The effects of swilling an l(−)-menthol solution during exercise in the heat

The Effect of Menthol Mouth Rinsing and Fluid Temperature on Male Cycling Performance in Thermoneutral Conditions

PURPOSE

The purpose of this study was to determine the effect of a menthol (MEN) mouth rinse (MR) on cycling time trial (TT) performance in thermoneutral conditions and to explore the impact of fluid temperature (cold water [CW] or thermoneutral water [TNW]) on MEN's effect on performance.

METHODS

Twelve trained male cyclists (VO2 peak, 61.4 ± 12.1 mL/kg/min) completed a cycling TT in thermoneutral conditions (21 ± 0.2 °C, 40 ± 0.6% relative humidity) with four different mouth rinses: (1) MEN + CW; (2) MEN + TNW; (3) CW; and (4) TNW. The time to complete the TT and the power output (W) were recorded. The ratings of perceived exertion (RPE, Borg 6-20), thermal sensation (TS), and thermal comfort (TC) were recorded prior to and throughout the TT. The core body temperature (Tc) and heart rate (HR) were recorded throughout.

RESULTS

The TT duration was not significantly different between trials (MEN + TNW: 38:11 ± 12:48, MEN + CW: 37:21 ± 13:00, CW: 38:12 ± 13:54, TNW: 36:06 ± 14:12 mins:secs, p < 0.05). The mean trial power output did not significantly differ between conditions (>0.05). The Tc, HR, RPE, TS, and TC were not significantly different between trials (p > 0.05).

CONCLUSION

The results suggest that a MEN MR with either CW or TNW does not significantly improve cycling TT performance in trained male cyclists compared to a CW or TNW MR in thermoneutral conditions.

How Cool is That? The Effects of Menthol Mouth Rinsing on Exercise Capacity and Performance: A Systematic Review and Meta-analysis

BACKGROUND

Menthol (MEN) mouth rinsing (MR) has gained considerable interest in the athletic population for exercise performance; however, the overall magnitude of effect is unknown.

OBJECTIVE

The aim of this systematic review and meta-analysis was to determine the efficacy of menthol MEN MR and the impact it has on exercise capacity and performance.

METHODS

Three databases were searched with articles screened according to the inclusion/exclusion criteria. Three-level meta-analyses were used to investigate the overall efficacy of MEN MR and the impact it has on exercise capacity and performance. Meta-regressions were then performed with 1) mean VO2peak, 2) MEN swilling duration; 3) the MEN concentration of MR solution, 4) the number of executed swills throughout a single experiment, 5) the use of flavoured sweetened, non-caloric, or non-flavoured neutral solutions as controls, 6) mean environmental temperature at the time of exercise tests, and 7) exercise type as fixed factors to evaluate their influence on the effects of MEN MR.

RESULTS

Ten MEN MR studies included sufficient information pertaining to MEN MR and exercise performance and capacity. MR with MEN resulted in no significant change in capacity and performance (SMD = 0.12; 95% CI - 0.08, 0.31; p = 0.23, n = 1, tau21 < 0.0001, tau22 =  < 0.0001, I2 = 0%). No significant influence was detected in meta-regressions for VO2peak, (estimate: 0.03; df = 8; 95% CI - 0.03, 0.09; p = 0.27), swilling duration (5 vs. 10 s: 0.00; df = 16; 95% CI - 0.41, 0.41; p = 1.0), MEN concentration (low [0.01%] vs. high [0.1%]: - 0.08; df = 15; 95% CI - 0.49, 0.32; p = 0.67), number of swills (estimate: 0.02; df = 13; 95% CI - 0.05, 0.09; p = 0.56), the use of flavoured sweetener or non-caloric as control (non-flavoured vs. flavoured: 0.12; df = 16; 95% CI - 0.30, 0.55; p = 0.55) or mean room temperature during exercise tests (estimate: 0.01; df = 16; 95% CI - 0.02, 0.04; p = 0.62).

CONCLUSION

MEN MR did not significantly improve overall exercise capacity and performance, though those involved in endurance exercise may see benefits.

Performance Benefits of Pre- and Per-cooling on Self-paced Versus Constant Workload Exercise: A Systematic Review and Meta-analysis

BACKGROUND AND OBJECTIVE

Exercise in hot environments impairs endurance performance. Cooling interventions can attenuate the impact of heat stress on performance, but the influence of an exercise protocol on the magnitude of performance benefit remains unknown. This meta-analytical review compared the effects of pre- and per-cooling interventions on performance during self-paced and constant workload exercise in the heat.

METHODS

The study protocol was preregistered at the Open Science Framework ( https://osf.io/wqjb3 ). A systematic literature search was performed in PubMed, Web of Science, and MEDLINE from inception to 9 June, 2023. We included studies that examined the effects of pre- or per-cooling on exercise performance in male individuals under heat stress (> 30 °C) during self-paced or constant workload exercise in cross-over design studies. Risk of bias was assessed using the Cochrane Risk of Bias Tool for randomized trials.

RESULTS

Fifty-nine studies (n = 563 athletes) were identified from 3300 records, of which 40 (n = 370 athletes) used a self-paced protocol and 19 (n = 193 athletes) used a constant workload protocol. Eighteen studies compared multiple cooling interventions and were included more than once (total n = 86 experiments and n = 832 paired measurements). Sixty-seven experiments used a pre-cooling intervention and 19 used a per-cooling intervention. Average ambient conditions were 34.0 °C [32.3-35.0 °C] and 50.0% [40.0-55.3%] relative humidity. Cooling interventions attenuated the performance decline in hot conditions and were more effective during a constant workload (effect size [ES] = 0.62, 95% confidence interval [CI] 0.44-0.81) compared with self-paced exercise (ES = 0.30, 95% CI 0.18-0.42, p = 0.004). A difference in performance outcomes between protocols was only observed with pre-cooling (ES = 0.74, 95% CI 0.50-0.98 vs ES = 0.29, 95% CI 0.17-0.42, p = 0.001), but not per-cooling (ES = 0.45, 95% CI 0.16-0.74 vs ES = 0.35, 95% CI 0.01-0.70, p = 0.68).

CONCLUSIONS

Cooling interventions attenuated the decline in performance during exercise in the heat, but the magnitude of the effect is dependent on exercise protocol (self-paced vs constant workload) and cooling type (pre- vs per-cooling). Pre-cooling appears to be more effective in attenuating the decline in exercise performance during a constant workload compared with self-paced exercise protocols, whereas no differences were found in the effectiveness of per-cooling.

Central effects of mouth rinses on endurance and strength performance

Rinsing the mouth with a carbohydrate (CHO) solution has been shown to enhance exercise performance while reducing neuromuscular fatigue. This effect is thought to be mediated through the stimulation of oral receptors, which activate brain areas associated with reward, motivation, and motor control. Consequently, corticomotor responsiveness is increased, leading to sustained levels of neuromuscular activity prior to fatigue. In the context of endurance performance, the evidence regarding the central involvement of mouth rinse (MR) in performance improvement is not conclusive. Peripheral mechanisms should not be disregarded, particularly considering factors such as low exercise volume, the participant's fasting state, and the frequency of rinsing. These factors may influence central activations. On the other hand, for strength-related activities, changes in motor evoked potential (MEP) and electromyography (EMG) have been observed, indicating increased corticospinal responsiveness and neuromuscular drive during isometric and isokinetic contractions in both fresh and fatigued muscles. However, it is important to note that in many studies, MEP data were not normalised, making it difficult to exclude peripheral contributions. Voluntary activation (VA), another central measure, often exhibits a lack of changes, mainly due to its high variability, particularly in fatigued muscles. Based on the evidence, MR can attenuate neuromuscular fatigue and improve endurance and strength performance via similar underlying mechanisms. However, the evidence supporting central contribution is weak due to the lack of neurophysiological measures, inaccurate data treatment (normalisation), limited generalisation between exercise modes, methodological biases (ignoring peripheral contribution), and high measurement variability.Trial registration: PROSPERO ID: CRD42021261714.

The effect of menthol rinsing before intermittent exercise on physiological, physical, and thermo-behavioral responses of male football referees in hot and humid environment

Introduction

In the current experiment, we aimed to evaluate whether eliciting pre-exercise non-thermal cooling sensations would alter perceptual measures, and physical and physiological responses in football referees.

Methods

Nine highly trained male football referees undertook two 45-minute intermittent exercise protocols in hot and humid conditions (34.2 ± 0.6°C, 62.5 ± 1.0% relative humidity). In a randomized counterbalanced crossover design, 1 of 2 beverages were given before the warm-up: a 0.01% menthol solution or a placebo noncaloric solution. Physical performance was quantified as total distance covered in each of the three 15-minute exercise blocks. Core temperature, heart rate, thermal sensation and thermal comfort were measured at rest and after each exercise block.

Results

No changes were observed between trials and over time for distance covered. No main effect of mouth rinse was observed for core temperature and heart rate, but both increased over time in all conditions (P < 0.001). Thermal sensation and thermal comfort were significantly improved with menthol after mouth-rinsing (P < 0.05), but with no differences at any other time-point.

Discussion

These results indicate that non-thermal cooling oral stimuli provide immediate behavioral changes but may not influence physiological or physical responses in football referees, during intermittent exercise in hot and humid environments.

Clinical Trial Registration

www.clinicaltrials.gov, identifier NCT05632692.

Ad libitum ice slurry ingestion and half-marathon performance in a hot environment: A study comparing the effects of the amount and moment of ingestion between ice slurry and water at 37 °C

Ice slurry ingestion during prolonged exercises may improve performance in hot environments; however, the ideal amount and timing of ingestion are still uncertain. We determined whether ad libitum ice slurry ingestion influences physiological and perceptual variables and half-marathon performance while comparing the effects of the amount and moment of ingestion between ice slurry and water at 37 °C. Ten trained participants (28 ± 2 years; mean and SD) were required to run two half marathons while consuming either ice slurry (-1 °C; Ad-1) or water (37 °C; 37 CE) ad libitum. They then performed two other half marathons where, during one, they were required to ingest an amount of water equivalent to the amount consumed during the Ad-1 trial (Pro37), and in the other, to ingest ice slurry in the amount consumed during the 37 CE trial (Pro-1). During the half marathons, dry-bulb temperature and relative humidity were controlled at 33.1 ± 0.3 °C and 60 ± 3%, respectively. Ad-1 ingestion (349.6 ± 58.5 g) was 45% less than 37 CE ingestion (635.5 ± 135.8 g). Physical performance, heart rate, perceived exertion, body temperatures, and thermal perception were not influenced by the temperature or amount of beverage ingestion. However, a secondary analysis suggested that lower beverage ingestion was associated with improved performance (Ad-1 + Pro37 vs. 37 CE + Pro-1: -4.0 min, Cohen's d = 0.39), with a significant relationship between lower beverage ingestion and faster running time (b = 0.02, t = 4.01, p < 0.001). In conclusion, ice slurry ingestion does not affect performance or physiological or perceptual variables during a half marathon in a hot environment. Preliminary evidence suggests that lower beverage ingestion (ice slurry or warm water) is associated with improved performance compared to higher ingestion.

Food for thought: Physiological considerations for nutritional ergogenic efficacy

Top-class athletes have optimized their athletic performance largely through adequate training, nutrition, recovery, and sleep. A key component of sports nutrition is the utilization of nutritional ergogenic aids, which may provide a small but significant increase in athletic performance. Over the last decade, there has been an exponential increase in the consumption of nutritional ergogenic aids, where over 80% of young athletes report using at least one nutritional ergogenic aid for training and/or competition. Accordingly, due to their extensive use, there is a growing need for strong scientific investigations validating or invalidating the efficacy of novel nutritional ergogenic aids. Notably, an overview of the physiological considerations that play key roles in determining ergogenic efficacy is currently lacking. Therefore, in this brief review, we discuss important physiological considerations that contribute to ergogenic efficacy for nutritional ergogenic aids that are orally ingested including (1) the impact of first pass metabolism, (2) rises in systemic concentrations, and (3) interactions with the target tissue. In addition, we explore mouth rinsing as an alternate route of ergogenic efficacy that bypasses the physiological hurdles of first pass metabolism via direct stimulation of the central nervous system. Moreover, we provide real-world examples and discuss several practical factors that can alter the efficacy of nutritional ergogenic aids including human variability, dosing protocols, training status, sex differences, and the placebo effect. Taking these physiological considerations into account will strengthen the quality and impact of the literature regarding the efficacy of potential ergogenic aids for top-class athletes.

Peppermint essential oil (Mentha piperita L.) increases time to exhaustion in runners

PURPOSE

This study aimed to evaluate the capacity of peppermint essential oil to improve the physical performance of runners in running protocol until exhaustion.

METHODS

In a clinical, randomized, double-blind, cross-over and controlled study, fourteen male recreational runners (37.1 ± 2.0 years; 24 ± 1.1 kg/m2; 53.1 ± 1.7 mL kg min) performed two runs to exhaustion at 70% of VO2max, after intake of 500 mL of water added with 0.05 mL of peppermint essential oil (PEO) or placebo (PLA), plus 400 mL of the drink during the initial part of the exercise. Records were made of body temperature (BT), thermal sensation (TS), thermal comfort (TC), subjective perception of effort (SPE), sweat rate (SR), and urine volume and density.

RESULTS

Time to exhaustion was 109.9 ± 6.9 min in PEO and 98.5 ± 6.2 min in PLA (p = 0.009; effect size: 0.826). No significant changes were observed in the values of BT, TS, TC, SPE, SR, lost body mass, and urine volume and density (p > 0.05).

CONCLUSION

Peppermint essential oil added to water before and during a race significantly increases the time to exhaustion of recreational runners but without altering BT, TS, TC, or hydration status, so the mechanisms involved were not clarified in this study.

BRAZILIAN REGISTRY OF CLINICAL TRIALS (REBEC)

RBR-75zt25z.

Cumulative pre-cooling methods do not enhance cycling performance in tropical climate

The main objective of this study was to investigate the effect of mixed cooling techniques (combination of internal and external strategies, with and without menthol) during warm-up for a time trial in tropical climate. Seven heat-acclimatized trained male road cyclists participated in three experimental sessions consisting of 20-min cycling performances on a velodrome track in ecological hot and humid conditions (Guadeloupe, French West Indies; WBGT: 27.64±0.27°C; relative humidity: 76.43±2.19%), preceded by a standardized 30-min warm-up and the ingestion of cold menthol water (1) with a cooling vest soaked in ice water (ICE-VEST), (2) with a cooling vest soaked in ice menthol water (MEN-VEST), and (3) without a vest (NO-VEST). Cycling performance (total distance, distance traveled per 2-min block), physiological parameters (core body temperature recorded, heart rate) and perceptions (exertion, thermal comfort, thermal sensation) were assessed. No between-condition differences were found for physiological parameters, the total covered distance or the distance traveled per 2-min block. However, distance traveled per 2-min decreased with time (p = 0.03), with no difference between conditions, suggesting a variation in pace during the cycling performance trial (e.g., mean±SD: 1321±48.01m at T2; 1308±46.20m at T8, 1284±78.38m at T14, 1309±76.29m at T20). No between-condition differences were found for perception of exertion, thermal comfort and thermal sensation during the warm-up (11.83±3.34; 2.58±1.02; 4.39±0.94, respectively) and the performance (17.85±0.99; 2.70±1.25; 5.20±1.20, respectively) but the pairwise comparisons within condition revealed a significant increase of TS values from T0 (4.57±1.13) to T20 (6.00±0.58) only in NO-VEST condition (p = 0.04). The absence of modification of thermal sensation at the end of the cycling test under the mixed conditions (ICE-VEST and MEN-VEST) suggests a beneficial effect of wearing a cooling vest on thermal sensation although it had no effect on performance.

Topical application of isolated menthol and combined menthol-capsaicin creams: Exercise tolerance, thermal perception, pain, attentional focus and thermoregulation in the heat

We determined the effects of topically applied (i) isolated menthol cream, (ii) menthol and capsaicin co-application or (iii) placebo cream on exercise tolerance, thermal perception, pain, attentional focus and thermoregulation during exercise in the heat. Ten participants cycled at 70% maximal power output until exhaustion in 35°C and 20% relative humidity after application of (i) 5% isolated menthol, (ii) 5% menthol and 0.025% capsaicin co-application or (iii) placebo cream. Thermo-physiological responses were measured during exercise, with attentional focus and pain determined post-exercise on a 0-to-10 scale. Across the three conditions, time to exhaustion was 13.4 ± 4.8 min, mean ± SD infrared tympanic and skin temperature was 37.2 ± 0.6°C and 35.1 ± 1.2°C, respectively, and heart rate was 152 ± 47 bpm, with no changes between conditions (p > 0.05). Perceived exertion was lower in the isolated menthol vs. all other conditions (p < 0.05, ηp2 = 0.44). Thermal sensation was higher in menthol-capsaicin co-application vs. isolated menthol (p < 0.05, d = 1.1), while sweat rate was higher for capsaicin and menthol co-application compared to menthol (p < 0.05, d = 0.85). The median and interquartile range scores for pain were lower (p < 0.05) in the menthol condition (8, 7-8) compared to both menthol and capsaicin (10, 9-10) and placebo (9, 9-10), which was coupled with a greater distraction (p < 0.05) in the menthol condition (9, 7-10) compared to placebo (6, 5-7). Despite no performance effects for any topical cream application condition, these data reiterate the advantageous perceptual and analgesic role of menthol application and demonstrate no advantage of co-application with capsaicin.HighlightsTopical application of isolated menthol cream to cold-sensitive areas of the body during exhaustive exercise in the heat, elicited reduced perception of pain and enhanced sensation of cooling.While this reduction in generally unpleasant feelings (i.e. pain and heat) were coupled with lower RPE scores in the menthol condition and could be considered beneficial, there was no apparent ergogenic effect in an exercise tolerance test.Co-application of capsaicin and menthol appeared to inhibit the positive sensory effects elicited by menthol.Isolated menthol can induce changes in cognitive processes related to pain and exertion, while also reducing thermal sensation; however, the decision to use menthol creams must be balanced with the limited performance or thermoregulatory effects reported herein during exercise in hot environments.

Menthol mouth rinsing and performance in elite football referees in the heat: A study protocol for a randomized crossover trial

Background

Within professional European competitions, matches can be played in extreme environmental temperatures, ranging from -5 °C to +30 °C in different countries. Furthermore, the World Cups are usually played in the summer months, when temperatures can exceed 35 °C, increasing physiological stress. Practical and cost-effective cooling strategies may be implemented to help players and referees to cope with exercising in the heat. No study has evaluated the effect of non-thermal internal cooling techniques regarding performance responses on elite football referees, so far. This study aims to analyse the effects of a menthol mouth rinse regarding physical, physiological, and perceptual performance in elite male football referees, during a 90-min football protocol in the heat.

Methods

At least thirteen male football referees will be recruited to perform two intermittent football protocols, separated by no less than 7 days. After passing the eligibility criteria, the participants will be randomly assigned to 1 of 2 beverages: (1) intervention - menthol solution 0.01% and (2) placebo - noncaloric berry-flavored solution, both at room temperature. The beverages will be given before warm-up (pre-cooling) and at the half-time (per-cooling). The trials will follow a randomized counterbalanced crossover design, single blinded, and will take place in indoor facilities, with Wet Bulb Globe Temperature (WBGT) > 30 °C, at the same time of the day to control for circadian variations.

Impact of the project

The results of this study are expected to determine whether mouth rinsing a menthol solution before and during a football exercise protocol performed in the heat will alter perceptual measures and help ease physiological strain and attenuate performance decrements in elite male football referees, comparing to a non-cooling strategy. Thus, we can be closer to defining nutritional strategies of internal cooling that may be an advantage for the performance of the football referees in the heat.

Trial registration

www.ClinicalTrials.gov NCT05632692 registered on 20 November 2022.

A 0.1% L-Menthol Mouth Swill in Elite Male Rugby Players Has Different Effects in Forwards and Backs

PURPOSE

Menthol mouth swills can improve endurance performance in the heat, which is attributed to attenuations in nonthermally derived thermal sensation (TS) and perception of effort. However, research in elite team-sport athletes is absent. Therefore, this study investigated the performance and TS responses to a 0.1% menthol mouth rinse (MR) or placebo (PLA) among elite male rugby union players.

METHOD

Twenty-seven (15 Forwards and 12 Backs) elite male Super Rugby players completed two 3-minute 15-a-side rugby-specific conditioning blocks, with MR or PLA provided at the start of training (baseline), at the start of each 3-minute block (swill 1 [S1] and swill 2 [S2]), and at the end of training (swill 3 [S3]). TS was assessed using the American Society of Heating, Refrigerating and Air-Conditioning Engineers 9-point Analog Sensation Scale after each swill and at baseline (preconditioning block). Acceptability was measured after baseline swill and S3 using a 5-question Likert scale. Physical performance was measured throughout training using global positioning system metrics.

RESULTS

MR attenuated TS from baseline to S1 (P = .003, SD = 1.01) and S2 (P = .002, SD = 1.09) in Forwards only, compared with PLA. Acceptability was higher only for Forwards in MR versus PLA at baseline (P = .003, SD = 1.3) and S3 (P = .004, SD = 0.75). MR had no effect on physical performance metrics (P > .05).

CONCLUSION

MR attenuated the rise in TS with higher acceptability at S1 and S3 (in Forwards only) with no effect on selected physical performance metrics. Longer-duration exercise (eg, a match) in hot-humid conditions eliciting markedly increased body temperatures could theoretically allow favorable changes in TS to enhance performance-these postulations warrant experimental investigation.

L-menthol administration facilitates breathing comfort during exhaustive endurance running and improves running capacity in well-trained runners: A randomized crossover study

ABSTRACTThis study aimed to clarify the contribution of L-menthol administration to endurande exercise capacity. Thirteen male runners (age, 35.8 ± 7.8 years; peak oxygen uptake, 62.7 ± 6.8 mL kg-1 min-1) ran on treadmills at fixed intensities of their anaerobic thresholds to exhaustion. All participants underwent three trials-water ingestion (W-IG), L-menthol mouth rinsing (M-MR), and L-menthol ingestion (M-IG)- in a random order every 5 min while running. Breathing comfort (BC) was measured immediately after fluid intake. Dyspnea threshold against external inspiratory resistance was examined before and after the running test. The running time with M-IG (1683.9 ± 520.3 s) was longer than that with W-IG (1410.2 ± 465.9 s, effect size [ES] = 0.55). BC with M-IG (2.00 ± 0.74) was higher than that with W-IG (0.42 ± 0.79) at exhaustion (ES > 2.00). The dyspnea threshold after running decreased to 19.2 ± 7.6 cm H₂O L-1 s-1 with W-IG, whereas that with M-MR (26.2 ± 6.5 cm H₂O L-1 s-1) and M-IG (29.2 ± 2.8 cm H₂O L-1 s-1) remained high (p for interaction < 0.001). M-IG facilitated BC during running, improved endurance capacity, and prevented decreases in the dyspnea threshold against external inspiratory resistance after exhaustive running.HighlightsL-menthol ingestion facilitated breathing comfort during high intensity endurance running and improved exhaustive endurance running capacity.Even after exhaustion, L-menthol solution relieved dyspnea sensitivity against external inspiratory resistance.L-menthol ingestion might help athletes improve their endurance running capacity.

Distinguishing science from pseudoscience in commercial respiratory interventions: an evidence-based guide for health and exercise professionals

Respiratory function has become a global health priority. Not only is chronic respiratory disease a leading cause of worldwide morbidity and mortality, but the COVID-19 pandemic has heightened attention on respiratory health and the means of enhancing it. Subsequently, and inevitably, the respiratory system has become a target of the multi-trillion-dollar health and wellness industry. Numerous commercial, respiratory-related interventions are now coupled to therapeutic and/or ergogenic claims that vary in their plausibility: from the reasonable to the absurd. Moreover, legitimate and illegitimate claims are often conflated in a wellness space that lacks regulation. The abundance of interventions, the range of potential therapeutic targets in the respiratory system, and the wealth of research that varies in quality, all confound the ability for health and exercise professionals to make informed risk-to-benefit assessments with their patients and clients. This review focuses on numerous commercial interventions that purport to improve respiratory health, including nasal dilators, nasal breathing, and systematized breathing interventions (such as pursed-lips breathing), respiratory muscle training, canned oxygen, nutritional supplements, and inhaled L-menthol. For each intervention we describe the premise, examine the plausibility, and systematically contrast commercial claims against the published literature. The overarching aim is to assist health and exercise professionals to distinguish science from pseudoscience and make pragmatic and safe risk-to-benefit decisions.

A Menthol-Enhanced "Cooling" Energy Gel Does Not Influence Laboratory Time Trial Performance in Trained Runners

l-menthol (menthol) is an organic compound derived from peppermint which imparts a refreshing mint flavor and aroma to oral hygiene products, chewing gum, and topical analgesics. Menthol has been identified as a non-thermal sensory cooling strategy for athletes when ingested or mouth-rinsed during exercise in hot environments. Therefore, sports nutrition products delivering a controlled concentration of menthol could be beneficial for athletes exercising in the heat. We sought to test the performance and perceptual outcomes of a novel menthol energy gel during treadmill running in the heat (33 °C, 49% RH). Fourteen trained runners (mean ± SD; age: 31 ± 6 years, VO2max: 56.5 ± 10.1 mL·kg-1·min-1, BMI: 23.2 ± 2.4 kg/m2; six female) participated in a randomized, crossover, double-blind, and placebo-controlled study. A menthol-enhanced energy gel (0.5% concentration; MEN) or flavor-matched placebo (PLA) was ingested 5 min before and again at 20 and 40 min of a 40 min treadmill exercise preload at 60% VO2max, followed by a 20 min self-paced time trial. The total distance, vertical distance, perceptual measures (thermal comfort, thermal sensation, rating of perceived exertion, and affect), and cognitive performance via computerized neurocognitive assessment were measured. No difference between 20 min self-paced time trial total distance (MEN: 4.22 ± 0.54 km, PLA: 4.22 ± 0.55 km, p = 0.867), vertical distance (MEN: 49.2 ± 24.6 m, PLA: 44.4 ± 11.4 m, p = 0.516), or any perceptual measures was observed (all p > 0.05). Cognitive performance was not different between the trials (all p > 0.05). These results suggest that a menthol energy gel is not superior to a non-menthol gel in terms of performance or perception during treadmill running in the heat. More research is needed to confirm whether these findings translate to ecologically valid settings, including outdoor exercise in ambient heat and during competition.

Carbohydrate mouth rinse is no more effective than placebo on running endurance of dehydrated and heat acclimated athletes

PURPOSE

To determine whether carbohydrate mouth rinsing would improve endurance running performance of tropical natives in a warm-humid (30 °C and 70% relative humidity) environment.

METHOD

Twelve endurance male runners [age 25 ± 3 years; peak aerobic capacity ([Formula: see text]O_2peak) 57.6 ± 3.6 mL^.kg^-1.min^-1] completed three time-to-exhaustion (TTE) trials at ~ 70% [Formula: see text]O_2peak while swilling 25 ml of a 6% carbohydrate (CHO) or taste-matched placebo (PLA) as well as no mouth rinse performed in the control (CON) trial.

RESULTS

TTE performance was significantly longer in both CHO and PLA trials when compared with the CON trial (54.7 ± 5.4 and 53.6 ± 5.1 vs. 48.4 ± 3.6 min, respectively; p < 0.001 and p = 0.012, respectively), but was not significantly different between CHO and PLA trials (p = 1.000). The rating of perceived exertion was not different between the CHO and PLA trials, however, was significantly affected when compared to the CON trial (p < 0.001). A similar effect was observed for perceived arousal level between the CHO and PLA trials to the CON trial. Core temperature, mean skin temperature and skin blood flow were not significantly different between the three trials (all p > 0.05). Similarly, plasma lactate and glucose as well as exercise heart rate were not influenced by the trials.

CONCLUSIONS

The present study demonstrates that mouth rinsing, whether carbohydrate or placebo, provides an ergogenic benefit to running endurance when compared to CON in a heat stress environment. Nevertheless, the results do not support the notion that rinsing a carbohydrate solution provides a greater advantage as previously described among non-heat acclimated individuals within a temperate condition.

Performance effects of internal pre- and per-cooling across different exercise and environmental conditions: A systematic review

Exercise in a hot and humid environment may endanger athlete's health and affect physical performance. This systematic review aimed to examine whether internal administration of ice, cold beverages or menthol solutions may be beneficial for physical performance when exercising in different environmental conditions and sports backgrounds. A systematic search was performed in PubMed, Web of Science, Scopus and SPORTDiscus databases, from inception to April 2022, to identify studies meeting the following inclusion criteria: healthy male and female physically active individuals or athletes (aged ≥18 years); an intervention consisting in the internal administration (i.e., ingestion or mouth rinse) of ice slush, ice slurry or crushed ice and/or cold beverages and/or menthol solutions before and/or during exercise; a randomized crossover design with a control or placebo condition; the report of at least one physical performance outcome; and to be written in English. Our search retrieved 2,714 articles in total; after selection, 43 studies were considered, including 472 participants, 408 men and 64 women, aged 18-42 years, with a VO2max ranging from 46.2 to 67.2 mL⋅kg-1⋅min-1. Average ambient temperature and relative humidity during the exercise tasks were 32.4 ± 3.5°C (ranging from 22°C to 38°C) and 50.8 ± 13.4% (varying from 20.0% to 80.0%), respectively. Across the 43 studies, 7 exclusively included a menthol solution mouth rinse, 30 exclusively involved ice slurry/ice slush/crushed ice/cold beverages intake, and 6 examined both the effect of thermal and non-thermal internal techniques in the same protocol. Rinsing a menthol solution (0.01%) improved physical performance during continuous endurance exercise in the heat. Conversely, the ingestion of ice or cold beverages did not seem to consistently increase performance, being more likely to improve performance in continuous endurance trials, especially when consumed during exercises. Co-administration of menthol with or within ice beverages seems to exert a synergistic effect by improving physical performance. Even in environmental conditions that are not extreme, internal cooling strategies may have an ergogenic effect. Further studies exploring both intermittent and outdoor exercise protocols, involving elite male and female athletes and performed under not extreme environmental conditions are warranted. Systematic review registration: [https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021268197], identifier [CRD42021268197].

Ice slurry ingestion improves physical performance during high-intensity intermittent exercise in a hot environment

Ice slurry ingestion enhances exercise performance by lowering the core body temperature. However, an operational issue related to this ingestion is the requirement for a high intake of 7.5 g·kg^-1 to produce the desired effects. We investigated the effects of the intake of low amounts of ice slurry at −2°C on the tympanic temperature and exercise performance during repeated high-intensity intermittent exercises in a hot environment. This study was a randomized, crossover study, with a 6-day washout period. Twelve university rugby union players performed two 30-min sessions of high-intensity intermittent exercises separated by a 15-min half-time break on a cycle ergometer in a hot environment (28.8°C ± 0.1°C, 49.5% ± 0.6% relative humidity). The participants ingested 450 g of −2°C-ice slurry (ICE), or a 30°C-beverage (CON) having the same composition as ICE, or 30°C-water (WAT) during the half-time break. The tympanic temperature and skin temperature were measured as the physiological data, and the peak power and mean power as the exercise performance data. The tympanic temperature at the half-time break and beginning of the 2^nd session was significantly lower in the ICE group as compared with the CON and WAT groups. The skin temperature at the half-time break was significantly lower in the ICE group as compared with the WAT group. While the peak power and mean power during the 2^nd session were significantly greater in the ICE group as compared with the CON and WAT groups. Our findings suggest that even the intake of lower amounts, as compared with those used in previous studies, of low-temperature ice slurry can reduce the body temperature and improve the peak power. These results suggest that intake of low-temperature ice slurry as a strategy for internal body cooling is useful for improving endurance exercise performance in hot environments.

Effects of hot and humid environments on thermoregulation and aerobic endurance capacity of Laser sailors

Objectives

The purpose was to investigate the effects of hot and humid environments on thermoregulation and aerobic endurance capacity and whether high skin temperature serves as a more important thermoregulatory factor affecting aerobic exercise capacity.

Methods

A randomized cross-over design was applied to this study, in which nine Laser sailors performed the 6 km rowing test (6 km test) in both a warm (ambient temperature: 23 ± 1.4 °C; relative humidity: 60.5 ± 0.7%; wind speed: 0 km/h; WARM) and hot environment (ambient temperature: 31.8 ± 1.1 °C; relative humidity: 63.5 ± 4.9%; wind speed: 3.5 ± 0.7 km/h; HOT).

Results

The time for completing 6 km test of HOT group was significantly longer than that of WARM group (P = 0.0014). Mean power of 3–4 km, 4–5 km and 5–6 km were significant lower in HOT group (P = 0.014, P = 0.02, P = 0.003). Gastrointestinal temperature and skin temperature were significantly higher in HOT group during the 6 km test (P = 0.016, P = 0.04). Heat storage at 5 min and 15 min of HOT group were significantly higher than that of WARM group (P = 0.0036; P = 0.0018). Heart rate and physiological strain index of HOT group were significantly higher than that of WARM group during the 6 km test (P = 0.01, P < 0.01).

Conclusion

When skin temperature and core temperature both increased, high skin temperature may be the more important thermoregulatory factor that affected the aerobic endurance performance in hot and humid environments. The high skin temperature narrowed the core to skin temperature gradient and skin to ambient temperature gradient, which may result in greater accumulation of heat storage. The greater heat storage led to the lower muscle power output, which contributed to the reduction of the heat production.

The Influence of L-menthol on Time Trial Running Performance in Recreational Runners

Purpose: This study investigated the effects of combined mouth rinse and topical application of L-menthol on perceptual responses and running performance under thermoneutral conditions (22 ± 2°C and 30-60% relative humidity). Methods: Twelve recreational male runners (age: 31.7 ± 3.8 years; age range: 27-39 years) completed a familiarization, a control test (CON) and two maximal 10-km time trials (counterbalanced randomized crossover design) performed in different days with a non-thermal cooling intervention (combined application of a L-menthol mouth rinse and topical L-menthol gel - MEN) or placebo (PLA). Performance and perceptual measures (thermal sensation, thermal comfort, ratings of perceived exertion and affective response) were recorded for every km completed in the 10-km test. Results: Performance time was lower in MEN (P = 0.03) and PLA (P = 0.003) compared to CON, but no differences were found between MEN vs PLA (P = 1.00). All perceptual responses increased over time in all conditions (P < 0.0001), but only the thermal sensation was lower (P = 0.01) in the MEN compared to CON. Conclusion: L-menthol strategies promote fresh sensations and may improve running performance in 10-km time trial in recreational runners, but the performance improvement could mainly be due to a placebo effect.

Menthol Mouth Rinsing Maintains Relative Power Production during Three-Minute Maximal Cycling Performance in the Heat Compared to Cold Water and Placebo Rinsing

Previous menthol studies have demonstrated ergogenic effects in endurance-based activity. However, there is a need for research in sports whose physiological requirements exceed maximal aerobic capacity. This study assessed the effects of 0.1% menthol mouth-rinsing upon a modified three-minute maximal test in the heat (33.0 ± 3.0 °C; RH 46.0 ± 5.0%). In a randomised crossover single blind placebo-controlled study, 11 participants completed three modified maximal tests, where each trial included a different mouth rinse: either menthol (MEN), cold water (WAT) or placebo (PLA). Participants were asked to rate their thermal comfort (TC), thermal sensation (TS) and rating of perceived exertion (RPE) throughout the test. Heart rate, core temperature, oxygen uptake (VO₂), ventilation (VE) and respiratory exchange ratio (RER) were monitored continuously throughout the test, alongside cycling power variables (W; W/kg). A blood lactate (BLa) level was taken pre- and post- test. Small to moderate effects (Cohen's d and accompanying 90% confidence intervals) between solutions MEN, WAT and PLA were observed towards the end of the test in relation to relative power. Specifically, from 75-105 s between solutions MEN and WAT (ES: 0.795; 90% CI: 0.204 to 1.352) and MEN and PLA (ES: 1.059; 90% CI: 0.412 to 1.666), this continued between MEN and WAT (ES: 0.729; 90% CI: 0.152 to 1.276) and MEN and PLA (ES: 0.791; 90% CI: 0.202 to 1.348) from 105-135 s. Between 135-165 s there was a moderate difference between solutions MEN and WAT (ES: 1.058; 90% CI: 0.411 to 1.665). This indicates participants produced higher relative power for longer durations with the addition of the menthol mouth rinse, compared to cold water or placebo. The use of menthol (0.1%) as a mouth rinse showed small performance benefits for short duration high intensity exercise in the heat.

The Effect of Isolated and Combined Application of Menthol and Carbohydrate Mouth Rinses on 40 km Time Trial Performance, Physiological and Perceptual Measures in the Heat

The current study compared mouth swills containing carbohydrate (CHO), menthol (MEN) or a combination (BOTH) on 40 km cycling time trial (TT) performance in the heat (32 °C, 40% humidity, 1000 W radiant load) and investigates associated physiological (rectal temperature (Trec), heart rate (HR)) and subjective measures (thermal comfort (TC), thermal sensation (TS), thirst, oral cooling (OC) and RPE (legs and lungs)). Eight recreationally trained male cyclists (32 ± 9 y; height: 180.9 ± 7.0 cm; weight: 76.3 ± 10.4 kg) completed familiarisation and three experimental trials, swilling either MEN, CHO or BOTH at 10 km intervals (5, 15, 25, 35 km). The 40 km TT performance did not differ significantly between conditions (F2,14 = 0.343; p = 0.715; η2 = 0.047), yet post-hoc testing indicated small differences between MEN and CHO (d = 0.225) and MEN and BOTH (d = 0.275). Subjective measures (TC, TS, RPE) were significantly affected by distance but showed no significant differences between solutions. Within-subject analysis found significant interactions between solution and location upon OC intensity (F28,196 = 2.577; p < 0.001; η2 = 0.269). While solutions containing MEN resulted in a greater sensation of OC, solutions containing CHO experienced small improvements in TT performance. Stimulation of central CHO pathways during self-paced cycling TT in the heat may be of more importance to performance than perceptual cooling interventions. However, no detrimental effects are seen when interventions are combined.

Commercially available carbohydrate drink with menthol fails to improve thermal perception or cycling exercise capacity in males

The purpose of this double-blinded, crossover randomized and counterbalanced study was to compare the effects of ingesting a tepid commercially available carbohydrate-menthol-containing sports drink (menthol) and an isocaloric carbohydrate-containing sports drink (placebo) on thermal perception and cycling endurance capacity "in a simulated home virtual cycling environment". It was hypothesized that the addition of menthol would improve indicators of thermal perception and improve endurance exercise capacity. Twelve healthy, endurance-trained males (age 29 ± 5 years, height 181 ± 6 cm, body mass 79 ± 2 kg and V̇O₂max 57.3 ± 6.4 mL kg^-1 min^-1) completed two experimental trials on a stationary bicycle without external air flow. Each trial consisted of (1) cycling for 60 min at 90% of the first ventilatory threshold while receiving a fixed amount of menthol or placebo every 10 min followed immediately by (2) cycling until volitional exhaustion (TTE) at 105% of the intensity corresponding to the respiratory compensation point. TTE did not differ between both conditions (541 ± 177 and 566 ± 150 s for menthol and placebo; p > 0.05) and neither did ratings of perceived thermal comfort or thermal sensation (p > 0.05). Also, the rectal temperature at the end of TTE was comparable between menthol and placebo trials (38.7 ± 0.2°C and 38.7 ± 0.3°C, respectively; p > 0.05). The present results demonstrate that the addition of menthol to commercially available sports drink does not improve thermal comfort or endurance exercise capacity during ∼65 min of intense virtual cycling.

Dilution Method of Menthol Solutions Affects Subsequent Perceptual Thermal Responses during Passive Heat Exposure in Non-Heat Acclimated Participants

Due to its volatility, the qualitative experience of menthol may be modulated by its preparation and combination with other compounds. One such method of preparation is dilution, with two dilution methods existing within the sport and exercise science literature, where menthol is used to impart feelings of oral cooling and improve thermal comfort and sensation during heat exposure. This study compared these two dilution methods; one using a solvent the other using temperature, via a randomized counterbalanced repeated measures design (n = 12; Height: 174.0 ± 8.5 cm Mass: 73.4 ± 13.3 kg Age: 28.7 ± 8.4 y; two exposures to each solution) to assess the effect of solution and heat exposure, upon thermal comfort, thermal sensation and associated physiological parameters in non-heat acclimated participants. Thermal comfort was significantly affected by solution (p = 0.041; η2 = 0.017) and time (p < 0.001; η2 = 0.228), whereas thermal sensation was significantly affected by time only (p = 0.012; η2 = 0.133), as was tympanic temperature (p < 0.001; η2 = 0.277). Small to moderate clear differences between solutions at matched time points were also observed. These trends and effects suggest that, depending upon the dilution method employed, the resultant perceptual effects are likely impacted; this also likely depends upon the timing of menthol administration within a heat exposure session.

Temperate Air Breathing Increases Cycling Performance in Hot and Humid Climate Environment

Practicing physical activity in a hot and humid climate (HHC) is becoming increasingly common due to anthropogenic climate change and the growing number of international sports events held in warm countries. The aim of this study was to understand the physiological and psychological effects of breathing two air temperatures during cycling exercise in HHC. Ten male athletes performed two sessions of exercise in HHC (T°: 32.0 ± 0.5 °C, relative humidity: 78.6 ± 0.7%) during which they breathed hot air (HA, 33.2 ± 0.06 °C) or temperate air (TA, 22.6 ± 0.1 °C). Each session was composed of 30 min of pre-fatigue cycling at constant intensity, followed by a 10 min self-regulated performance. During pre-fatigue, TA induced a better feeling score and a lower rating of perceived effort (respectively, +0.9 ± 0.2, p < 0.05; 1.13 ± 0.21; p < 0.05) with no changes in physiological parameters. During performance, oxygen consumption and mechanical workload were increased by TA (respectively, +0.23 ± 0.1 L min⁻¹, p < 0.05 and +19.2 ± 6.1 W, p < 0.01), whereas no significant differences were observed for psychological parameters. Reducing the breathed air temperature decreased the discomfort induced by HHC during exercise and increased the performance capacity during self-regulated exercise. Thus, breathed air temperature perception is linked to the hardship of training sessions and directly contributes to the performance decrease in HHC.

Sports Dietitians Australia Position Statement: Nutrition for Exercise in Hot Environments

It is the position of Sports Dietitians Australia (SDA) that exercise in hot and/or humid environments, or with significant clothing and/or equipment that prevents body heat loss (i.e., exertional heat stress), provides significant challenges to an athlete's nutritional status, health, and performance. Exertional heat stress, especially when prolonged, can perturb thermoregulatory, cardiovascular, and gastrointestinal systems. Heat acclimation or acclimatization provides beneficial adaptations and should be undertaken where possible. Athletes should aim to begin exercise euhydrated. Furthermore, preexercise hyperhydration may be desirable in some scenarios and can be achieved through acute sodium or glycerol loading protocols. The assessment of fluid balance during exercise, together with gastrointestinal tolerance to fluid intake, and the appropriateness of thirst responses provide valuable information to inform fluid replacement strategies that should be integrated with event fuel requirements. Such strategies should also consider fluid availability and opportunities to drink, to prevent significant under- or overconsumption during exercise. Postexercise beverage choices can be influenced by the required timeframe for return to euhydration and co-ingestion of meals and snacks. Ingested beverage temperature can influence core temperature, with cold/icy beverages of potential use before and during exertional heat stress, while use of menthol can alter thermal sensation. Practical challenges in supporting athletes in teams and traveling for competition require careful planning. Finally, specific athletic population groups have unique nutritional needs in the context of exertional heat stress (i.e., youth, endurance/ultra-endurance athletes, and para-sport athletes), and specific adjustments to nutrition strategies should be made for these population groups.

Menthol Mouth Rinsing Is More Than Just a Mouth Wash-Swilling of Menthol to Improve Physiological Performance

Interventions that solely act on the central nervous system (CNS) are gaining considerable interest, particularly products consumed through the oral cavity. The oropharyngeal cavity contains a wide array of receptors that respond to sweet, bitter, and cold tastants, all of which have been shown to improve physiological performance. Of late, the ergogenic benefits of carbohydrate (CHO) and caffeine (CAF) mouth rinsings (MRs) have been widely studied; however, less is known about menthol (MEN). That the physiological state and environmental conditions impact the response each product has is increasingly recognized. While the effects of CHO and CAF MRs have been thoroughly studied in both hot and thermoneutral conditions, less is known about MEN as it has only been studied in hot environments. As such, this review summarizes the current knowledge regarding the MEN MR and exercise modality, frequency of the mouth rinse, and mouth rinse duration and compares two different types of study designs: time trials vs. time to exhaustion (TTE).

Exercise under heat stress: thermoregulation, hydration, performance implications, and mitigation strategies

A rise in body core temperature and loss of body water via sweating are natural consequences of prolonged exercise in the heat. This review provides a comprehensive and integrative overview of how the human body responds to exercise under heat stress and the countermeasures that can be adopted to enhance aerobic performance under such environmental conditions. The fundamental concepts and physiological processes associated with thermoregulation and fluid balance are initially described, followed by a summary of methods to determine thermal strain and hydration status. An outline is provided on how exercise-heat stress disrupts these homeostatic processes, leading to hyperthermia, hypohydration, sodium disturbances, and in some cases exertional heat illness. The impact of heat stress on human performance is also examined, including the underlying physiological mechanisms that mediate the impairment of exercise performance. Similarly, the influence of hydration status on performance in the heat and how systemic and peripheral hemodynamic adjustments contribute to fatigue development is elucidated. This review also discusses strategies to mitigate the effects of hyperthermia and hypohydration on exercise performance in the heat by examining the benefits of heat acclimation, cooling strategies, and hyperhydration. Finally, contemporary controversies are summarized and future research directions are provided.

Menthol Mouth Rinsing and Cycling Performance in Females Under Heat Stress

PURPOSE

The effects of menthol (MEN) mouth rinse (MR) on performance, physiological, and perceptual variables in female cyclists during a 30-km independent time trial (ITT) were tested.

METHODS

The participants (n = 9) cycled for 30 km in hot conditions (30°C [0.6°C], 70% [1%] relative humidity, 12 [1] km/h wind speed) on 2 test occasions: with a placebo MR and with MEN MR. Handgrip and a 5-second sprint were measured before, following the first MR, and after the ITT. Ratings of perceived exertion Borg 6 to 20, thermal sensation, and thermal pleasantness were recorded every 5 km. Core temperature and heart rate were recorded throughout.

RESULTS

The ITT performance significantly improved with MEN MR by 2.3% (2.7%) relative to the placebo (62.6 [5.7] vs 64.0 [4.9] min P = .034; d = 0.85; 95% confidence interval, 0.14 to 2.8 min). The average power output was significantly higher in the MEN trial (P = .031; d = 0.87; 95% confidence interval, 0.9 to 15.0 W). No significant interaction of time and MR for handgrip (P = .581, η2 = .04) or sprint was observed (P = .365, η2 = .103). Core temperature, heart rate, ratings of perceived exertion, and thermal sensation did not significantly differ between trials at set distances (P > .05). Pleasantness significantly differed between the placebo and MEN only at 5 km, with no differences at other TT distances.

CONCLUSION

These results suggest that a nonthermal cooling agent can improve 30-km ITT performance in female cyclists, although the improved performance with MEN MR is not due to altered thermal perception.

The elderly's physiological and perceptual responses to cooling during simulated activities of daily living in UK summer climatic conditions

OBJECTIVES

The elderly are the most at-risk population for heat-related illness and mortality during the periods of hot weather. However, evidence-based elderly-specific cooling strategies to prevent heat-illness are limited. The aim of this investigation was to quantify the elderly's physiological and perceptual responses to cooling through cold water ingestion (COLD) or an L-menthol mouth rinse (MENT) during simulated activities of daily living in UK summer climatic conditions.

STUDY DESIGN

Randomised, controlled repeated measures research design.

METHODS

A total of ten participants (men n = 7, women n = 3: age; 69 ± 3 yrs, height; 168 ± 10 cm, body mass; 68.88 ± 13.72 kg) completed one preliminary and three experimental trials; control (CON), COLD and MENT. Experimental trials consisted of 40 min rest followed by 30 min of cycling exercise at 6 metabolic equivalents and a 6-min walk test (6MWT), within a 35 °C, 50% relative humidity environment. Experimental interventions (every 10 min); cold water (4 °C) ingestion (total of 1.5L) or menthol (5 ml mouth swill for 5 s, menthol concentration of 0.01%).

RESULTS

Peak rectal temperature (T_re) was significantly (P < 0.05) lower in COLD compared with CON (-0.34 ± 0.16 °C) and MENT (-0.36 ± 0.20 °C). End exercise heart rate (HR) decreased in COLD compared with CON (-7 ± 9 b min^-1) and MENT (-6 ± 7 b min^-1). There was no difference in end exercise thermal sensation (TS) (CON; 6.1 ± 0.4, COLD; 6.0 ± 0.4, MENT; 6.4 ± 0.6) or thermal comfort (TC) (CON; 4 ± 1, COLD; 4 ± 1, MENT; 4 ± 1) between trials. The participants walked significantly further during the COLD 6MWT compared with CON (40 m ± 40 m) and MENT (40 m ± 30 m). There was reduced physiological strain in the COLD 6MWT compared with CON (T_re; -0.21 ± 0.24 °C, HR; -7 ± 8 b min^-1) and MENT (T_re; -0.23 ± 0.24 °C, HR; -4 ± 7 b min^-1).

CONCLUSION

The elderly have reduced physiological strain (T_re and HR) during activities of daily living and a 6MWT in hot UK climatic conditions, when they drink cold water. Furthermore, the elderly's perception (TS and TC) of the hot environment did not differ from CON at the end of exercise with COLD or MENT interventions. Menthol provided neither perceptual benefit to exercise in the heat nor functional gain. The TS data indicate that elderly may be at increased risk of heat illness, due to not feeling hot and uncomfortable enough to implement physiological strain reducing strategies such as cold-water ingestion.

If Motivation Was a Key Factor in Aerobic Performance in Tropical Climate?

This mini review examines the impact of tropical climate (TC) on motivational factors during aerobic performance and proposes the tracks of an integrative theoretical model to better understand the direct and indirect motivational mechanisms that can operate on athletic performances. TC is detrimental for aerobic performance and, although it clearly induces physiological constraints, these do not seem to be the only factors that explain the performance decline. Indeed, TC performance researchers have developed a theory of anticipation, which suggests that the brain commands a reduction in effort to protect the body from probable harm and heatstroke risk. The objective of this mini review is thus to examine the possibility that motivation may be a key factor in TC performance. The main psychological impacts of TC on aerobic performance are reviewed and an integrative theoretical model is presented that may help to better understand the mechanisms of motivation.

Perceptual and Physiological Responses to Carbohydrate and Menthol Mouth-Swilling Solutions: A Repeated Measures Cross-Over Preliminary Trial

Carbohydrate and menthol mouth-swilling have been used to enhance exercise performance in the heat. However, these strategies differ in mechanism and subjective experience. Participants (n = 12) sat for 60 min in hot conditions (35 °C; 15 ± 2%) following a 15 min control period, during which the participants undertook three 15 min testing blocks. A randomised swill (carbohydrate; menthol; water) was administered per testing block (one swill every three minutes within each block). Heart rate, tympanic temperature, thermal comfort, thermal sensation and thirst were recorded every three minutes. Data were analysed by ANOVA, with carbohydrate intake controlled for via ANCOVA. Small elevations in heart rate were observed after carbohydrate (ES: 0.22 ± 90% CI: −0.09–0.52) and water swilling (0.26; −0.04–0.54). Menthol showed small improvements in thermal comfort relative to carbohydrate (−0.33; −0.63–0.03) and water (−0.40; from −0.70 to −0.10), and induced moderate reductions in thermal sensation (−0.71; from −1.01 to −0.40 and −0.66; from −0.97 to −0.35, respectively). Menthol reduced thirst by a small to moderate extent. These effects persisted when controlling for dietary carbohydrate intake. Carbohydrate and water may elevate heart rate, whereas menthol elicits small improvements in thermal comfort, moderately improves thermal sensation and may mitigate thirst; these effects persist when dietary carbohydrate intake is controlled for.

Impact of elevated core temperature on cognition in hot environments within a military context

PURPOSE

Cognition can be impaired during exercise in the heat, potentially contributing to military casualties. To our knowledge, the independent role of elevated core temperature during exercise has not been determined. The aim of the current study was to evaluate effects of elevated core temperature on cognition during physically encumbering, heated exercise, and to determine whether the perceptual cooling effects of menthol preserves cognition.

METHODS

Eight participants complete three trials in randomised order: one normothermic (CON) and two with elevated (38.5°C) core temperature, induced by prior immersion in neutral versus hot water The CON trial and one hot trial (HOT) used a water mouth-rinse following each cognitive task of the trial, (HOT) while the other used a menthol mouth-rinse (MENT). Participants walked in humid heat (33°C, 75% relative humidity) in military clothing, completing a cognitive battery of reaction time, perceptual processing, working memory, executive function, cognitive flexibility, vigilance, and declarative memory.

RESULTS

No differences in cognitive performance were observed between any conditions. Near-infrared spectroscopy showed greater oxygenated haemoglobin tissue content in HOT and MENT compared to CON (ΔO₂Hb-deO₂Hb: 2.3 ± 4.5 µM, p < .024), and lower deoxygenated haemoglobin in MENT than in CON or HOT (p = .017), suggesting higher brain metabolism during the more stressful conditions.

CONCLUSION

Moderately elevated core (38.5°C) and skin temperature does not appear to impair cognitive performance during exercise despite mildly elevated cerebral metabolism. The effects of menthol remain undetermined due to the lack of heat-mediated cognitive impairment.

Development of a "Cooling" Menthol Energy Gel for Endurance Athletes: Effect of Menthol Concentration on Acceptability and Preferences

Menthol is effective at stimulating thermosensitive neurons that evoke pleasant cooling sensations. Internal application of menthol can be ergogenic for athletes, and hence, addition of menthol to sports nutrition products may be beneficial for athletes. The aim of this study was to develop a menthol energy gel for consumption during exercise and to determine acceptability and preferences for gels with different menthol concentrations. With a randomized, crossover, and double-blind placebo-controlled design, 40 endurance athletes (20 females) ingested an energy gel with a menthol additive at a high (0.5%; HIGH) or low concentration (0.1%; LOW), or a mint-flavored placebo (CON), on separate occasions during outdoor endurance training sessions. The athletes rated the gels for cooling sensation, mint flavor intensity, sweetness, and overall experience and provided feedback. Results are reported as median (interquartile range). Both menthol gels successfully delivered a cooling sensation, with a significantly greater response for HIGH (5.0 [4.0-5.0]) compared with LOW (3.5 [3.0-4.0]; p = .022) and CON (1.0 [1.0-2.0]; p < .0005), and LOW compared with CON (p < .0005). Ratings of mint flavor intensity followed the same trend as cooling sensation, while ratings of overall experience were significantly worse for HIGH (2.0 [1.0-3.0]) compared with LOW (4.0 [2.0-4.0]; p = .001) and CON (4.0 [3.0-4.0]; p < .0005). An energy gel with the addition of menthol at 0.1-0.5% provides a cooling sensation for athletes with a dose-response when ingested during exercise. The 0.1% concentration is recommended to maximize the overall experience of the gel.

Thermo-behavioural responses to orally applied l-menthol exhibit sex-specific differences during exercise in a hot environment

AIMS

This study investigated the efficacy of l-menthol mouth-rinsing on thermal sensation and perceived effort in females and males, using a fixed-rating of perceived exertion (RPE) exercise protocol in a hot environment.

METHODS

Twenty-two participants (eleven females, eleven males) completed two trials using a fixed-RPE protocol at an exercise intensity between 'hard' and 'very hard', equating to 16 on the RPE scale at ~35 °C. Participants adjusted power output to maintain RPE-16. In a randomised, double-blind, crossover design, l-menthol or a control mouthwash was administered at an orally neutral temperature (~32 °C) prior to exercise and at 10 min intervals thereafter. Measures of mechanical power output, core temperature, heart rate, perception of thermal sensation and thermal comfort, and whole-body sweat loss are reported.

RESULTS

Thermal sensation was lowered by l-menthol in both sexes (P < 0.05), however during exercise this was only maintained for 40% of the trial duration in females. Thermal comfort did not differ between conditions (P > 0.05). No differences in exercise duration were observed compared to control, despite a ~4% and ~6% increase in male and females respectively. Power output increased by ~6.5% males (P = 0.039) with no difference in females ~2.2% (P = 0.475), compared to control. Core temperature, heart rate and whole-body sweat loss was not different between condition or sex.

CONCLUSIONS

l-menthol lowered perceptual measures of thermal sensation in females, but did not attenuate a greater rate of rise in thermal sensitivity when exercising in a hot environment, compared to males. Males appeared to adopt a higher risk strategy by increasing power output following l-menthol administration in contrast to a more conservative pacing strategy in females. Therefore, there appear to be sex-specific differences in l-menthol's non-thermal cooling properties and subsequent effects on thermo-behavioural adjustments in work-load when exercising in a hot environment.

Menthol as an Ergogenic Aid for the Tokyo 2021 Olympic Games: An Expert-Led Consensus Statement Using the Modified Delphi Method

INTRODUCTION

Menthol topical application and mouth rinsing are ergogenic in hot environments, improving performance and perception, with differing effects on body temperature regulation. Consequently, athletes and federations are beginning to explore the possible benefits to elite sport performance for the Tokyo 2021 Olympics, which will take place in hot (~ 31 °C), humid (70% RH) conditions. There is no clear consensus on safe and effective menthol use for athletes, practitioners, or researchers. The present study addressed this shortfall by producing expert-led consensus recommendations.

METHOD

Fourteen contributors were recruited following ethical approval. A three-step modified Delphi method was used for voting on 96 statements generated following literature consultation; 192 statements total (96/96 topical application/mouth rinsing). Round 1 contributors voted to "agree" or "disagree" with statements; 80% agreement was required to accept statements. In round 2, contributors voted to "support" or "change" their round 1 unaccepted statements, with knowledge of the extant voting from round 1. Round 3 contributors met to discuss voting against key remaining statements.

RESULTS

Forty-seven statements reached consensus in round 1 (30/17 topical application/rinsing); 14 proved redundant. Six statements reached consensus in round 2 (2/4 topical application/rinsing); 116 statements proved redundant. Nine further statements were agreed in round 3 (6/3 topical application/rinsing) with caveats.

DISCUSSION

Consensus was reached on 62 statements in total (38/24 topical application/rinsing), enabling the development of guidance on safe menthol administration, with a view to enhancing performance and perception in the heat without impairing body temperature regulation.

Menthol can be safely applied to improve thermal perception during physical exercise: a meta-analysis of randomized controlled trials

Menthol is often used as a cold-mimicking substance to allegedly enhance performance during physical activity, however menthol-induced activation of cold-defence responses during exercise can intensify heat accumulation in the body. This meta-analysis aimed at studying the effects of menthol on thermal perception and thermophysiological homeostasis during exercise. PubMed, EMBASE, Cochrane Library, and Google Scholar databases were searched until May 2020. Menthol caused cooler thermal sensation by weighted mean difference (WMD) of - 1.65 (95% CI, - 2.96 to - 0.33) and tended to improve thermal comfort (WMD = 1.42; 95% CI, - 0.13 to 2.96) during physical exercise. However, there was no meaningful difference in sweat production (WMD = - 24.10 ml; 95% CI, - 139.59 to 91.39 ml), deep body temperature (WMD = 0.02 °C; 95% CI, - 0.11 to 0.15 °C), and heart rate (WMD = 2.67 bpm; 95% CI - 0.74 to 6.09 bpm) between the treatment groups. Menthol improved the performance time in certain subgroups, which are discussed. Our findings suggest that different factors, viz., external application, warmer environment, and higher body mass index can improve menthol's effects on endurance performance, however menthol does not compromise warmth-defence responses during exercise, thus it can be safely applied by athletes from the thermoregulation point of view.

Can taste be ergogenic?

Taste is a homeostatic function that conveys valuable information, such as energy density, readiness to eat, or toxicity of foodstuffs. Taste is not limited to the oral cavity but affects multiple physiological systems. In this review, we outline the ergogenic potential of substances that impart bitter, sweet, hot and cold tastes administered prior to and during exercise performance and whether the ergogenic benefits of taste are attributable to the placebo effect. Carbohydrate mouth rinsing seemingly improves endurance performance, along with a potentially ergogenic effect of oral exposure to both bitter tastants and caffeine although subsequent ingestion of bitter mouth rinses is likely required to enhance performance. Hot and cold tastes may prove beneficial in circumstances where athletes' thermal state may be challenged. Efficacy is not limited to taste, but extends to the stimulation of targeted receptors in the oral cavity and throughout the digestive tract, relaying signals pertaining to energy availability and temperature to appropriate neural centres. Dose, frequency and timing of tastant application likely require personalisation to be most effective, and can be enhanced or confounded by factors that relate to the placebo effect, highlighting taste as a critical factor in designing and administering applied sports science interventions.

Per-Cooling (Using Cooling Systems during Physical Exercise) Enhances Physical and Cognitive Performances in Hot Environments. A Narrative Review

There are many important sport events that are organized in environments with a very hot ambient temperature (Summer Olympics, FIFA World Cup, Tour de France, etc.) and in hot locations (e.g., Qatar). Additionally, in the context of global warming and heat wave periods, athletes are often subjected to hot ambient temperatures. It is known that exercising in the heat induces disturbances that may provoke premature fatigue and negatively affects overall performance in both endurance and high intensity exercises. Deterioration in several cognitive functions may also occur, and individuals may be at risk for heat illnesses. To train, perform, work and recover and in a safe and effective way, cooling strategies have been proposed and have been routinely applied before, during and after exercise. However, there is a limited understanding of the influences of per-cooling on performance, and it is the subject of the present review. This work examines the influences of per-cooling of different areas of the body on performance in terms of intense short-term exercises ("anaerobic" exercises), endurance exercises ("aerobic" exercises), and cognitive functioning and provides detailed strategies that can be applied when individuals train and/or perform in high ambient temperatures.

Menthol as an Adjuvant to Help Athletes Cope With a Tropical Climate: Tracks From Heat Experiments With Special Focus on Guadeloupe Investigations

Endurance and prolonged exercise are altered by hot climate. In hot and dry climate, thermoregulation processes, including evapotranspiration, normally maintain a relatively constant body core temperature. In hot and wet climate (usually called “tropical”), the decrease in evapotranspiration efficacy increases the sweating rate, which can rapidly induce severe hypohydration without efficiently reducing core temperature. The negative effects of tropical environment on long-duration exercise have been well documented, with clear demonstrations that they exceed the acclimation possibilities: both acclimated athletes and natives to tropical climate show impaired performances compared with that in neutral climate. New countermeasures, applicable during competitive events, are therefore needed to limit these negative effects. We studied the effects of several countermeasures in outdoor or natural tropical climates and noted that the easiest method to apply is cooling with cold (−1 to 3°C) beverage. Moreover, adding menthol increased the cold sensation induced by the beverage temperature, optimizing the positive effects on performance. We also demonstrated that efficient pre-cooling with cold menthol beverage requires drinking for 1 h instead of 30 min before the exercise. The optimal cooling method seems to be 1 h of cold + menthol pre-cooling ingestion followed by menthol + ice-slurry per-cooling. However, limitations should be noted: (1) the menthol concentration seems to be crucial, with positive effects for a 0.05% solution, whereas higher concentrations need to be explored; and (2) because it acts as a cold adjuvant without decreasing core temperature, menthol can lead to decreased thermoregulatory processes, thus inducing hyperthermia. Last, if menthol is added to cooling processes, athletes should first test them in training conditions for the maximal cooling effect to ensure optimal performance in competition in tropical climate.

Conventional and Alternative Strategies to Cope With the Subtropical Climate of Tokyo 2020: Impacts on Psychological Factors of Performance

The thermal discomfort caused by a hot or hot-wet climate can have negative effects on human performance. The 2020 Summer Olympic and Paralympic Games will take place in Tokyo’s hot and humid summer period, possibly exposing athletes to severe environmental stressors. In addition to technical, tactical, physical and nutritional preparation, Olympians and Paralympians need an optimal psychological state to turn in their best performances, especially in terms of emotional control, concentration and motivation. Yet, the tropical climate can have many negative effects on these factors. Better understanding of the negative effects of this climate and the strategies to manage them might be crucial for competitors, coaches and their teams in Japan. At the psychological level, cooling interventions before, during and/or immediately after exercise were mainly studied on perceptual responses. However, the effects of these interventions on other psychological components such as cognitive abilities or psychological states and the use of psychological techniques have been little explored, especially in hot-wet climate. Thus, this article proposes to take stock of the knowledge on the conventional and alternative strategies that help athletes to psychologically cope with the subtropical climate of Tokyo.

Intermittent sprint performance in the heat is not altered by augmenting thermal perception via L-menthol or capsaicin mouth rinses

Purpose

Cooling sensations elicited by mouth rinsing with L-menthol have been reported as ergogenic. Presently, responses to L-menthol mouth rinsing during intermittent sprint performance (ISP) in the heat are unknown and the impact of increased thermal perception on ISP via capsaicin has also not been quantified. This experiment aimed to identify whether eliciting cooling/warming sensations via L-menthol/capsaicin would alter ISP in the heat.

Method

Fourteen participants (mass = 72 ± 9 kg, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot {V}{{\text{O}}_{2{\text{peak}}}}$$\end{document}V˙O2peak = 3.30 ± 0.90 L min⁻¹), undertook four experimental trials, involving 40 min of ISP in hot conditions (40.2 ± 0.6 °C, 42 ± 2% R.H.) with mouth rinsing (25 mL, 6 s) at the protocol onset, and every 10 min thereafter. Cooling (0.01% L-menthol; MEN), warming (0.2% capsaicin; CAP), placebo (0.3 sham-CHO; PLA), and control (water; CON) mouth rinses were utilized. Performance was quantified via power (PP) and work done (WD) during sprints. Heart rate (HR), core (T_rec) and skin (T_skin) temperature, perceived exertion (RPE), thermal sensation (T_sens), and comfort (T_com) were measured at 10 min intervals. Sweat rate (whole-body sweat rate) was calculated from ∆mass.

Result

PP reduced over time (P < 0.05); however, no change was observed between trials for PP or WD (P > 0.05). T_com increased over time and was lower in MEN (2.7 ± 1.1; P < 0.05) with no difference between CAP (3.1 ± 1.2), PLA (3.2 ± 1.3) and CON (3.1 ± 1.3). RPE, T_sens HR, T_rec, and T_skin increased over time (P < 0.05) with no between trial differences (P > 0.05).

Conclusion

Despite improved thermal comfort via L-menthol, ISP did not improve. Capsaicin did not alter thermal perception or ISP. The reduction in ISP over time in hot conditions is not influenced by thermal perception.

Electronic supplementary material

The online version of this article (10.1007/s00421-018-4055-0) contains supplementary material, which is available to authorized users.

Endurance Performance is Influenced by Perceptions of Pain and Temperature: Theory, Applications and Safety Considerations

Models of endurance performance now recognise input from the brain, including an athlete's ability to cope with various non-pleasurable perceptions during exercise, such as pain and temperature. Exercise training can reduce perceptions of both pain and temperature over time, partly explaining why athletes generally have a higher pain tolerance, despite a similar pain threshold, compared with active controls. Several strategies with varying efficacy may ameliorate the perceptions of pain (e.g. acetaminophen, transcranial direct current stimulation and transcutaneous electrical stimulation) and temperature (e.g. menthol beverages, topical menthol products and other cooling strategies, especially those targeting the head) during exercise to improve athletic performance. This review describes both the theory and practical applications of these interventions in the endurance sport setting, as well as the potentially harmful health consequences of their use.

Immersion with menthol improves recovery between 2 cycling exercises in hot and humid environment

Endurance exercise performance is impaired in a hot and humid environment. This study compared the effects of cold water immersion, with (CMWI) and without (CWI) menthol, on the recovery of cycling performance. Eight heat-acclimatized cyclists (age, 24.1 ± 4.4 years; mass, 65.3 ± 5.2 kg) performed 2 randomized sessions, each consisting of a 20-min cycling trial (T1) followed by 10 min of immersion during recovery and then a second 20-min cycling trial (T2). Mean power output and perceived exertion (RPE) were recorded for both trials. Rectal (Trec) and skin temperatures were measured before and immediately after T1, immersion, and T2. Perceived thermal sensation (TS) and comfort were measured immediately after T1 and T2. Power output was significantly improved in T2 compared with T1 in the CMWI condition (+15.6%). Performance did not change in the CWI condition. After immersion, Trec was lower in CWI (–1.17 °C) than in CMWI (–0.6 °C). TS decreased significantly after immersion in both conditions. This decline was significantly more pronounced in CMWI (5.9 ± 1 to 3.6 ± 0.5) than in CWI (5.6 ± 0.9 to 4.4 ± 1.2). In CMWI, RPE was significantly higher in T1 (6.57 ± 0.9) than in T2 (5.14 ± 1.25). However, there was no difference in TC. This study suggests that menthol immersion probably (i) improves the performance of a repeated 20-min cycling bout, (ii) decreases TS, and (iii) impairs thermoregulation processes.

Lower-Limb Passive Heat Maintenance Combined With Pre-cooling Improves Repeated Sprint Ability

Pre-conditioning strategies to potentiate performance are a common feature of pre-competition routines. The elevation of muscle temperature is seen as a vital component of preparing for physical performance, while pre-cooling strategies have been adopted to offset fatigue during repeated efforts. We investigated the individual and combined effects of a passive heat maintenance strategy and the ingestion of an ice-water slurry on repeated sprint performance. In a random cross-over design, 12 professional male athletes performed 5 × 40 m maximal running sprints under one of four conditions following a standardized warm-up: 15-min passive rest (Control); wearing a lower-body survival garment (HEAT); consuming a 500 mL ice slushy (COLD); or wearing the survival garment and consuming the slushy (H+C). Measures of sprint speed, fatigue, heart rate, and rectal temperature were collected. Compared to COLD: HEAT improved Sprint 1 (ES: 0.84; p = 0.05), but negatively impacted Sprint 4 (ES: -0.87; p = 0.08), and Sprint 5 (ES: -1.57; p = 0.002). H+C was faster than Control for every sprint (ES: 0.28 to 0.66), clearly faster than COLD on Sprints 1–3 (ES: 0.73 to 0.54), and clearly faster than HEAT on Sprints 4 and 5 (ES: 1.31 and 1.87). Fatigue was greatest after the HEAT intervention with a large correlation between fatigue and rectal temperature (r = 0.66; p = 0.0204). While there are undoubtedly peripheral effects of cooling and heating on various aspects of muscle function and fatigue, understanding the integration of psychophysiological homeostatic feedback loops relating to a combined warming and cooling intervention may benefit sports in which repeat sprints are performed.

L-Menthol mouth rinse or ice slurry ingestion during the latter stages of exercise in the heat provide a novel stimulus to enhance performance despite elevation in mean body temperature

Purpose

This study investigated the effects of l-menthol mouth rinse and ice slurry ingestion on time to exhaustion, when administered at the latter stages (~ 85%) of baseline exercise duration in the heat (35 °C).

Method

Ten male participants performed four time to exhaustion (TTE) trials on a cycle ergometer at 70% W_max. In a randomized crossover design, (1) placebo-flavored non-calorific mouth rinse, (2) l-menthol mouth rinse (0.01%), or (3) ice ingestion (1.25 g kg⁻¹), was administered at 85% of participants’ baseline TTE. Time to exhaustion, core and skin temperature, heart rate, rating of perceived effort, thermal comfort and thermal sensation were recorded.

Results

From the point of administration at 85% of baseline TTE, exercise time was extended by 1% (placebo, 15 s), 6% (l-menthol, 82 s) and 7% (ice, 108 s), relative to baseline performance (P = 0.036), with no difference between l-menthol and ice (P > 0.05). Core temperature, skin temperature, and heart rate increased with time but did not differ between conditions (P > 0.05). Thermal sensation did not differ significantly but demonstrated a large effect size (P = 0.080; \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\eta _{{\text{p}}}^{2}$$\end{document}ηp2 = 0.260).

Conclusion

These results indicate that both thermally cooling and non-thermally cooling oral stimuli have an equal and immediate behavioral, rather than physiological, influence on exhaustive exercise in the heat.