The Effects of a Self-Adapted, Jaw Repositioning Mouthpiece and Jaw Clenching on Muscle Activity during Vertical Jump and Isometric Clean Pull Performance

Purpose: The purpose of this study was to investigate the effects of a self-adapted, jaw repositioning mouthpiece and jaw clenching on muscle activity during the countermovement vertical jump (CMVJ) and isometric mid-thigh clean pull (MTCP). Methods: Thirty-six healthy, recreationally trained males (n=36; age, 23 ± 2.8 years; height, 178.54 ± 9.0 cm; body mass, 83.09 ± 7.8 kg) completed maximal CMVJ and MTCP assessments under six experimental conditions: jaw repositioning mouthpiece plus clenching (MP+C), jaw repositioning mouthpiece with jaw relaxed (MP), traditional mouthguard plus clenching (MG+C), traditional mouthguard with jaw relaxed (MG), no mouthpiece plus clenching (NoMP+C) and no mouthpiece with jaw relaxed (NoMP) while muscle activity of the dominant leg medial gastrocnemius (G), medial hamstring (H), vastus medialis (VMO), and erector spinae (ES) was recorded. Results: Repeated measures ANOVA revealed no changes in MTCP muscle activation for any mouthpiece or clench condition. Jaw clenching, regardless of mouthpiece condition, significantly improved prime mover muscle activation during CMVJ (p < .001). Prime mover muscle activation was significantly greater during CMVJ assessment for jaw repositioning mouthpiece and no mouthpiece conditions over the use of a traditional mouthguard (p < .001), but the repositioning mouthpiece did not lead to improved muscle activation compared to no mouthpiece (p > .05). Conclusion: These findings support jaw clenching as a viable technique to elicit concurrent activation potentiation (CAP) of prime mover muscle activity during dynamic but not isometric physical activity. Keywords: jaw repositioning mouthpiece, jaw clenching, concurrent activation potentiation, muscle activatio