Oral application of L-menthol in the heat: From pleasure to performance

When menthol is applied to the oral cavity it presents with a familiar refreshing sensation and cooling mint flavour. This may be deemed hedonic in some individuals, but may cause irritation in others. This variation in response is likely dependent upon trigeminal sensitivity toward cold stimuli, suggesting a need for a menthol solution that can be easily personalised. Menthol’s characteristics can also be enhanced by matching colour to qualitative outcomes; a factor which can easily be manipulated by practitioners working in athletic or occupational settings to potentially enhance intervention efficacy. This presentation will outline the efficacy of oral menthol application for improving time trial performance to date, either via swilling or via co-ingestion with other cooling strategies, with an emphasis upon how menthol can be applied in ecologically valid scenarios. Situations in which performance is not expected to be enhanced will also be discussed. An updated model by which menthol may prove hedonic, satiate thirst and affect ventilation will also be presented, with the potential performance implications of these findings discussed and modelled. Qualitative reflections from athletes that have implemented menthol mouth swilling in competition, training and maximal exercise will also be included

The effectiveness of orally applied L-menthol on exercise performance in the heat

During exercise in the heat, increasing thermal load leads to thermo-behavioural adjustments in exercise performance, due to greater perceptual and physiological strain. Behavioural reductions in exercise intensity in the heat are initially mediated via rises in skin temperature, which alter thermal perception (comfort and sensation) and later by rises in core temperature, which increase cardiovascular strain and perceived exertion. Therefore, thermoregulation may be ordered and dependant on the magnitude, timing and/or prioritisation of afferent signals. Non-thermal cooling via L-menthol has been shown to enhance exercise performance in the early and latter stages when delivered orally at a concentration of 0.01%. Indeed, during periods of progressive thermal stress, imposed by the combination of maximal exercise and environmental heat and humidity, L-menthol has been shown to offer an immediate cooling stimulus thus extending exercise capacity. However, repeated administration of L-menthol during exercise in the heat, as thermal load increases, is unable to recover a decline in work rate. Therefore, it is unclear whether the potency of L-menthol is sustained upon frequent application and what strategies are needed in both sporting and occupational settings to optimise its effectiveness. In this part of the symposium we will consider oral delivery of L-menthol and its potential for reducing an individual’s perception of heat stress with associated effects on exercise tolerance in the heat. We will also examine the frequency of use, optimal concentration, timing and novelty of L-menthol in a sporting and occupational context

Palmitoylation of BK channels

Palmitoylation is a post-translational modification that has been implicated in the control of multiple proteins, including ion channels. S-Palmitoylation is a lipophilic modification that involves the attachment of palmitate through a thioester linkage to a cysteine residue in a target protein. By increasing the hydrophobicity of the target region, palmitoylation can promote membrane targeting. Here, palmitoylation is shown to play an important role in regulating large conductance calcium- and voltage- activated (BK) potassium channels. The STREX splice variant of the BK channel contains a 58 amino acid insert at the splice site C2 within the intracellular C-terminal RCK1-RCK2 linker that confers increased calcium sensitivity to the channel and determines PKA inhibition of channel activity. The cysteine rich STREX domain was predicted to be palmitoylated, and using an imaging assay STREX was shown to act as a membrane targeting domain through palmitoylation of a di-cysteine motif (C645:C645). A membrane potential assay and electrophysiological analysis demonstrates that palmitoylation at the C645:C646 site in STREX is important in mediating the increased calcium sensitive properties inherent to the STREX channel. Palmitoylation is also shown to modulate PKA channel inhibition. The stability of palmitoylation can often be reliant on the local environment within the protein. Generally in most proteins; lipidated regions, basic domains or transmembrane domains are found adjacent to a palmitoylation site. In STREX, a polybasic domain composed of 11 basic residues just upstream from the C645:C646 palmitoylation site, functions to control the palmitoylation status of the STREX insert. A site directed mutagenesis approach to disrupt the polybasic domain revealed an important role in controlling membrane targeting of the STREX C-terminus, mediating the increased calcium sensitivity inherent to STREX channels and controlling the palmitoylation status of the C645:C646 palmitoylation site using multiple techniques involving electrophysiology, fluorescent imaging and biochemical assays. Further to this, using imaging to examine the membrane association of fluorescently tagged C-terminal proteins, phosphorylation is shown to function as a physiological electrostatic switch to regulate the polybasic region in controlling palmitoylation of the STREX insert. Finally, an additional palmitoylation site that is constitutively expressed in all BK channels was identified to be located in the S0-S1 linker (C53:C54:C56). Mutation of the C53:C54:C56 palmitoylation site in the S0-S1 linker was shown to abolish all palmitoylation in BK channels that did not contain the STREX insert. Palmitoylation allows the S0-S1 linker to associate with the plasma membrane however the mutated de-palmitoylated channels did not affect channel conductance or the calcium/voltage sensitivity of the channel. Palmitoylation of the S0-S1 linker was shown to be a critical determinant of cell surface expression of BK channels, as steady state surface expression levels were reduced by ~55% in the C53:C54:C56 mutant. STREX channels that could not be palmitoylated in the S0-S1 linker also showed decreased surface expression even through STREX insert palmitoylation was unaffected. Palmitoylation is rapidly emerging as an important post-translational mechanism to control ion channel behaviour. This work reveals that palmitoylation of the BK channel can control channel function of the STREX splice variant channel and can regulate cell surface expression in all other channel variants. Palmitoylation appears to be functionally independent at these two distinct sites expressed within the same channel protein

Oral taurine improves critical power and severe-intensity exercise tolerance

This study investigated the effects of acute oral taurine ingestion on: (1) the power–time relationship using the 3-min all-out test (3MAOT); (2) time to exhaustion (TTE) 5% > critical power (CP) and (3) the estimated time to complete (Tlim) a range of fixed target intensities. Twelve males completed a baseline 3MAOT test on a cycle ergometer. Following this, a double-blind, randomised cross-over design was followed, where participants were allocated to one of four conditions, separated by 72 h: TTE + taurine; TTE + placebo; 3MAOT + taurine; 3MAOT + placebo. Taurine was provided at 50 mg kg−1, whilst the placebo was 3 mg kg−1 maltodextrin. CP was higher (P  0.05), yet TTE 5% > CP increased (P < 0.05) by 1.7 min after taurine (17.7 min) compared to placebo (16.0 min) and there were higher (P < 0.001) estimated Tlim across all work targets. Acute supplementation of 50 mg kg−1 of taurine improved CP and estimated performance at a range of severe work intensities. Oral taurine can be taken prior to exercise to enhance endurance performance

The application of menthol in sport, exercise and occupational settings: To apply, ingest or discard?

The cold-receptor agonist menthol has been utilised to improve performance by imparting feelings of coolness and freshness to alleviate thermal discomfort. These effects are mediated by peripheral cold-sensitive neurons and trigeminal nerves of the face and oral cavity via activation of TRPM8 channels by either applying, ingesting or swilling menthol solutions. The forcing function exerted by topically applied menthol is probably influenced by a combination of factors, including the percentage of body surface area (BSA) exposed, body region, and dose, but the weighting of each requires clarification, as do factors influencing oral administration. Topically, a greater menthol-mediated forcing function has been shown to alter thermoregulation resulting in heat gain, but the precise mechanisms require clarification. It is unknown whether there is a similar effect when menthol is administered orally, but higher concentrations are reportedly preferred. Consequently, menthol has the potential to improve thermal perception but evoke heat gain responses placing biophysical and behavioural thermoregulation in conflict. Nevertheless, there is a growing body of literature that supports the efficacy of menthol application to improve endurance performance and, more recently, muscular performance. Oral menthol application has been shown to improve time to exhaustion and time trial performance with emerging evidence in power based activities. Independently of the heat storage response, topically applied menthol has also been shown to improve endurance performance and enhance recovery from exercise-induced muscle damage, possibly due to increased motor unit activation. Both methods of application have consistently been shown to ameliorate subjective measures of thermal strain during exercise. Accordingly, the aim of this symposium is to present key literature on the perceptual, thermoregulatory and performance effects of menthol and actively debate the merits of: the medium of application, advised protocols for menthol use during these modalities, the timing of application and the resultant thermoregulatory effects

Narratives of access: A critical exploration of how institutional interactions with students affect regional student participation in higher education.

This article examines the narratives that drive university staff understanding of the concerns and experiences of regional and remote students at five universities in Australia. Interviews were conducted with thirty university staff members over a period of three months in 2018. Reflexive thematic analysis of the stories told by staff of supporting regional students found that staff used the lens of access to create meaningful stories for themselves and others in how they supported students. Access is defined as a multi-faceted term encompassing access to people, Internet, study materials and equipment and study environments. Access is facilitated by a sense of belonging or identity as a student and limited by the lack of this. Our analysis of “belongingness” draws on Bourdieu’s concepts of habitas to start to unpick the interactions between higher education institutions and the student that develop student identities as scholars and centres the narrative on the student as a person, wrestling to gain many forms of access within complex social situations

Physiological and thermoregulatory effects of oral taurine supplementation on exercise tolerance during forced convective cooling

We investigated the effects of taurine supplementation on cycling time to exhaustion in cold conditions. Eleven males cycled to exhaustion at a power output equivalent to the mid-point between ventilatory threshold and maximum aerobic power following 15-min rest in the cold (apparent temperature of ∼ 4 °C; air flow of 4.17 m·s-1). Two-hours before, participants ingested taurine (50 mg·kg-1) or placebo beverage. Pulmonary gases, carbohydrate (CHO) and fat oxidation, body temperatures, mean local sweat rate, heart rate, rate of perceived exertion (RPE) and thermal comfort were recorded. Time to exhaustion was not different between trials (taurine = 14.6 ± 4.7 min; placebo = 13.4 ± 5.6 min, P = 0.061, d = 0.27). There were no effects (P > 0.05) of taurine on core temperature, mean skin temperature or local sweat rates. However, the placebo condition showed greater (P < 0.05) reductions in arm-to-finger temperature gradient (i.e. vasodilation) across pre-exercise passive cold exposure and increased CHO oxidation (P < 0.05). Participants also reached a thermally ‘comfortable’ level quicker in the taurine condition (P < 0.05). A 50 mg·kg-1 dose of taurine did not statistically benefit endurance exercise after moderate cold exposure but conferred some potential vascular and metabolic effects

Caffeine and sprint cycling performance: effects of torque factor and sprint duration

Purpose: The aim of this study was to investigate the influence of torque factor and sprint duration on the effects of caffeine on sprint cycling performance. Methods: Using a counterbalanced, randomized, double-blind, placebo-controlled design, 13 men completed nine trials. In Trial 1, participants completed a series of 6 s sprints at increasing torque factors, to determine the torque factor, for each individual, which elicited the highest (TOPTIMAL) peak power output (PPO). The remaining trials involved all combinations of torque factor (0.8 N∙m∙kg-1 versus TOPTIMAL), sprint duration (10 s versus 30 s), and supplementation (caffeine [5mg∙kg-1] versus placebo). Results: There was a significant effect of torque factor on PPO, with higher values at TOPTIMAL (mean difference: 168 W; 95% likely range: 142 – 195 W). There was also a significant effect of sprint duration on PPO, with higher values in 10 s sprints (mean difference: 52 W; 95% likely range: 18 – 86 W). However, there was no effect of supplementation on PPO (p = 0.056). Nevertheless, there was a significant torque factor × sprint duration × supplement interaction (p = 0.036), with post hoc tests revealing that caffeine produced a higher PPO (mean difference: 76 W; 95% likely range: 19 – 133 W) when the sprint duration was 10 s and the torque factor was TOPTIMAL. Conclusions: The results of this study show that when torque factor and sprint duration are optimized, to allow participants to express their highest PPO, there is a clear effect of caffeine on sprinting performance

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% Wmax. 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; [Formula: see text] = 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