The purpose of this study was to investigate the role of latent neuro-trigger points (LNTP) in the posterior deltoid with an isometric contraction of the anterior deltoid. The influence of LNTP on reciprocal inhibition at the shoulder was in question. The investigators recruited 14 asymptomatic subjects with LNTP in the posterior deltoid for this observational design. Force production of the anterior deltoid was measured as maximum voluntary contraction (MVC) measured with a transducer. Indwelling EMG needles were used to measure the spontaneous electrical activity (SEA) of the LNTP. EMG needles were placed in both non-LNTP and LNTP. The investigators reported that the posterior deltoid intramuscular EMG activity was significantly higher at rest in the LNTP compared to the non-LTNP. In addition, the LNTP EMG activity of the posterior deltoid was significantly higher than the non-LNTP with active MVC of the anterior deltoid. Furthermore, subjects reported significantly higher pain levels with the needle insertions to the LNTP than the non-LNTP. Furthermore, 6 of the subjects reported referred pain to either the back of the shoulder or upper arm. The conclusion is that LNTP may impair the neuromuscular system by inappropriately controlling the reciprocal inhibition process during agonistic muscle contraction of the anterior deltoid.

Ibarra J, Ge H, Wang C, Vizcaino V, Graven-Nielsen T, ARendt-Nielsen L. Latent Myofascial Trigger Points are Associated with an Increased Antagonistic Muscle Activity During Agonist Muscle Contraction. The Journal of pain. 2011;12(12):1282-8.

Clinical Relevance/Commentary: The increase in resting SEA within LNTP may cause unnecessary fatigue and overload to the muscle. LNTP may also reduce the necessary neuromuscular activity through impaired reciprocal inhibitory control. As a result, an athlete’s optimal performance may be limited and the presence of LNTP may increase their risk of sustaining injury. Based on these findings, it is important to look beyond a suspected local active trigger point and to assess as well as treat all the components of peripheral nervous system for maximum benefit of dry needling.