Sport involvement, particularly contact sport, has a relatively high risk of injury (1,2,18,21,24). Men have particularly higher rates of injuries as compared to women as a result of more choices of contact team sports (i.e., football and wrestling) available to men (2). With the removal of nonequivalent male contact sports to female contact sports, there are no differences between male and female injury risk rates (2). Types of injuries and degree of injuries vary depending on extent of protection use. Mouthguards are the most commonly used form for dental injury protection (20). Dental injury rates decrease with the use of a mouthguard, and the lowest rates of dental injuries occur when mouthguard use is mandatory (12,23).
Some athletes do not use a mouthguard despite the known decline in dental injuries with their use. The 3 main reasons why some athletes choose not to wear mouthguards are because of (a) discomfort, (b) speech impairment, and (c) the belief that there are negative breathing effects associated with mouthguard use (3,6,7,11). The same motives for choosing not to use a mouthguard have been reported for men and women (3,6,7,11). It has been shown, with different types of mouthguards, that airflow and oxygen consumption (VO2) are not significantly decreased during low-intensity exercise (8,13,17). Conflicting results have been shown at high-intensity exercise (5,8,13,17). At maximal exercise intensity, Francis and Brasher (13) and Delaney and Montgomery (8) found significantly lower maximum oxygen consumption (O2max) and peak minute ventilation (E) with the use of a mouthguard versus nonuse. Others (5,17) found no significant differences in O2max and peak E when comparing mouthguard use versus nonuse.
At a given intensity, O2, VE, and heart rate (HR) were found to be higher in men than in women (14,16). Studies have also concluded that women consume more oxygen at a given submaximal exercise intensity than men when O2 is normalized by body mass (16) and that women are limited during heavy exercise as a result of pulmonary structural differences (15). Thus, there are O2, E, and HR differences between men and women during exercise, and these differences may be affected by mouthguard use. Several mouthguards have been studied; however, there are no known studies with the LoPro Femä mouthguard, a boil-and-bite mouthguard specifically made for women. It is claimed this mouthguard offers a better fit for female athletes because of the use of different thermoplastics in its manufacturing (i.e., a melting point lower than standard mouthguards to allow for a better and more comfortable fit for women). Therefore, the purpose of this study was to examine O2, HR, E, respiratory exchange ratio (RER), and rating of perceived exertion (RPE) during submaximal and maximal exercise in college-aged women with and without the use of a universal self-adapted (boil-and-bite) mouthguard and a female-specific boil-and-bite mouthguard.
Experimental Approach to the Problem
The repeated-measures study design protocol examined O2, HR, E, RER, and RPE during exercise with and without the use of mouthguards, including a mouthguard made specifically for female athletes. A regular boil-and-bite mouthguard was also examined to compare results with the female-marketed mouthguard.
Subjects included 11 college-aged women (age: 22 ± 3.3 y; height: 159.8 ± 4.3 cm; body mass: 63.7 ± 8.9 kg). Exclusion criteria included smokers and those with a history of cardiorespiratory problems, temporomandibular joint disorders, asthma, dentures, or braces to prevent confounding variables on cardiorespiratory measures. All procedures were approved by the University Institutional Review Board for Human Subjects and each subject read and signed an informed consent prior to any testing.
Two types of mouthguards were used. The first type was a self-adapted (boil-and-bite) mouthguard (self-adapteduniv; MuellerGuard, Prairie du Sac, WI, USA) that could be bought at sporting goods stores and can be used by both men and women (Figure 1). The second type was a self-adapted mouthguard (self-adaptedfemale; Brain-Pad LoPro Female, Conshohocken, PA, USA) specifically marketed to female athletes (Figure 2). Both mouthguards were fitted by following the manufacturer's instructions. This required the subjects to dip the mouthguard into hot water and bite into it to create a more custom fit. The self-adapteduniv was placed in boiling water for 30 s and positioned on the maxillary (upper) jaw. The subject then bit down and used their tongue to mold the mouthguard to their mouth. The mouthguard was set by running it under cold water. The self-adaptedfemale was fit over the lower teeth and cut to proper length. A bite stick inserted into the self-adaptedfemale and the mouthguard was placed in boiling water for 30 s. The self-adaptedfemale was placed over the mandibular (lower) jaw and the subject bit down to mold the mouthguard to their teeth and gums using their fingers and tongue. The self-adaptedfemale was also set by running under cold water. In addition to the self-adapteduniv and self-adaptedfemale mouthguards, each participant underwent testing without a mouthguard (NO).
Maximal Cycle Ergometer Test
Each subject visited the lab on 3 separate occasions separated by an average of 9.1 ± 6.3 days. During each visit, subjects performed a maximal cycle ergometer (Monark Ergomedic 839 E, Monark Exercise AB, Varburg, Sweden) test to exhaustion for the measurement of O2 to max (O2max), E, and RER. Seat height was adjusted so that the subject's legs were near full extension during each pedal revolution. After a period of stabilization at rest, the subject began pedaling at 50 W for 5 min. The power output was then increased by 30 W every 2 min until exhaustion and O2max were reached. Expired air was collected throughout the test using an open-circuit spirometry (Parvo Medics metabolic cart, model 2400, Sandy, UT, USA). A Hans Rudolph full face mask was used during all exercise tests to accommodate the use of a mouthguard. Heart rate was monitored 30 s prior to the next increase in exercise intensity and just before the end of the test using a Polar heart rate monitor (Polar Electro, Inc., Lake Success, NY). Each subject rated their RPE 30 s prior to the next increase in exercise intensity using Borg's rating of perceived exertion scale (4). More specifically, subjects rated their overall degree of exercise exertion on a scale ranging from 6 (“No exertion at all”) to 20 (“Maximal exertion”). O2max was defined as the highest O2 value in the last 30 s of the test if the subject met at least 2 of the following 3 criteria: (a) 90% of age-predicted heart rate (220 − age), (b) respiratory exchange ratio >1.20, and (c) a plateauing of oxygen uptake (≤150 ml/min−1 in O2 over the last 30s of the test) (19). Subjects performed the maximal cycle ergometer tests under 3 conditions: (a) using the self-adapteduniv mouthguard, (b) using the self-adaptedfemale mouthguard, or (c) using no mouthguard. The order of testing for these conditions was randomly determined.
Five separate 3 × 3 mouthguard (self-adapteduniv, self-adapatedfemale, NO) × power level (80, 110, and max W), repeated-measures analyses of variance (ANOVAs) were used to compare differences in O2, HR, E, RER, and RPE. Differences were considered significant at p ≤ 0.05. Significant interactions were followed up with 3 separate repeated-measures ANOVAs for each mouthguard condition. Based on previous studies, a priori analyses were used to determine sample sizes that yielded power values of 0.90 or greater for the dependent variables.
Heart Rate (HR)
There was no significant 2-way interaction (power level by mouthguard) with HR; however, there was a significant main effect for power level (HR at 80W was less than 110W, HR at 80W was less than max, and HR at 110W was less than max) (Figure 3).
Rating of Perceived Exertion
There was no significant 2-way interaction (power level by mouthguard) with RPE; however, there was a significant main effect for power level (RPE at 80W was less than 110W, RPE at 80W was less than max, and RPE at 110W was less than max) (Figure 4).
There was no significant 2-way interaction (power level by mouthguard) with O2; however, there was a significant main effect for power level (O2 at 80W was less than 110W, O2 at 80W was less than max, and O2 at 110W was less than max) (Figure 5).
There was a significant 2-way interaction (power level by mouthguard) with E. Follow-up repeated-measures ANOVAs indicated that ventilation increased greater from 110W to max with the no-mouthguard condition than for self-adapteduniv and self-adaptedfemale conditions. However, there was no significant difference in E between mouthguards at any given power level (Figure 6).
Respiratory Exchange Ratio
There was a significant 2-way interaction (power level by mouthguard) with RER. Follow-up repeated-measures ANOVAs indicated that RER increased greater from 110W to max with the no mouthguard condition than for self-adapteduniv and self-adaptedfemale conditions. However, there was no significant difference in RER between mouthguards at any given power level (Figure 7).
The results of the present study indicated the mouthguard condition did not affect HR response at a given power level. These results were similar to those reported by others (8,17), although there were differences in the types of mouthguards used in the studies. Keçeci et al (17) used a custom made mouthguard and Delaney and Montgomery (8) used the WIPSS Jaw-Joint Protector boil-and-bite mouthguard. Nonetheless, the results of the present study support the findings of others that the HR response to exercise is not affected by mouthguard use. The results did indicate that there was a significant increase in heart rate with increases in power level, as expected. The more intense the activity, the harder and faster the heartbeats. The heart must work harder with a greater work load to meet the demands for the increased need for more blood and oxygen by the working skeletal muscles.
Similar to HR, the study indicated that RPE was not affected with the mouthguard conditions at any given power level. These results are consistent with the findings of Bourdin et al (5), which were that there were no significant difference for RPE at maximal exercise for all mouthguard types that were tested. RPE increased with an increase in power level. Borg's rate of perceived exertion scale has been found to be correlated with heart rate (4,22). Therefore, because HR increased with power level, RPE was expected to increase also. The increased power level forced the subject to work harder, regardless of mouthguard use. Because the subject worked harder at each power level, the RPE increased with the increased power level from submaximal to maximal levels.
The current study identified no significant difference in O2 or O2max between mouthguard conditions. Keçeci et al (17) and Bourdin et al (5) reported similar results indicating that O2 and O2max were not affected by mouthguard use. Delaney and Montgomery (8) and Francis and Brasher (13), however, suggested that although mouthguards had no affect on O2 at submaximal power levels, O2max decreased with mouthguard use. Francis and Brasher (13) used a much bulkier bimaxillary mouthguard. The larger mouthguards could have prevented oxygen uptake at maximal power levels, thus resulting in a lower O2max as compared to no mouthguard or a smaller mouthguard, as used in the present study.
The conflicting results between Delaney and Montgomery (8) and the current study may have been a result of the training level of the subjects used. For example, it has been found that approximately 50% of highly trained elite athletes experience hypoxia at maximal exercise levels (9,10). Hypoxia in highly trained athletes can be attributed to the shorter cardiopulmonary transit time resulting in blood circulating faster through the system with lower amounts of oxygen (10). Hypoxia in elite athletes may also result from respiratory muscle fatigue. The current study used untrained subjects (average O2max = 30.99 ± 6.69 ml/kg−1/min−1) and were thus unlikely to experience hypoxia.
The results of the current study indicated mouthguard use did not hinder ventilation at any power level. These results compare with those reported by Delaney and Montgomery (8), Keçeci et al (17), Bourdin et al (5), and Francis and Brasher (13) at submaximal power levels. These studies similarly found no differences in E at submaximal power levels when comparing mouthguard use to no mouthguard use. These results are also similar to those of Keçeci et al (17) and Bourdin et al (5), who found no differences in Emax. However, these results are in conflict with the findings of Delaney and Montgomery (8) and Francis and Brasher (13), who claim significant decreases in Emax with mouthguard use. The current study also showed no significant effect on E at any given power level, even though ventilation increased more for the no mouthguard group from 110 W to max W as compared to either of the mouthguard conditions. Further evidence that ventilation was not affected at any given power level by the different mouthguard conditions in the present study is that O2 and O2max were not affected by mouthguard use. Mouthguards also may not have affected ventilation at any given power level because of the ability for the subject to compensate through nose breathing.
One of the main reasons that some athletes have chosen not to wear mouthguards is because the athletes feel that a mouthguard obstructs breathing. Delaney and Montgomery (8) distributed a 10-point-scale questionnaire that included subjectivity of a mouthguard hindering breathing. The average score was a 3.6, indicating that the subjects felt that mouthguard use moderately hindered breathing during the treadmill skating sessions. The current study did not confirm a hindrance in ventilation with mouthguard use at any given power level. The conflicting results in the current study and prior studies suggest there may be some psychological bearing on perceived ventilation with the use of a mouthguard, the types of mouthguards used in these studies had differential effects on ventilation, or some other unidentified mechanism.
The results of the study indicated that there was no difference in RER at any power level when comparing mouthguard conditions. One study examined RER with the use of a mouthguard during exercise. Similar to the current study, Keçeci et al (17) found no difference in maximum RER in subjects with and without a mouthguard. However, like E, there was a greater increase in RER from 110W to maximum in the no mouthguard condition versus both mouthguard conditions. This would be expected after analyzing E because, with the greater increase in ventilation with no mouthguard use, CO2 expiration would also have a greater increase from 110W to maximum, resulting in a greater increase in RER with the no mouthguard condition.
The results of the study indicated that the universal self-adapted mouthguard and female-specific self-adapted mouthguard did not affect the physiological variables of heart rate, rating of perceived exertion, minute ventilation, oxygen consumption, or respiratory exchange ratio at any given power level during submaximal and maximal exercise in women. Furthermore, there were no differences between mouthguards despite the fact that self-adaptedfemale was made specifically for women, whereas self-adapteduniv was for both male and female use. Further examination between trained and untrained athletes and mouthguard use would be advantageous because prior studies (5,8,17) all used trained subjects and some reported conflicting results with the current study.
To increase mouthguard use among athletes, this study can be provided as evidence that mouthguard use does not hinder physiological variables or the perception of exercise difficulty during aerobic exercise performance. Athletes can be encouraged to wear mouthguards without fear of decreased aerobic performance. In addition, the results suggest that the aerobic recovery period between anaerobic work intervals in sports such as basketball and football will not be hindered by mouthguard use.
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