Immediate Effects of Dry Needling on the Autonomic Nervous System and Mechanical Hyperalgesia: A Randomized Controlled Trial

This randomized controlled trial investigated the mechanisms by which dry needling (DN) produces its analgesic effects, focusing specifically on the autonomic nervous system response and pain processing. The study included 65 healthy volunteers with latent trigger points in the left adductor pollicis muscle, randomly divided into two groups: real dry needling and placebo with a non-penetrating needle. The methodology rigorously followed the CONSORT 2010 and STRICTA criteria, ensuring high methodological quality. Researchers used NeXus 10 MK-II biofeedback equipment to monitor physiological variables including skin conductance, heart rate, peripheral temperature, and respiratory rate.

Salivary cortisol samples were collected to assess hypothalamic-pituitary-adrenal axis activation. Pressure pain threshold was measured both locally and at a remote point on the tibialis anterior muscle. The most significant results showed that DN produced an immediate 20.6% increase in heart rate compared with only 5.3% in the placebo group (p=0.001, d=1.02), indicating sympathetic nervous system activation. Regarding pain processing, there was significant improvement in pressure pain threshold both locally (p=0.001, d=0.85) and remotely (p=0.022, d=0.58), demonstrating activation of central pain inhibition mechanisms.

Interestingly, no correlations were found between the intensity of pain perceived during the procedure and the physiological responses, suggesting that the observed effects are not simply the result of stress from needle insertion. The study also assessed other autonomic variables such as skin conductance, temperature, and respiratory rate, but found no significant differences between groups, although a temporal effect was observed in both groups. Salivary cortisol levels increased 11.27% in the DN group versus only 1.51% in the placebo group, but this difference did not reach statistical significance, possibly due to the timing of sample collection. The clinical implications are important because they provide scientific evidence that DN acts through activation of the sympathetic nervous system and stress-induced analgesia mechanisms, partially explaining its therapeutic effects.

The improvement in pain threshold both locally and remotely suggests that DN does not act only on local tissues, but also activates central pain modulation systems, including descending inhibitory pathways. These findings are consistent with theories proposing that DN may function through mechanisms similar to those of acupuncture, activating endogenous pain control systems. The study has some important limitations, including the fact that it was conducted only in healthy individuals, which may limit generalizability to chronic pain populations where pain processing mechanisms may be altered. In addition, the follow-up duration was very short, focusing only on immediate effects, and the timing of cortisol collection may not have been optimal for capturing the maximal HPA axis response.