Background and aims
Ultrasound revolutionized myofascial pain treatment, precise muscle dry needling (DN) under ultrasound (US) guidance can multiply clinical effect. Local muscle response (a.k.a. local twitch response, LTR) associated with inactivation myofascial trigger points (MTrP), however, controversies remain in the issue.
The aim was to test hypothesis that local muscle response is associated with clinical effect of precise DN.
Methods
We included 38 patients (23 females, 36±7 years old) with chronic low back pain. The protocol by Bubnov [https://doi.org/10.1186/1878-5085-3-13] was applied: MTrP were identified according to clinical examination, reffered pain pattern, US identification; single fine (28G) steel needle DN under US guidance was applied to elicit LTR and/or `needle grasp`. We evaluated both phenomena, did M-mode to detect fasciculations during DN. Visual analogue scale data (VAS0-10) were measured before and after procedures.
Results
Main active MTrPs were detected in paravertebral (“central”) muscles, latent (“peripheral”) MTrP in limb muscles; all were effectively needled evoking muscle response; pain decreased by 90% VAS. We conducted 1-2 sessions per patient, 2-5 needles per session. During active MTrPs DN deeper 30 mm we detected fasciculations on M-mode during first 30-60 sec and `needle grasp` over 20 min; in larger muscles (complex architecture) we observed both effects; in small and deeper located muscles – `needle grasp` only; in superficial and latents MTrPs - LTR only. Retention of needles correlated with LTR duration and clinical effect. 
Conclusion 
Muscle response to DN is crucial for effective treatment myofascialpain, depends on MTrPs acitivity, needling depth and muscle architecture.

IMPLICATION OF LOCAL MUSCLE RESPONSE TO PRECISE DRY NEEDLING IN CLINICAL OUTCOMES OF TREATMENT MYOFASCIAL PAIN