Electronic Theses and Dissertations

Date of Award


Document Type


Degree Name

Ph.D. in Health and Kinesiology


Health, Exercise Science, and Recreation Management

First Advisor

John C. Garner

Second Advisor

Melinda Valliant

Third Advisor

Yang-Chieh Fu

Relational Format



Jaw clenching has been demonstrated to elicit concurrent activation potentiation (CAP), which is the ergogenic advantage of increased prime mover muscular force production during physical activity. Further, jaw aligning mouthpieces have been shown to improve the force production capabilities of individuals with temporomandibular joint disorder (TMD) and are purported to have similar effects on persons without symptoms of TMD. Previous research examining these phenomena has focused solely on jaw alignment via mouthpiece use or jaw clenching as mutually exclusive factors explaining the reported performance benefits. However, these factors do not appear to be mutually exclusive. No previously published investigations have attempted to determine whether observed performance improvements can be attributed exclusively to jaw clenching, jaw alignment via mouthpiece use, or if the combination of clenching and the presence of a mouthpiece further facilitates performance improvement. Therefore, the purpose of this study was to examine the effects of jaw clenching, jaw alignment via mouthpiece use, and the combination of the two on measures of force production and muscle activation. Participants (n=36) were required one familiarization visit and three testing visits to the lab. The familiarization visit consisted of participant prescreening, obtaining informed consent, basic anthropometric measurement, mouthpiece fitting and instruction, and familiarization of the countermovement vertical jump (CMVJ) and isometric mid-thigh clean pull (MTCP) assessments. The testing conditions, counterbalanced for all participants were as follows: performance mouthpiece with jaw clenched (PMP-C), performance mouthpiece with jaw relaxed (PMP), traditional mouthpiece with jaw clenched (MP-C), traditional mouthpiece with jaw relaxed (MP), no mouthpiece with jaw clenched (NoMP-C), and no mouthpiece with jaw relaxed (NoMP). The dependent variables examined were rate of force development (RFD), peak force (PF), relative peak force (nPF), and muscle activation during both CMVJ and MTCP assessments. A 3 x 2 (mouthpiece x clench condition) ANOVA for repeated measures was conducted to analyze each of the dependent performance variables. Post-hoc analysis for multiple comparisons were performed using a Bonferroni correction. Paired samples t-tests were used to further analyze observed interaction significance. Results revealed that clenching significantly improved all measured force production variables during the MTCP (p < 0.05). There was no difference between clench conditions for the CMVJ assessment. There was no difference in any force production variables between mouthpiece conditions for either the CMVJ or the MTCP. Muscle activation, measured via electromyography, was significantly greater under clench conditions during the CMVJ assessment (p < 0.05). Jaw aligning mouthpiece and no mouthpiece conditions lead to greater muscle activation than the traditional mouthpiece condition during the CMVJ assessment as well (p < 0.05). There were no differences in muscle activation between conditions during the MTCP. These results support the use of jaw clenching as a viable strategy for eliciting CAP during isometric muscle actions. Future studies should attempt to identify the mechanisms behind the observed changes in force production, as the current results do not support increased neural drive as the underlying factor.

Included in

Kinesiology Commons



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