Neurophysiological effects of latent trigger point dry needling on spinal reflexes

This pioneering research investigated how dry needling at trigger points (small painful nodules in muscles) affects spinal cord function and muscle reflexes. The study was motivated by the growing clinical use of dry needling to treat pain and spasticity, but with limited scientific knowledge about its neurological mechanisms of action. The researchers recruited 17 healthy adults who had latent (inactive) trigger points in the medial gastrocnemius muscle of the calf. These latent trigger points are common even in healthy people and can affect muscle function.

The experimental protocol included detailed neurological assessments at four time points: before treatment, immediately after, 90 minutes later, and 72 hours after a single session of dry needling. Measurements included spinal reflexes (H-reflex and reciprocal inhibition), M-waves (which assess neuromuscular integrity), and passive ankle range of motion. During dry needling, the researchers identified the trigger points through palpation and inserted disposable acupuncture needles until eliciting a local twitch response, followed by vertical needle movements for 25-30 seconds until those twitches were eliminated. The results revealed complex and specific effects.

In the treated muscle (medial gastrocnemius), M-wave amplitude decreased significantly soon after treatment (14% reduction) and at 90 minutes (18% reduction), returning to normal at 72 hours. This pattern did not occur in adjacent untreated muscles, indicating specific local effects likely related to temporary microlesions of muscle fibers and nerve endings. Surprisingly, although the H-reflex (an excitatory reflex) did not change significantly, reciprocal inhibition of the soleus muscle increased by 30% immediately after treatment and by 36% at 72 hours. Reciprocal inhibition is a neurological mechanism in which the activation of one muscle automatically inhibits its antagonist, and its increase suggests changes in the excitability of inhibitory spinal circuits.

Ankle dorsiflexion range of motion improved by 4 degrees immediately and by 3 degrees at 72 hours, correlating temporally with changes in reciprocal inhibition. The findings are clinically relevant for several reasons. First, they demonstrate that dry needling produces specific neuroplastic effects in the spinal cord, not limited to the treatment site. Second, the selectivity of the effects — with inhibitory reflexes increasing while excitatory reflexes remained unchanged — suggests complex mechanisms that may be therapeutically useful.

Third, the temporal pattern of effects (immediate and at 72 hours) may inform treatment protocols and timing of complementary interventions. Limitations include the absence of a control group, a relatively small sample, and a healthy study population, limiting generalization to pathological conditions. The study represents an important advance in understanding the neurological mechanisms of dry needling, providing evidence that this technique produces measurable changes in spinal circuits that may explain its observed clinical benefits in conditions such as post-stroke spasticity.