Voluntary teeth clenching during exercise in a natural environment: prevalence and gender differences

Abstract

Background/Objectives: Voluntary teeth clenching (VTC) has been researched with respect to performance enhancement, but little evidence has verified its prevalence. This study's objective was to determine if VTC occurred during exercise in a natural environment. Secondarily, if differences in VTC existed based on gender and exercise type were investigated. Methods: Ambulatory surface electromyography (EMG) recorders were used to measure activities in the masseter and temporalis muscles and detect VTC during leg extension and general weight-lifting exercises in 7 male and 10 female subjects recruited from UMKC soccer teams. All subjects gave informed consent to participate in IRB-approved study protocols. Laboratory surface EMG recording during static and dynamic biting tasks established linear regression relations between EMG:bite-force for each subject. Then subject-specific thresholds for VTC ranging from 5-80% of a 20 N bite-force (T20N) were applied to detect and measure VTC in ambulatory data. Duty factors (DF=time clenching/total recording time, %) were compared for each VTC threshold and gender/exercise/muscle combination by simple test effect. Statistical significance was set at p<.05 with a Bonferroni correction. Results: VTC was shown by all subjects at a threshold of ≤5%T20N, by 47% of subjects at a threshold of 50%T20N, and by 29% of subjects at a threshold of 80%T20N. Females tended to have a higher DF at all thresholds during weight-lifting (highest DF at 5%T20N: 5.8%), while males tended to have higher DF during leg extensions (highest DF at 5%T20N: 7.1%). Gender differences in DF were significant during weight-lifting at all thresholds except at 80%T20N and during leg extensions at levels ≤25%T20N; and showed larger effect sizes for standardized leg extension compared to general weight-lifting exercises. Conclusions: Low level clenching was common during weight bearing exercises. Prevalence depended on threshold magnitudes defining clenching. There were gender, exercise-type and muscle differences in VTC.