I often will use 5% lidocaine for its semi-neurolyic effects to knock out muscle triggers but worry about potentially weakening the muscle. In areas where muscle strength is imperative like some cases of neck and shoulder pains, I will dry needle instead. Now, in a case of shoulder pain, it was shown that dry needling was associated with increased muscle thickness so obviously not causing muscle weakness.
Cross, K. M., & McMurray, M. (2017).
Dry needling increases muscle thickness in a subject with persistent muscle dysfunction: a case report. International Journal of Sports Physical Therapy, 12(3), 468.
“The results of this case report suggest that dry needling contributed to improvement in muscle thickness and strength in a subject with muscle dysfunction following an injury.”
Comment – a relief for me as would not want to do any harm.