regional PPT.

Methods: In this within subject study, 24 healthy subjects completed eight interventions scheduled at least one week apart, involving manual acupuncture to LI4 or a designated nonacupoint (NAP) on the hand; with real or simulated manipulation each three minutes and needle retentions of one or 21 minutes. Pre and post intervention PPT measurements were completed, using an algometer, at ten sites across the body. Statistical analysis (ANOVA) was done on the combined PPT values of the ten sites.

Results: For the pair of interventions at LI4 with manipulation, the mean % PPT change for the 21 minute intervention was significantly higher compare to the one minute intervention (9.1% cf 5.8%). However, for the pair of interventions at LI4 without manipulation, the mean % PPT change for the one minute intervention was significantly higher than the 21 minute intervention (7.5% cf 3.7%). For both the pairs of interventions at the NAP, with or manipulation, there were no significant changes in mean % PPT change between the one minute and 21 minutes interventions. All eight interventions elicited statistically significant increases from baseline values (3.7%-9.1%).

Conclusion: The only significant difference in effects on PPT among same site comparison pairs was between the LI4 pair with manipulation present where the 21 minute retention elicited a greater change in mean PPT than the one minute intervention.