Ergogenic benefits of carbohydrate mouth rinsing on endurance exercise performance

Harris Kamal Kamaruddin; Al Hafiz Abu Bakar; Ahmad Munir Che Muhamed

doi:10.4103/mohe.mohe_36_22

REVIEW ARTICLE

Year : 2022 | Volume : 11 | Issue : 2 | Page : 51-56

Ergogenic benefits of carbohydrate mouth rinsing on endurance exercise performance

Harris Kamal Kamaruddin¹, Al Hafiz Abu Bakar¹, Ahmad Munir Che Muhamed²
¹ Faculty of Sports Science and Recreation, Universiti Teknologi MARA, Cawangan Perlis, Kampus Arau, Perlis, Malaysia
² Department of Community Health, Advanced Medical and Dental Institute, Universiti Sains Malaysia, Kepala Batas, Penang, Malaysia

Date of Submission	24-Dec-2022
Date of Decision	27-Dec-2022
Date of Acceptance	28-Dec-2022
Date of Web Publication	22-Feb-2023

Correspondence Address:
Ahmad Munir Che Muhamed
Department of Community Health, Advanced Medical and Dental Institute, Universiti Sains Malaysia, Kepala Batas, Penang
Malaysia

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/mohe.mohe_36_22

Abstract

Carbohydrate ingestion during exercise has been extensively investigated to enhance exercise performance, particularly during prolonged exercise (>2 h) when endogenous carbohydrate is limited. The pertinent benefit of carbohydrate ingestion is that it delays the depletion of vital energy source for exercise, hence delaying fatigue. Athletes have often been advised to drink or rehydrate (replace body fluid loss) to ensure sufficient energy source and to avoid dehydration during exercise Nevertheless, the ability for athletes to rehydrate in a real race setting, maybe challenging due to fluid availability and the nature of the event, such as during a running event. As an alternative to drinking, carbohydrate mouth rinsing has resulted in enhanced prolonged exercise performance. The underlying mechanism responsible for this improvement has been associated with the activation of the oral receptor that is related to reward and behavioural centre of the brain that contributed to enhancing exercise performance. Numerous studies have examined factors that influence the effectiveness of carbohydrate mouth rinsing. While these studies have presented convincing evidence to support their hypothesis, future studies are required to provide new insight into the effectiveness of carbohydrate mouth rinsing on exercise performance. These questions include how the environmental condition and dehydration level may influence the effectiveness of carbohydrate mouth rinsing on endurance exercise performance.

Keywords: Carbohydrate solution, endurance exercise mouth rinsing

How to cite this article:
Kamaruddin HK, Bakar AH, Muhamed AM. Ergogenic benefits of carbohydrate mouth rinsing on endurance exercise performance. Malays J Mov Health Exerc 2022;11:51-6

How to cite this URL:
Kamaruddin HK, Bakar AH, Muhamed AM. Ergogenic benefits of carbohydrate mouth rinsing on endurance exercise performance. Malays J Mov Health Exerc [serial online] 2022 [cited 2023 Sep 25];11:51-6. Available from: http://www.mohejournal.org/text.asp?2022/11/2/51/370244

Introduction

Carbohydrate intake before, during and after exercise has been widely shown to have a positive effect on endurance exercise performance (Rothschild et al., 2020; Jeukendrup et al., 1997; Below et al., 1995; Anantaraman et al., 1995). As an important energy substrate, carbohydrate source of intake by athletes is influenced by its taste through oral sensory. Within the last decade, the practice of mouth rinsing carbohydrate solution has gained popularity among physically active individuals, with the belief that rinsing a carbohydrate solution may enhance their endurance exercise capacity by elevating their drive and motivation to exercise. The practice of carbohydrate mouth rinsing involves flushing a carbohydrate solution around the oral cavity for a short period and followed by expulsing the solution. This review will systematically discuss the ergogenic benefits of carbohydrate mouth rinse on endurance exercise performance and factors associated with the improvement in endurance exercise performance.

Carbohydrate Mouth Rinsing and Endurance Exercise Performance

The study by Carter et al. (2004) initiated the notion that the route of the administration of exogenous CHO is necessary to enhance exercise performance that lasts for about an hour. In their initial study, the cyclists rinsed their mouth intermittently with 6.4% maltodextrin solutions or plain water (PLA) for 5 s during 40 km time trial cycling performance. As a result, a significant 2.9% decrease in time trial was noted for CHO mouth rinse solution, when compared to that with PLA. The author added that the mechanism to these exercise improvements was likely due to the incorporation of exogenous CHO to increase the central drive or motivation without altering the metabolic cause (Carter et al., 2004).

Since the novel finding revealed by Carter et al. (2004), many researchers have reported similar outcomes. Rollo et al. (2008) reported that the ergogenic effect of 6% CHO mouth rinse solution improved the overall distance covered during self-selected 30 min run in contrast with the same colour and taste that matched the PLA. This study displayed the effects of CHO mouth rinse during 30 min of running exercise. Nevertheless, this study was not a performance study. Instead, the participants were required to run on a motorised treadmill at a speed that had an equivalent rating perceived exertion (RPE) of 15. The authors assessed the participants' subjective feeling, self-selected speed and total distance during the exercise. The improvement in exercise time and distance had been related to the enhanced feeling of pleasure when performing CHO mouth rinse. Similarly, Rollo and Williams (2010) evaluated the benefits of carbohydrate-electrolyte (CHO-e) mouth rinsing during 60 min running performance. The treadmill was modified for the participants to change their running speed without the need for manual input or visual feedback from the runners. The results showed that those who rinsed with CHO-e achieved more running distance (14298 ± 732 m) with a significant enhancement of 1.5% from colour and taste that matched PLA.

Chambers et al. (2009) assessed the effects of CHO containing glucose and/or maltodextrin for 1 h time trial cycling. The trained cyclists performed exercise at 75% of maximal work for an hour in three varying situations: 6.4% glucose, 6.4% maltodextrin and PLA mouth rinse. The mouth rinse duration was initiated for 10 s, while the solution was rinsed at every 12.5% of the trial completed. The study revealed that exercise with glucose and/or maltodextrin mouth rinse solutions led to improvement of 2%–3% in the time trial and average power when compared to PLA. The study also revealed no variance in cycling performance between CHO-containing solutions.

Further evidence for the performance-enhancing effects of CHO mouth rinse was provided by Pottier et al. (2010). The subjects of the study performed high-intensity cycling exercises for 1 h time trial with mouth rinse or ingestion of either a 6.4% CHO-e solution or PLA before and throughout the time trial. As for the mouth rinse condition, time performance was recorded faster in CHO mouth rinse (61.7 ± 5.1 min) than that with PLA (64.1 ± 6.5 min). Improvement in performance linked with CHO mouth rinse has been speculated as fatigue signals from the muscle to the brain are suppressed unconsciously by afferent CHO signals from the CHO receptors in the mouth to parts of the brain (Pottier et al., 2010).

Since then, a substantial number of studies have revealed that the practice of CHO mouth rinse did improve cycling performance (Beaven et al., 2013; Che Muhamed et al., 2014; Devenney et al., 2016; Fares and Kayser, 2011; Murray et al., 2018; Pires et al., 2018) and running performance (Fraga et al., 2015; Konishi et al., 2017; Rollo and Williams, 2010; Rollo et al., 2008). Despite the positive performance changes associated with CHO mouth rinse, some other studies failed to report enhancement in exercise performance (Ali et al., 2016; Arnaoutis et al., 2012; Beelen et al., 2009; Ispoglou et al., 2015; Kulaksiz et al., 2016; Trommelen et al., 2015; Watson et al., 2010). Trommelen et al. (2015), for example, assessed the impact of CHO mouth rinse (sucrose) on a 1 h cycling time trial in both post-absorptive and post-prandial conditions. The study revealed no improvement in exercise performance following mouth rinsing with sucrose, as compared with PLA during exercise among well-trained cyclists. They speculated that the artificial sweetener aspartame was bound to the mouth's taste receptor cells (TRCs) and concealed the potential ergogenic effects of the CHO mouth rinse. Similarly, Ali et al. (2016) found that rinsing with sucrose and maltodextrin had neither ergogenic effect nor changes in endocrine or metabolic responses to PLA.

Underlying Mechanism For Mouth Rinsing On Brain Activation

The enhanced endurance exercise performance with CHO ingestion had been speculated due to non-metabolic factors. According to Carter et al. (2004), the mechanics linked to enhanced exercise performance with CHO mouth rinse is still unknown. Nonetheless, the author speculated that it might involve CHO receptors in the oral cavity modulating central pathways related to motivation. It is believed that the central effect of CHO on exercise performance could function through activation of receptors linked to the brain (Carter et al., 2004).

In seeking the mechanisms to explain the central effects on exercise performance, Chambers et al. (2009) used fMRI to identify areas of the brain activated with CHO mouth rinse. The authors used glucose and/or maltodextrin solution for mouth rinse on well-trained cyclists performing in a 1 h cycle time trial (75% of maximal work). The study revealed that tasting sweet glucose and non-sweet maltodextrin CHO solutions activated various brain regions, such as the ventral striatum and anterior cingulate cortex, in which these activations were unresponsive to artificial sweetener saccharin. The fMRI evaluation showed that CHO mouth rinse activated supraspinal pathways of the brain linked with motivation and reward during exercise (Chambers et al., 2009). The activation of the anterior cingulate cortex created a positive afferent signal to the body that may minimise perceived effort during exercise, hence allowing the cyclist to produce a higher work rate for the same RPE. A similar higher self-selected running speeds during 30 min run at RPE corresponded to runners who experienced enhanced pleasure after rinsing their mouth with CHO (Rollo et al., 2008). Brain activation due to CHO mouth rinse was likely to decrease in the subjective perception of effort during exercise (Carter et al., 2004; Dolan et al., 2017). These results have proven the function of CHO mouth rinse during exercise performance, which could be a possible mechanism in enhancing exercise performance.

Interestingly, Chambers et al. (2009) reported that the neural response did not occur to sweet but non-caloric saccharin. The sweet non-caloric artificial sweeteners were detected as sweet by cyclists, however, failed to activate the same brain area as glucose and maltodextrin did. This suggests that a class of TRCs, yet unidentified receptors that, respond to the amount of caloric content independently to the level of sweetness. Hence, the caloric property of CHO solution may be the key reason that activates various brain activation, including enhancing exercise performance (Chambers et al., 2009).

Another important finding related to CHO mouth rinsing refers to the ability in counteracting the adverse effect of muscular fatigue during exhaustive exercise (Jeffers et al., 2015; Pottier et al., 2010; St Clair Gibson et al., 2001). Jeffers et al. (2015) used electromyography (EMG) and transcranial magnetic stimulation to investigate the effects of CHO (maltodextrin) and PLA mouth rinse on time trial cycling performance and mechanism of fatigue. Despite obtaining an insignificant variance for time trial performance between CHO and PLA mouth rinse, the authors revealed that CHO mouth rinse attenuated neuromuscular fatigue that ascertained high-intensity cycling. They elaborated that CHO mouth rinse produced less fatigue experience during time trial, which could be translated to attenuated neuromuscular fatigue during fatiguing exercise. Similarly, Bailey et al. (2019) observed that CHO mouth rinse amplified the magnitude of corticospinal motor excitability and lower limb muscle performance at the early stage of maximal voluntary contractions (MVC). In summary, the CHO mouth rinse increased the activation of neural pathways that reduced RPE, reward perception and corticospinal excitability (Bailey et al., 2019).

Meanwhile, Jensen et al. (2014) investigated the effect of CHO mouth rinse on neuromuscular fatigue during cycling exercise and revealed that decreased torque attenuation in fatiguing exercise bout with CHO mouth rinse when compared to non-caloric control. The authors suggested that the repetitive act of CHO mouth rinse during preload exercise led to less fatigue experience amidst the cyclists and maintained a peripheral neural transmission that allowed the motoneurons to receive more input and to attenuate the development of global fatigue (Jensen et al., 2014). Bastos-Silva et al. (2016) reported a reduction in EMG activity during moderate-intensity cycling exercise for PLA condition. However, the reduction in EMG for CHO mouth rinse was greater when compared to PLA at 30 min and at the end of the exercise, signifying that the effect of CHO mouth rinse is more significant in fatigued muscle (Bastos-Silva et al., 2016). Moreover, CHO mouth rinse has been shown to amplified corticospinal motor excitability at the quadriceps muscle during MVC exercise (Bailey et al., 2019).

Mouth Rinse: Other Than Carbohydrate Solution

Several studies have evaluated the effects of various types of mouth rinsing solutions during exercise performance (Beaven et al., 2013; Kasper et al., 2015; Mundel and Jones, 2010). Mundel and Jones (2010) investigated if menthol solution mouth rinse would increase the endurance capacity in time to exhaustion (TTE) cycling exercise. The results showed that subjects who rinsed their mouth with menthol solution improved their exercise duration by 9%, most likely due to the stimulation of oropharyngeal cold receptors by menthol.

Apart from menthol mouth rinse, caffeine ingestion is also believed to involve the central modulation of motor unit activity and adenosine receptor antagonism (Kalmar, 2005). Beaven et al. (2013) used caffeine mouth rinse on repeated maximal sprint efforts and found that it enhanced power production and rapidly improved maximal exercise performance. Likewise, caffeine mouth rinse improved 30 min arm cranking performance by mediating the increase in cadence and power output (Sinclair et al., 2014). Kizzi et al. (2016) revealed that caffeine mouth rinses increased peak power output during repeated cycling sprint bout when compared to CHO. Caffeine mouth rinse could enhance performance during high-interval running when compared to PLA (Kasper et al., 2015). Meanwhile, guarana mouth rinses improved cognitive functions and decreased subjective perception of effort during submaximal cycling exercise (Pomportes et al., 2017).

Nevertheless, several observations seemed to suggest that caffeine mouth rinse might not be beneficial in enhancing exercise performance. Clarke et al. (2015) revealed that caffeine alone or a mixture with CHO mouth rinse displayed insignificant effects on maximum strength or muscular endurance performance. A possible reason for this outcome during the exercise protocol could be that exercise intensity elicits near maximal RPE and heart values, which create a 'ceiling effect' that makes any appreciable variances between the conditions extremely difficult to be distinguished (Beaven et al., 2013; Rossato et al., 2019).

Factors That Influence The Effectiveness Of Mouth Rinse

Mouth rinse duration

The optimal duration to perform mouth rinsing was examined by Sinclair et al., (2014), where they found that mouth rinsing a 6.4% CHO for 10 s significantly improved a 30 min self-selected cycling performance when compared to rinsing the same solution for 5 s. Sinclair et al., (2014) concluded that the improvement in exercise performance when mouth rinsing a CHO solution for 10 s as compared to 5 s would suggest a dose-response relationship to the duration of mouth rinse.

Improvement in exercise performance with 10 s duration of mouth rinse motivated several researchers to apply this regime in their studies (Chambers et al., 2009; Fraga et al., 2015; Kasper et al., 2015; Lane et al., 2013). Although the finding reported by Sinclair et al. (2014) promotes the use of 10 s mouth rinse duration during 30 min cycling event, this may be impractical during the competition that demands a higher breathing rate. During high-intensity events, the 5 s duration of mouth rinse appeared to be a more practical strategy than that of 10 s, as breathing could be potentially inhibited while rinsing the solution around the mouth (Sinclair et al., 2014). As such, many researchers have continued to practice 5 s mouth rinse duration in their studies (Arnaoutis et al., 2012; Carter et al., 2004; Che Muhamed et al., 2014; Jeffers et al., 2015; Rollo and Williams, 2010; Trommelen et al., 2015; Watson et al., 2010; Whitham and McKinney, 2007; Wright and Davison, 2013).

Fed And Fasted States

The discrepancy reported for positive and nil effects of CHO mouth rinse on high-intensity exercise endurance is influenced by pre-exercise meal (Jeukendrup et al., 2013). Most studies reported the beneficial effects on commencing exercise following an overnight fast (Chambers et al., 2009; Che Muhamed et al., 2014; Fares and Kayser, 2011; Rollo et al., 2008) or to be in a post-prandial state for up to 4 h (Carter et al., 2004; Devenney et al., 2016; Gam et al., 2013; Pottier et al., 2010; Rollo et al., 2011) One reason for studies to fail to determine the ergogenic effect of CHO mouth rinse is that the subjects received CHO pre-meal 2–3 h before exercise (Beelen et al., 2009). Ispoglou et al. (2015) discovered zero effect of CHO mouth rinse at post-prandial state despite rinsing with higher CHO concentrations. Comparable findings also have reported the nil effect of CHO feeding during high-intensity running and cycling exercises following the consumption of CHO-rich meal hours before the events (Rollo and Williams, 2010).

It is likely that the influence of the pre-exercise fasting period may affect the neural response to an oral stimulus. Rinsing a CHO solution following an overnight fast (12 h) has been shown to activate a higher level of activation within the brain regions, including the ventral striatum, amygdala and hypothalamus, as compared with ingestion of a 700 kcal liquid meal (Haase et al., 2009). These central responses are capable of modifying motor output, which might be dependent on the pre-exercise nutritional state.

The effectiveness of CHO mouth rinse in fasted or fed state, however, may not be a definitive regulator in enhancing exercise performance. A study by Whitham and McKinney (2007) showed nil ergogenic effect of CHO mouth rinse on subjects who fasted overnight following time trial running, while Pottier et al. (2010) observed enhanced performance with CHO mouth rinsing despite a meal 2 h before exercise. In fact, three studies directly addressed the impacts of fed and fasted states on exercise performance with CHO mouth rinsing (Fares and Kayser, 2011; Lane et al., 2013; Trommelen et al., 2015). A significant improvement effect on TTE at 60% maximal workload was recorded in both fed and fasted states, with 3.5% and 11.6% performance improvement, respectively (Fares and Kayser, 2011; Lane et al., 2013). Lane et al. (2013) revealed similar findings on investigating fed and fasted athletes following 1 h cycle time trial performance with maltodextrin and PLA. Performance benefits were reported in both conditions. However, the magnitude of improvement was significantly greater amongst those who fasted (3.3%) in comparison to those with the fed state (1.8%). However, previous study did not show any positive effect of CHO mouth rinse on both fasted and fed states following 1 h cycling time trial performance (Trommelen et al., 2015). To date, the consensus on this matter has been that carbohydrate mouth rinsing is more effective when commencing exercise following an overnight fast..

Environmental Condition: Level Of Heat Stress

The potential effect of CHO mouth rinse on endurance exercise performance during heat-stress environments has not been extensively analysed. A study by Che Muhammed et al. (2013) showed no additional variance in power output between CHO-e and PLA mouth rinse during 10 km time trial cycling in heat stress conditions (32°C and 75% relative humidity). Mouth rinsing with either CHO or PLA solution offered ergogenic benefits when compared to no-rinse condition. Similarly, Watson et al. (2014) revealed that CHO mouth rinse failed to increase time trial cycling performance in 30°C heat stress condition, while Cramer et al. (2015) demonstrated performance stagnant during 40 km self-paced cycling in the heat (35°C and 60% relative humidity). As a result, time and mean power output was similar between CHO and PLA trials, suggesting CHO mouth rinse failing to improve 1 h trial performance in hot and humid conditions (Cramer et al., 2015).

The reason for the diminished effectiveness of CHO mouth rinse on performance in heat environment has remained unclear (Watson et al., 2014). The presence of heat stress may mask or override signals from CHO receptors in the mouth, hence blunting any potential beneficial performance effect (Watson et al., 2014). Another reason refers to the high degree of thermal and cardiovascular strain, particularly towards the end of the time trial that may have completely mitigated any possible ergogenic effect of CHO mouth rinse (Cramer et al., 2015).

Hydration Status

The study by Arnaoutis et al. (2012) was the earliest to investigate the effect of plain water mouth rinse on dehydrated subjects in cycling exercise performance. Participants in the study by Arnaoutis et al. (2012) performed cycling exercises at 75% of their maximum power output to exhaustion while experiencing a 2% body water loss. The results indicated that mouth rinse intervention did not improve TTE cycling exercise among the dehydrated subjects when compared to water ingestion intervention. The authors speculated that lack of swallowing sensation and cool sense in the digestive tract as the reasons for the lack of performance improvement in the mouth rinse intervention (Arnaoutis et al., 2012).

A more recent study by Kamaruddin et al. (2019) reported an ergogenic benefit of CHO mouth rinsing significantly improved endurance running performance (~1) among well-trained subjects while experiencing dehydration. The improvement in running performance reported by Kamaruddin et al. (2019) was when well-trained athletes experienced up to ~4.5% body mass loss. The pronounced improvement in mouth rinsing while being in a dehydrated state was likely due to the oral senses becoming more sensitive to the presence of CHO. It was postulated that the improved exercise performance in the dehydrated state was largely due to the individual's oral senses becoming more responsive to the calorie-containing CHO solutions, as was previously reported (Chambers et al., 2009).

Conclusion

The growing trend in applying carbohydrate mouth rinsing with the aim to improve endurance exercise performance has grown over recent years. This is based on numerous scientific reports that have reported that the practice of rinsing a carbohydrate solution activates brain regions related to the sensation of reward and pleasure, which in turn improves the drive to exercise. Carbohydrate mouth rinsing is also proposed as an alternative to fluid ingestion as it potentially reduce the risk of gastrointestinal problems during exercise. Therefore, the application of carbohydrate mouth rinsing continues to gain popularity among recreational and well-trained athletes.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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