Effects of two different self-adapted occlusal splints on electromyographic and force parameters during elbow flexors isometric contraction

The study was aimed at determining the acute effects of two types of occlusal splints on maximum isometric strength and fatigue of the elbow flexors muscles. The hypothesis was that splint-induced masticatory muscle repositioning might improve primary muscles recruitment by stretching masticatory muscles especially with the thicker splint.On nine physically active volunteers with no temporo-mandibular joint and masticatory muscles disorders, we assessed maximum voluntary contraction (MVC) of the elbow flexors with diurnal (OSD, 1-mm thick) and sport (OSSP, 3-mm thick) splints, and without splint (control, Ctrl). On different days, participants performed 60s of isometric contraction at 100%MVC (100%60s) and 80%MVC contraction until exhaustion (80%exh) under OSD, OSSP, and Ctrl in random order. Time of force output within target (t-target), force distance from target (ΔF), and force coefficient of variation (CoV) were calculated. Percentage of force decay (ΔFi-Fe) was determined during 100%60s. From the electromyographic (EMG) signal, root mean square (EMG RMS) and mean frequency (EMG MF) were determined. Neuromuscular efficiency was calculated as the ratio between force and EMG RMS.MVC and neuromuscular efficiency were significantly higher in OSSP and OSD than in Ctrl. During MVC, EMG MF was significantly lower in both splint conditions and EMG RMS showed a non-statistical tendency to lower values under both splint conditions. During 80%exh t-target was longer in OSD and OSSP (+7.8% and +5.2%, respectively) than in Ctrl. ΔFi-Fe was lower in OSSP than in Ctrl and OSD.These results support the hypothesis of a neuromuscular efficiency improvement of the elbow flexors possibly induced by acute, splint-induced masticatory muscles repositioning.