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The Effects of a Customized Over-the-Counter Mouth Guard on Neuromuscular Force and Power Production in Trained Men and Women

Dunn-Lewis, Courtenay; Luk, Hui-Ying; Comstock, Brett A.; Szivak, Tunde K.; Hooper, David R.; Kupchak, Brian R.; Watts, Ashley M.; Putney, Brendan J.; Hydren, Jay R.; Volek, Jeff S.; Denegar, Craig R.; Kraemer, William J.

Journal of Strength and Conditioning Research: April 2012 - Volume 26 - Issue 4 - p 1085–1093
doi: 10.1519/JSC.0b013e31824b4d5b
Original Research

Dunn-Lewis, C, Luk, H-Y, Comstock, BA, Szivak, TK, Hooper, DR, Kupchak, BR, Watts, AM, Putney, BJ, Hydren, JR, Volek, JS, Denegar, CR, and Kraemer, WJ. The effects of a customized over-the-counter mouth guard on neuromuscular force and power production in trained men and women. J Strength Cond Res 26(4): 1085–1093, 2012—Although mouth guards were originally designed for injury prevention, even elite athletes are now using performance mouth guards to improve athletic success. Both expensive custom models and over-the-counter models are available, but the efficacy is not well known. Some athletes remain wary of the perceived potential for detriments using a mouth guard to their performance. Thus, the purpose of this study was to examine various physical performance tests when using a mouth guard including a customized over-the-counter mouth guard. Twenty-six trained men (25 ± 4 years; 1.78 ± 0.07 m; 83.3 ± 11.4 kg) and 24 trained women (23 ± 3 years; 1.65 ± 0.08 m; 62.6 ± 7.8 kg) volunteered for the investigation. The subjects completed a familiarization period and then balanced and randomized treatment conditions that included: (a) a customized Power Balance performance mouth guard (PB MG); (b) a regular over the counter boil-and-bite mouth guard (Reg MG); and (c) a no mouth guard (No MG) treatment condition. At each visit, the subjects completed a testing protocol that was sequenced in the following order: sit-and-reach flexibility, medial-lateral balance, visual reaction time, vertical jump, 10-m sprint, bench throw, and plyo press power quotient (3PQ). Heart rate and rating of perceived exertion (RPE) were recorded around the 3PQ. Significance was set at p ≤ 0.05. Expected significant sex differences existed for all power, strength, and speed variables. Bench throw power (watts) and force (newtons) were significantly higher under PB MG than either Reg MG or No MG or in both men and women. The 3PQ power and force production were higher than that for the other 2 treatments for the PB MG for men only. There were no significant differences for treatment conditions in the heart rate or RPE after the 3PQ test. Men were better able to maintain significantly higher 3PQ power production under PB MG treatment condition compared with the other 2 treatment conditions. Rate of power development was significantly higher in men for the vertical jump when using the PB MG compared with that for other treatment conditions in men only. No differences were observed in flexibility, balance, visual reaction time, or sprint time. The PB MG performance mouth guard improves performance of upper-body loaded power exercises in both men and women and lower body power exercise in men without compromising performance on any other performance parameters.

Human Performance Laboratory, Department of Kinesiology, University of Connecticut, Storrs, Connecticut.

Address correspondence to William J. Kraemer, william.kraemer@uconn.edu.

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Introduction

Whether for the modern use by professional athletes such as the New Orleans Saints, the historical management of pain (during Civil War amputations or Native American childbirth), or improved performance (on ancient Roman battlefields), oral appliances has long been used to mitigate the effects of anticipated stress on the body (35). This practice may be related to the effects that mastication (or chewing) has on the body. Mastication increases blood flow to areas of the cortex (associated with memory, attention, awareness) and cerebellum (motor control, timing, attention, and fear) (28). It increases the activation of the hippocampus (short- and long-term memory) and prefrontal cortex (planning) (19) while increasing arousal through the reticular formation (26). Chewing reduces the stimulation of the amygdala (emotional reaction) (4) and activates serotonin action in the brain (43). Although it is well known that mastication increases in response to stress in both rodents (4) and humans (25), its apparent ability to help the body manage physiological stress has not been fully appreciated until recently.

Mastication exerts its influence, in part, on the activity of both hypothalamo-pituitary-adrenal axis (important hormonal mediators during physiological stress such as exercise) (14). In a rat model, the action of biting an oral appliance in response to psychological challenge has been shown to suppress oxidative stress in the hypothalamus (27) including chemical markers thought to be involved in stress responses (nitric oxide [21]) and neuroplasticity (pERK1/2 [36]). Biting an appliance also suppresses stress-induced elevations in blood pressure, core temperature (as shown with thermal imaging), interleukin-1β, interleukin-6, and leptin while attenuating reductions in thyroid hormone (31). The expression of corticotrophin-releasing factor is also attenuated in mice provided with an oral appliance (22). In humans, the act of chewing reduces perception of daily stress (46), reduces salivary cortisol and anxiety, and improves alertness (38). Although mastication dysfunction appears to be related to cognitive deficiency (32), active mastication improves performance on learning and memory tasks, including spatial memory, short- or long-term recall, sustained mental performance, and reaction time (3,19,32,37,41,42,45). Overall, animal and cognitive studies indicate that the mastication of oral appliances plays an important role in managing and dissipating physiological stress in contexts outside of athletics.

In the realm of human performance, mouth guards are recommended for athletes of all ages and abilities as a safety measure (1) and required for many athletic events (23). Although their principal use in most athletes is safety, the use of mouth appliances for physical performance translated into formal scientific research as early as the 1960s (40). Investigators uncovered positive benefits to strength (39), endurance (13), and ventilation (12), although typically with the use of custom-designed oral appliances. Despite positive findings, Gelb et al. (18) noted in 1996 that much of the early research (regardless of positive or negative outcome) was riddled with fundamental methodological issues and often used expensive, custom-designed mouthpieces. More recent investigations have shown mixed impacts on aerobic performance (thought to act through increased ventilation), typically displaying small or insignificant differences, if any, in maximal oxygen consumption and other measures (16,34,44). One study demonstrated no performance differences between custom-designed and boil-and-bite mouth guards (6). Examined as a whole, research indicates that mouth guards may play a positive role in some athletic performances, but variations in its use, types, and performance measures has lead to experimental variations in results. However, fears for use with aerobic performances have been ruled out by prior research (6,34).

An area in which mouth guard use has shown promise is with short-burst, high-speed, or anaerobic activity. Although no differences were seen with mouth guard use in salivary cortisol with aerobic exercise (15), significant reductions were demonstrated after 1 hour of intense resistance exercise with mouth guard use (14). In 1 investigation, mouth guard use significantly decreased auditory switch-response reaction time (but not visual computer-input reaction time (17). In Taekwondo athletes, mouth guard use did not improve 20-m sprint time, vertical jump height, or strength measures but did increase peak and average Wingate Anaerobic power and peak isokinetic torque (8). In an investigation that used a mouth guard similar to the one examined here (with a design that provides some cushioning to clench on) investigators have shown significant differences in vertical jump height and peak (and not mean) Wingate anaerobic power, but not bench press strength (however the mouth guard that was not an over-the-counter product) (2). Based on these findings, high-speed anaerobic activities show promising performance benefits with mouth guard use and were therefore the focus of this investigation.

Interestingly, in reviewing the literature on mouth guard use and performance, 2 central concerns emerge. First and foremost, many investigations are initiated in response to athletes who do not routinely use mouth guards for fear of performance detriment (6,8,12,34,44). Although mouth guard use may simply provide a side performance benefit to those who routinely use them, the knowledge that benefits may exist may encourage otherwise resistant young athletes to wear mouth guards that have been historically thought of only as protective devices. Second, although the quality of research has improved over time and potential benefits to high-speed, anaerobic performance benefits show promise, there remains a paucity of experimental data on the topic of customized over-the-counter performance designed mouth guard use and performance. Thus, a need exists for a line of research examining potential benefits of more customized mouth guards that may impact various physical performance capacities. Therefore, the purpose of this investigation is to examine the impact of a customized performance mouth guard on physical performances with an emphasis on short-burst, high-speed, anaerobic tasks in trained men and women.

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Methods

Experimental Approach to the Problem

We used a strong experimental design with a balanced, randomized, placebo-controlled, within-group crossover investigation, which consisted of 3 visits after initial familiarizations and baseline visits. Three experimental treatment conditions were used in this investigation and consisted of (a) A Power Balance performance upper teeth mouth guard (PB MG), (Power Balance LLC, Laguna Niguel, CA, USA); (b) A regular off the shelf boil-and-bite upper teeth mouth guard (Reg MG) (placebo); or (c) no-mouth guard (No MG) (control) day. In this study, because of the limited evidence for a role in aerobic performances, experimental tests were selected to emphasize high-speed anaerobic power and force (e.g., plyo press power quotient [3PQ], bench throw, vertical jump). Sprint acceleration time, visual reaction time, flexibility, and balance were investigated to determine whether performance advantages of the mouth guard extended beyond strength and power capabilities. Additionally, if any advantages of mouth guard use exist, and these measures would determine if there were any collateral negative effects on other aspects of human performance that have made some athletes shy away from them (6,8,12,34,44). The subjects were not instructed to use the mouth guards in any specific manner for the testing but to do what came naturally to them therefore allowing each mouth guard to mediate any effects via its own design and comfort in each test.

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Subjects

Twenty-six men (age: 25 ± 4 years; height 1.78 ± 0.07 m; body mass 83.3 ± 11.4 kg) and 24 women (age: 23 ± 3 years; height 1.65 ± 0.08 m; body mass 62.6 ± 7.8 kg) participated in the investigation (men were significantly taller and heavier than the women). All the subjects were currently resistance trained and were athletes or former athletes in various collegiate sports (basketball, soccer, track and field, volleyball, lacrosse, football [men], rugby). All the volunteers were medically screened and cleared by a physician as healthy to participate and lacking in any confounding medical conditions. All the subjects had the experimental risks and benefits of the investigation explained to them before the study and then signed an informed consent document to participate. The investigation was approved by the University of Connecticut's Institutional Review Board for use of human subjects in research.

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Experimental Procedures

To standardize each testing day, each of the subjects kept a 24-hour diary, which included a diet record and fluid intakes. No exercise training was performed during the 24 hours before a testing protocol, and the testing took place at a similar time of day for each subject. This activity and diet record was replicated for each visit and a standard minimum of 2 cups of water were ingested in the evening and the morning of a testing protocol to insure proper hydration before each testing protocol. The same sequence of testing was performed each day. The protocol commenced with a standardized warm-up (5 minutes of moderate exertion cycling on a recumbent cycle ergometer). In a traditional sit-and-reach box test for hamstring-back flexibility, both legs were extended on the floor, and the subjects reached forward as far forward as possible on the box (as described elsewhere [7]). In a 20-second test of balance, the subjects stood on their nondominant leg on top of a force plate (Advanced Mechanical Technology, Inc., Watertown, MA, USA) as still as possible with hands on hips; medial-lateral dispersion was measured using DartPower 2.0 software (Athletic Republic, Park City, UT, USA). After a Quickboard visual reaction time test, a countermovement vertical jump test was performed (both described below). A 10-m sprint was then completed (from a standing position) using the Test Center Timing System (Brower Timing Systems, Draper, UT, USA). The subjects finished the testing protocol with a bench throw test and 3PQ (both described below). For all procedures except the 3PQ, the best score of up to three attempts for each test on a given condition's day was used for analysis as to not penalize a subject for any single subpar score (e.g., the fastest time on a given testing day for a 10-m sprint was used for analysis).

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Mouthguard Fitting

Both the customized PB MG and the Reg MG were over-the-counter upper teeth models. Fitting was performed with instruction and staff supervision using standard practices (most of the subjects were very familiar with fitting given their athletic backgrounds). For both mouth guards, boiling water was poured in a container and the mouth guard submerged for 30 (Reg MG) to 90 (PB MG) seconds. The subjects inserted the mouth guards into their mouths (taking care to keep the biting surfaces of the PB MG between their teeth) and sucked on the mouth guards until they had conformed to the individual subject's teeth. The customized nature of the PB MG, as noted by the company, used a scientific design to customize the design of the mouth guard to specifically produce a calculated spacing and resilience for an individual's bite to float into its most natural and comfortable position, resulting in harmony between the teeth, temporomandibular joint and muscles in the face. Each of the mouth guards was then checked for proper molding before storage and if not properly formed a new mouth guard was refitted.

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QuickBoard Visual Reaction Time Test

The QuickBoard system (The Quick Board, LLC, Memphis, TN, USA) comprised a visual stimulus board with 5 lights and a corresponding step pad. For our 20-second test, 1 of 5 lights illuminates. The subject steps on the pad located on the floor that corresponds to the illuminated light. Once the subject steps on the correct pad, a new light illuminates (and the subject must now step on the pad that corresponds to the new light). This continues in random sequencing over the 20-second trial. The average visual reaction time (time from light illuminating to correct response) was recorded for each of 3 trials. Again, the best of the 3 trials was used for analysis.

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Countermovement Vertical Jump Test

For each trial of the countermovement vertical jump test, the subjects performed 3 continuous, maximal-effort jumps on a force plate (Advanced Mechanical Technology, Inc., Watertown, MA, USA; data analyzed with DartPower 2.0, Athletic Republic). The subjects kept their hands on the hips throughout the testing procedure to eliminate the role of the upper body arm movement on whole-body power production.

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Bench Throw Test

The Myotest bench throw test was completed as previously described (9) using a load of 30% of the subject's body mass (Myotest Inc., Durango, CO, USA). Briefly, the Myotest was attached to the bar of a Smith machine (LifeFitness, Schiller Park, IL, USA) while subjects adopted a supine position on a bench. Three maximal, discontinuous throws were completed at the 30% load while the Myotest was recording. Recording was initiated only after the bar was unracked and was stopped before reracking the bar.

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Plyo Press Power Quotient

The supine 3PQ is a validated measure of power output that has been shown to be as reliable and more sports-specific than the Wingate anaerobic test (29,33). The test consists of 30 seconds of continuous, maximal double-leg presses at 125% of body mass on a Plyo Press (Plyo Press 625 III, Frappier Acceleration, Fargo, ND, USA). The subjects were instructed to jump as high as they could in a maximal powerful action for each dynamic explosive leg press on the Plyo Press machine. Immediately before and after the 3PQ, heart rate, and the Borg CR-10 rating of perceived exertion (RPE) scale (5,30) were collected. (Perceptual scales of fatigue, soreness, headache pain, and anxiety were also assessed using 10-cm visual analog scales [10,24]; the scales were not significantly different between protocols and results are not reported here.)

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Statistical Analyses

The data are presented as mean ± SD. All data sets were examined for assumptions for linear statistics including normal distribution and homogeneity of variance and met all of the criteria for use of linear statistics. Test-retest reliability of the dependent variables in the testing sequence used demonstrated intraclass correlation coefficients of R ≥ 0.96. Statistical power was determined to be ≥0.91 for each dependent variable. These are important contexts for this investigation allowing robust analysis of potential treatment effects to be assessed. A 2-way analysis of variance (sex × treatment) was then used to analyze the data. When a significant F score resulted, Tukey post hoc tests were used to see where pairwise differences occurred. Significance in this study was set at p ≤ 0.05.

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Results

As shown in Figures 1 and 2, bench throw power and force under the PB MG condition were significantly higher in both men and women than for either the No MG or Reg MG conditions. This was in contrast to the fact that the Reg MG condition decreased bench throw power production below No MG in men. In the 3PQ, only men displayed increased power (Figure 3) and force (Figure 4) production while wearing the PB MG. Sex differences were demonstrated within each condition for both bench throw and 3PQ power and force measures.

Figure 1

Figure 1

Figure 2

Figure 2

Figure 3

Figure 3

Figure 4

Figure 4

Predictably, RPE increased in all conditions from pre-3PQ to post-3PQ, but neither RPE nor heart rate was significantly different between conditions (Table 1). Despite a lack of differences in physiological (heart rate) or perceptual (RPE) indices of exertion, men displayed significantly less percent power decrement over the course of the 3PQ test while wearing the PB MG performance mouth guard. This decrement was also significantly less than women experienced.

Table 1

Table 1

As shown in Table 2, there was a significant increase in rate of power production during the vertical jump for the PB MG protocol in men. There were no significant differences in peak power or vertical jump height despite favorable differences in magnitude. Significant sex differences were seen for all vertical jump indices.

Table 2

Table 2

In addition to the variables investigated for performance benefits, several variables were investigated to determine the span of potential benefits and to determine whether the PB MG would negatively impact any other physical performances. As shown in Table 3, no significant differences were demonstrated between conditions in 10-m sprint time, sit-and-reach distance, visual reaction time, or medial-lateral balance. Men were significantly faster than women in the 10-m sprint.

Table 3

Table 3

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Discussion

In general, the primary findings of this investigation were that under controlled laboratory conditions, a customized over-the-counter performance mouth guard positively impacts force and power production in power exercises. Furthermore, to the best of our knowledge, this is the first investigation into performance mouth guards and power production that has examined women as subjects (2,8). The PG MG showed no negative effects with its use in any of the experimental variables examined. With both upper and lower body power capabilities essential for sport and physical activities, such findings provide new insights into mouth guard use.

Although upper body strength has been described in a previous investigation (2), to the best of our knowledge, this is the first investigation to describe benefits for the use of a customized mouth guard upper-body power production (Figures 1 and 2). The benefits to upper body power production was an important and novel new observation observed for both sexes. The instantaneous explosive effort might well require not only breath holding but also a natural clenching of the teeth upon the performance of a concentric explosive push of the bar. Our study findings indicate that PB MG may well help in sports that require upper-body power in a loaded task and in sports not typically associated with mouth guard use such as basketball, striking, or throwing sports.

Our lower-body findings in men (Figures 3 and 4) are in agreement with those of the previous work describing increased Wingate power production (analogous to the 3PQ) with performance mouth guards (2,8). However, we appear to be the first to demonstrate that men when wearing the PB MG were better able to “sustain” power production performance over the course of the 3PQ test. This improved maintenance of power was achieved without increases in perceptual or physiological effort or strain and supports the concept that the construction of the mouth guard contributed to this effect (Table 1). A reduction in physiological strain with mouth guard use has been observed in prior human and studies and might have mitigated an increase in stress despite greater force and power production efforts arising from the contractile machinery in the neuromuscular system (8,14,37,38,46). In addition, as reviewed previously, the chewing or repetitive clenching of the teeth might have been differentially optimized with the customized PB MG during the repetitive high force and power efforts and is also a possible positive mediating factor that may have optimized jaw positioning and function.

Women did not benefit from the performance mouth guard in lower-body power tasks in this study. The underlying reasons for this sex difference with lower body power production remains speculative and might be related to differential use of mouth guard (e.g., bite down or clenching of teeth or not) during the tests.

Clenching of the teeth during a high force or power activity may optimize performances (11,20). Ebben et al. (11) had previously demonstrated that “clenching” increased rate of force development in the vertical jump exercise and decreased time to peak force in men and women without altering peak force. Hiroshi (20) also saw an increased rate of force production during maximal grip strength testing with teeth clenching. In this study, we also demonstrated an increased rate of power development in men for the vertical jump with the use of a PB MG mouth guard yet peak power was not affected (Table 2). It might be speculated that a mouthguard that optimizes jaw positioning when teeth are clenched may optimize power production and rate of force production. Based on the prior studies of Ebben et al. (11) and Hiroshi (20), it might be speculated that optimal clenching of teeth with the PB MG allowed this more rapid rate of power development and more sustained power maintenance. This increase in power may be of importance because it relates to a variety of tasks and sport skills such as reduced time on the ground and getting more rapidly getting off the ground to grab a rebound in basketball or jump to block a shot in volleyball.

It has been shown that rate of force development and force in grip strength is enhanced with teeth clenching (20). How each subject used (e.g., clench or bite down or not), the mouth guard in this study was not directly determined nor was it coached before any testing. All subjects were allowed to do what came naturally for them during each test when using each of the mouth guards. The same can be said for the no-mouth guard control condition. It may well be that optimization of jaw structures with the use of the customized PB MB allows for more optimal spacing and orientations when teeth clenching does occur. In power type activities, teeth clenching may be used upon the initiation of the rapid force needed for the activity. With the higher power output found in the upper body with a multiple trails in the bench throw test and with repeated efforts in the 3PQ test, a more optimal jaw spacing with the use of the PB MG may appear to allow a more natural teeth clenching activity that may have mediated the positive outcomes in these tests. A novel thought is that it may have also created a stability or a more optimal pivot point from the orientation of the head for instantaneous focusing and impact timing of exertion for optimal power output. Thus, the differential design of the mouth guards may influence and optimize anatomical orientations of the jaw, thereby improving physical performance.

A number of prior investigations reported athlete concerns that mouth guard use could result in performance detriment of some kind (6,8,12,34,44). Interestingly, this negative effect was observed for the Reg MG in upper body bench throw power production, which was lower than the No MG in men. Additionally, our investigation also tested a wide range of other performance parameters, including acceleration (10-m sprint time), balance, visual reaction time, vertical jump performance, and flexibility to determine if any other physical performance was affected by use of a mouth guard. Although mouth guard use has been shown to significantly decrease auditory switch-response reaction time in 1 study (17), it did not impact visual reaction time in this study as demonstrated by a lack of any negative effects in the Quickboard visual reaction time test. In agreement with previous work, we also did not observe changes in sprint time or vertical jump height (8). Indeed, no performance decrements were seen in any of these parameters with the use of a performance mouth guard that benefits power performance components (Table 3). This suggests that although a regular mouth guard could cause mild decrements to certain types of athletic performance, athletes wearing the customized performance mouth guard investigated here would not be negatively affected in any other crucial physical performance parameter.

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Practical Applications

As previously described, many athletes, even including recreational athletes, may be wary of mouth guards because of a perceived decrement to performance. The lack of performance decrements in this investigation across a wide range of parameters should encourage athletes to wear the performance mouth guard during any sport not only for protection but also for potential benefits related to power production. Although this investigation did not examine any one sport's activity, the mouth guard may benefit any male or female athlete involved in power sports where the upper body is important to performance. In addition, it may be of interest to any male athlete involved in repetitive lower-body power-intensive sports particularly because the customized mouth guard helped to sustain lower-body repetitive power performance in men. Thus, the customized PB MG appears to offer more than just protection from its use with the initial findings from this investigation.

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Acknowledgments

The funding for this investigation was provided by Power Balance LLC, Laguna Niguel, CA. The authors also wish to thank The Quick Board, LLC, Memphis, TN, for the Quick Board and Frappier Acceleration, Fargo, ND, for the Plyo Press. They would like to thank their subjects for their dedicated participation and their laboratory assistants and medical staff for the support of this investigation. This was an independent investigation, and the results of this study do not constitute endorsement of the product by the National Strength and Conditioning Association.

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Keywords:

power endurance; speed; visual reaction time; rate of power production

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