The use of a mouthpiece for injury prevention in sports such as football and lacrosse is a recommended (1) and required practice (22), which can be traced back to the 19th century when a British dentist, Woolf Krause, fitted boxers' teeth with strips of tree bark before fights for protection against dental injury (23). In the mid-to-late 20th century, reports of potential performance benefits, particularly improvements in strength, resulting from the use of an oral appliance to properly align the temporomandibular joint (TMJ) were described (18,19,24–27). Although compelling, these observations have been criticized for various reasons, including lack of statistical analysis, poor experimental design, and lack of experimental control (17,20,21). Still others have argued in favor of the ergogenic effects on athletic performance, even in the presence of the noted scientific flaws, suggested in the early research (11,15).
Similar to the performance enhancing effects of jaw realignment, jaw clenching has been examined for potential ergogenic effects. Hiroshi (16) observed significant increases in force production and rate of force development (RFD) during grip strength assessment of a nonathletic population when the jaw was clenched before and during force production. Ebben et al. (9) further examined the efficacy of jaw clenching vs. nonclenching in the countermovement vertical jump (CMVJ) of men's and women's track and field athletes. This group reported RFD, time to peak force, (TTPF), and peak force (PF) to be greater in the clenched group and suggested an increased neural drive. Although the study aimed to examine the influence of jaw clenching, participants were asked to jump while maximally biting on a vinyl mouthpiece and again with their mouth open.
Recent investigations examining the effect of jaw position and use of mouthpiece on performance variables such as aerobic performance factors (4,13,28), various reaction time measures (4,14), hormonal response (12), and muscular strength and power (3,5,6) have produced mixed results. Cetin et al. (5) examined the influence of a custom mouthpiece on various strength and power measures in taekwondo athletes. Although no significant differences were observed for sprint time, vertical jump measures, handgrip, and other isometric strength measures, significant improvements in peak and average power during the Wingate anaerobic test and increased hamstring isokinetic peak torque were reported when a custom mouthpiece was worn. Arent et al. (3) reported significant improvements in vertical jump height and peak power during the Wingate test when a performance mouthpiece was worn by professional and collegiate athletes compared with tests not using a mouthpiece in the same participant group. However, submaximal bench press performance and mean power during the Wingate test were not different between conditions. In both articles, it was unclear if the participants were asked to perform normally or asked to bite against the mouthpiece during the testing session.
A recent study by Dunn-Lewis et al. (6) compared the use of a performance mouthpiece, regular mouthpiece, and a control condition during a battery of performance tests. Current and former collegiate athletes were asked to perform normally in all 3 mouthpiece conditions. This group reported that both strength and power measures were elevated in the bench press throw in participants using a performance mouthpiece compared with the other conditions. Further, the rate of power development and plyometric performance were improved in males while using the mouthpiece compared with the regular mouth guard or control condition.
Although the recent research scrutinizing strength and power shows potential positive benefits of mouthpiece use, most of these investigations were done with highly trained athletic populations (3,5,6). Furthermore, these studies examined custom-made potentially expensive mouthpieces (3,5,6). Research examining relatively inexpensive commercially available performance mouthpieces and the potential effects on strength and power performance is lacking. Also, examination of a recreationally trained population to determine if similar ergogenic effects as those observed in the highly trained athletic population can be reproduced is warranted. Therefore, the purpose of this study was to investigate a commercially available, boil-and-bite, performance mouthpiece and its effects on acute measures of power and strength, specifically, the 1 repetition maximum (1RM) bench press and CMVJ in comparison to no mouthpiece use in a recreationally trained population.
Experimental Approach to the Problem
This study examined the hypothesis that the use of a performance mouthpiece would provide an ergogenic effect on 1RM bench press and vertical jump performance in comparison to no mouthpiece use. A within-subjects design was used in which each subject was randomly assigned the use of a mouthpiece during 1 of the 2 identical testing sessions.
Experimental testing consisted of 3 laboratory visits. The first visit involved obtaining informed consent, subject familiarization with experimental procedures, and providing the mouthpiece (ArmourBite Mouthpiece; Under Armour, Baltimore, MD, USA) to the participant with instructions on proper fitting. As recreationally trained participants, all were familiar and experienced with the bench press exercise. For the vertical jump testing procedures, each participant was allowed to perform several submaximal jumps from the force platform while making contact with the Vertec device (Sports Imports, Columbus, OH, USA). Participants were also asked to refrain from engaging in any behavior that would negatively impact the outcome of the assessments, including but not limited to vigorous physical activity before testing, consumption of alcohol, or abnormal eating or sleeping. The remaining 2 visits were testing sessions where the experimental protocol was administered. Each participant was asked to self-report their adherence to all instructions regarding exercise, alcohol consumption, etc., before testing.
Twenty-one physically active college-aged males (18–24 years old), with recreational sport and exercise experience, volunteered and completed the research protocol. Participants were deemed physically active if they participated in resistance training exercise at least 3 days per week consistently for the previous 3 months. All participants (n = 21; age, 21.5 ± 1.3 years; height, 177.5 ± 7.9 cm; body mass, 87.1 ± 10.8 kg) were injury free at the time of testing, and all signed University approved Institutional Review Board consent documents.
The testing sessions were performed at the same time of the day and separated by exactly 1 week. The order of completion of the 2 experimental conditions, with mouthpiece (MP) and without mouthpiece (noMP), was randomized for all participants. Based on previous methodologies (6) and the directions for use provided with the mouthpiece, participants were instructed to perform as normally as possible. It has been stated that clenching of the jaw musculature during maximal muscular effort is a fairly common occurrence (8). Therefore, no instructions were given to clench or not to clench during testing.
Each experimental condition involved a dynamic warm-up consisting of 5 minutes of cycling on a Precor upright bike (Precor, Inc., Woodinville, WA, USA) at 70 rpm, followed by dynamic stretching supervised by National Strength and Conditioning Association, Certified Strength and Conditioning Specialists. After the warm-up, participants were asked to perform a maximum CMVJ measurement and 1RM protocol for the bench press exercise. The maximum CMVJ and 1RM bench press assessment procedures used are outlined below.
Countermovement Vertical Jump Assessment Procedures
The CMVJ assessment procedures are consistent with those described by Semenick (23). The jumps were performed on a force plate, and a commercial Vertec measurement device (Sports Imports) was also used. Each participant was instructed to determine their maximum reach height by standing flat-footed, directly underneath the Vertec device and reaching up with the dominant hand to push forward the highest vane that could be reached. The height of the device was then increased to accommodate a maximal effort CMVJ. The participant was then instructed to perform each CMVJ trial without moving the feet before take off, to jump maximally, and to tap the highest vane possible at the apex of the jump. Trials were scored as the vertical distance, to the nearest 1-half inch between the reach height and height of vane tapped during the jump. Each participant was given 3 trials for both the MP and noMP conditions. The trial producing the highest value was used for analysis.
One Repetition Maximum Bench Press Assessment Procedures
Bench press 1RM was assessed using a standard Olympic barbell (York Barbell Co., York, PA, USA), standard weight plates (Iron Grip Barbell Company, Santa Ana, CA, USA), and a single station bench press bench (BodyMasters, Rayne, LA, USA). The 1RM assessment protocol used was previously described by Earle (7). The participant was instructed to execute 3 warm-up sets; the first with a resistance allowing 5–10 repetitions, the second and third with a 5–10% increase of the previous resistance load, allowing for 3–5 repetitions for each set. A 1- to 2-minute rest period was provided between the first to second and second to third sets, respectively. After the third warm-up set, a 2- to 4-minute rest period was provided, a 5–10% load increase was made, and the subject was instructed to attempt a 1RM. This 2- to 4-minute rest period, 5–10% load increase, and 1RM attempt was repeated until the 1RM attempt was unsuccessful. The last successful 1RM attempt was reported as the participants' 1RM. All participants' 1RM was successfully determined within 5 testing sets under each condition.
Instrumentation and Data Processing
All jumps were executed from a 600 mm × 400 mm force platform (Bertec, Inc., Columbus, OH, USA). Kinetic data were recorded at a sampling rate of 1,080 Hz. Ground reaction force (GRF) data were used for the identification of PF, relative PF, and calculation of RFD at 120, 200, and 250 ms relative to the onset of concentric force production. Relative PF data were determined by dividing the PF by subject body weight and expressed as a function of body weight (%BWPF).
Rate of force development was calculated according to methods previously described by Aagaard et al. (2). Derived from the vertical force components of the force-time record during the CMVJ of maximal obtained height, RFD was calculated as the slope of the GRF curve over time intervals of 0–120, 0–200, and 0–250 ms relative to the onset of concentric force production. Concentric force production was considered to begin when the vertical force component of the GRF curve exceeded body mass as measured by the force plate.
All data were analyzed via paired-sample t-tests to compare differences between the MP and noMP conditions. All analyses were performed with an alpha level of p ≤ 0.05, set a priori. Data were analyzed using IBM Statistics package software, version 20.0 (IBM SPSS Statistics, Armonk, NY, USA). A paired t-test was also used to analyze participants' body weights between each testing session to ensure no significant differences in body weight between testing sessions.
Data are presented as mean values ± SD. No significant (p > 0.05) differences were found between conditions for any of the variables measured. All data and p values from the t-tests are expressed in Table 1.
The specific aim of the present study was to determine whether the performance mouthpiece used provided an ergogenic effect on the performance of the CMVJ and the 1RM bench press exercise in recreationally trained men. No ergogenic advantage was seen as the result of mouthpiece use in the performance of the CMVJ or 1RM bench press exercise in this investigation. Although slight increases in PF and RFD during the CMVJ were observed in the MP condition in comparison to the noMP condition, these improvements were minimal and not statistically significant. Although the results of the present study initially appear contrary to previous studies, it must be noted that this investigation used recreationally trained males compared with highly trained athletes, which may, in part, explain the absence of an observed performance effect. Also pertinent to mention is that although no ergogenic advantage was provided by using the mouthpiece, no performance detriment was observed either.
Specifically in relation to CMVJ performance, Ebben et al. (9) observed statistically significant increases in RFD and TTPF in the CMVJ when the jaw was maximally clenched around a mouthpiece in comparison to an open jaw, no clench condition. Similarly, Hiroshi (16) observed significant increases in force production and RFD during grip strength assessment of a nonathlete population when the jaw was clenched before and during force production. To facilitate the clenching condition, subjects in the previous research were given specific instructions to clench the jaw maximally while performing the testing protocol. In the present investigation, jaw clenching was not mentioned to participants. Subjects were instructed to perform as normally as possible during both the MP and noMP mouthpiece conditions.
Three studies examining a jaw aligning mouthpiece and the resulting effects on performance used the CMVJ as an assessment measure, with 2 showing performance improvements (3,6) and 1 showing no changes (5). Similar to the present study, Dunn-Lewis et al. (6) gave no specific instructions to participants regarding clenching, but rather asked them to perform naturally. However, participants in that investigation were collegiate athletes whereas this research used recreationally trained participants. It is unclear whether any specific instructions to clench, not clench, or perform normally were given in the other 2 studies (3,5).
For the measure of strength, the 1RM bench press performance, no ergogenic effect was seen with the use of the performance mouthpiece. Most of the previous research reporting positive effects of mouthpiece use on muscular strength focused primarily on isometric muscle action (10,19,24,25). In a review, Forgione et al. (11) suggested that although there are inconsistencies and flaws in some previous research design, there is a positive relationship between jaw position, jaw alignment mouthpiece use, and isometric strength. This must be taken with some hesitancy as most of the review focuses on practices of orthodontic professionals and their treatment of TMJ patients, not strength and conditioning professionals. The results of the present study do not coincide with the results seen in some previous research, suggesting that the varying ergogenic effects reported may be limited to the specific performance mouthpiece used in the reporting investigation and to the specific training level of the participant group using the mouthpiece. Future investigations into the potential performance enhancing and ergogenic effects of mouthpiece use are warranted to confirm or refute specific product performance enhancing claims. Emphasis should be placed on controlling and quantifying the amount of jaw clenching, both with and without performance mouthpieces, in an attempt to determine the effectiveness of the mouthpieces because the relationship between jaw position, clenching, mouthpiece use, and performance enhancements has already been reported (8,10). Attempts to clarify specific mechanisms of action contributing to each potential ergogenic effect are also warranted.
Although clenching of the jaw musculature may very well lead to a potential ergogenic effect in comparison to not clenching (9,16), merely wearing a jaw aligning, performance mouthpiece does not appear to be sufficient in facilitating an increase in performance in a recreationally trained population. Future research is necessary to determine whether any ergogenic effect of clenching the jaw musculature is further facilitated by wearing a performance mouthpiece and to identify the mechanisms behind any observed changes in performance.
The authors confirm that there is no conflict of interest between the authors of this work and the participants, the materials and equipment used, or any other outlet involved in this research.
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