So What actually happens when you stick a needle in to a muscle? 

A study examining the response of the muscles after dry needling in mice identifies what actually happens.

Some dry needling treatments involve repetitive and rapid needle insertions into myofascial trigger points. This type of treatment causes muscle injury and can also damage nerve fibers. The aim of this study is to determine the injury caused by 15 repetitive punctures in the muscle and the intramuscular nerves in healthy mouse muscle and its ulterior regeneration.

Methods. We repeatedly needled the levator auris longusmuscle of mice, and then the muscles were processed with immunohistochemistry, methylene blue, and electron microscopy techniques.

Results. Three hours after the dry needling procedure, the muscle fibers showed some signs of an inflammatory response, which progressed to greater intensity 24 hours after the procedure. Some inflammatory cells could still be seen when the muscle regeneration was almost complete seven days after the treatment. One day after the treatment, some changes in the distribution of receptors could be observed in the denervated postsynaptic component.

Reinnervation was complete by the third day after the dry needling procedure. We also saw very fine axonal branches reinnervating all the postsynaptic components and some residual sprouts the same day. Conclusion. Repeated dry needling punctures in the muscle do not perturb the different stages of muscle regeneration and reinnervation.

(Domingo A, Mayoral O, Monterde S, Santafé MM. Neuromuscular Damage and Repair after Dry Needling in Mice.

Evidence-based Complementary and Alternative Medicine : eCAM 2013;2013:260806. doi:10.1155/2013/260806.)