The influence of a menthol and ethanol soaked garment on human temperature regulation and perception during exercise and rest in warm, humid conditions.

UNLABELLED: This study assessed whether donning a garment saturated with menthol and ethanol (M/E) can improve evaporative cooling and thermal perceptions versus water (W) or nothing (CON) during low intensity exercise and rest in warm, humid conditions often encountered in recreational/occupational settings. It was hypothesised there would be no difference in rectal (Tre) and skin (Tsk) temperature, infra-red thermal imagery of the chest/back, thermal comfort (TC) and rating of perceived exertion (RPE) between M/E, W and CON, but participants would feel cooler in M/E versus W or CON. METHODS: Six volunteers (mean [SD] 22 [4] years, 72.4 [7.4] kg and 173.6 [3.7] cm) completed (separate days) three, 60-min tests in 30°C, 70%rh, in a balanced order. After 15-min of seated rest participants donned a dry (CON) or 80mL soaked (M/E, W) long sleeve shirt appropriate to their intervention. They then undertook 30-min of low intensity stepping at a rate of 12steps/min on a 22.5cm box, followed by 15-min of seated rest. Measurements included heart rate (HR), Tre, Tsk (chest/back/forearm), thermal imaging (back/chest), thermal sensation (TS), TC and RPE. Data were reported every fifth minute as they changed from baseline and the area under the curves were compared by condition using one-way repeated measures ANOVA, with an alpha level of 0.05. RESULTS: Tre differed by condition, with the largest heat storage response observed in M/E (p<0.05). Skin temperature at the chest/back/forearm, and thermal imaging of the chest all differed by condition, with the greatest rate of heat loss observed in W and M/E respectively (p<0.01). Thermal sensation differed by condition, with the coolest sensations observed in M/E (p<0.001). No other differences were observed. CONCLUSIONS: Both M/E and W enhanced evaporative cooling compared CON, but M/E causes cooler sensations and a heat storage response, both of which are likely mediated by menthol.

Relieving thermal discomfort: Effects of sprayed L-menthol on perception, performance, and time trial cycling in the heat.

L-menthol stimulates cutaneous thermoreceptors and induces cool sensations improving thermal comfort, but has been linked to heat storage responses; this could increase risk of heat illness during self-paced exercise in the heat. Therefore, L-menthol application could lead to a discrepancy between behavioral and autonomic thermoregulatory drivers. Eight male participants volunteered. They were familiarized and then completed two trials in hot conditions (33.5 °C, 33% relative humidity) where their t-shirt was sprayed with CONTROL-SPRAY or MENTHOL-SPRAY after 10 km (i.e., when they were hot and uncomfortable) of a 16.1-km cycling time trial (TT). Thermal perception [thermal sensation (TS) and comfort (TC)], thermal responses [rectal temperature (Trec ), skin temperature (Tskin )], perceived exertion (RPE), heart rate, pacing (power output), and TT completion time were measured. MENTHOL-SPRAY made participants feel cooler and more comfortable and resulted in lower RPE (i.e., less exertion) yet performance was unchanged [TT completion: CONTROL-SPRAY 32.4 (2.9) and MENTHOL-SPRAY 32.7 (3.0) min]. Trec rate of increase was 1.40 (0.60) and 1.45 (0.40) °C/h after CONTROL-SPRAY and MENTHOL-SPRAY application, which were not different. Spraying L-menthol toward the end of self-paced exercise in the heat improved perception, but did not alter performance and did not increase heat illness risk.

Physiological cost and thermal envelope: a novel approach to cycle garment evaluation during a representative protocol.

This study aimed to examine thermoregulation in different clothing assemblies during a representative cycling exercise protocol. Six men undertook cycling exercise simulating representative thermal exchange challenges while wearing low (LOW), intermediate (INT1 and INT2), or high (HI) amounts of clothing. Exercise was conducted at 14.5 °C, 46.8% relative humidity and included a "flat" [45 min at 35% peak power output (PPO), wind speed 8.3 m/s], "uphill" (30 min at 55% PPO, wind speed 3.6 m/s), and "downhill" (20 min at 50 W, wind speed 16.7 m/s) stage. Rectal temperature changed with the exercise stage and was independent of clothing assembly. In contrast, an "envelope" was evident for mean body temperature, resulting from differences in mean skin temperature between the LOW and HI conditions. The elevated mean body temperature in HI was associated with increased physiological "cost," in the form of increased sweat production and heart rate. Physiological cost provides a better index of clothing performance than deep body temperature in the "thermoregulatory zone," as a consequence sports clothing should attempt to optimize the balance between comfort and reduced physiological cost.

Augmented supraspinal fatigue following constant-load cycling in the heat.

The development of central fatigue is prominent following exercise-induced hyperthermia, but the contribution of supraspinal fatigue is not well understood. Seven endurance-trained cyclists (mean ± SD peak O2 uptake, 62.0 ± 5.6 mL/kg/min) completed two high-intensity constant-load cycling trials (296 ± 34 W) to the limit of tolerance in a hot (34 °C, 20% relative humidity) and, on a separate occasion, for the same duration, a control condition (18 °C, 20% relative humidity). Core body temperature (Tc ) was measured throughout. Before and immediately after each trial, twitch responses to supramaximal femoral nerve and transcranial magnetic stimulation were obtained from the knee extensors to assess neuromuscular and corticospinal function, respectively. Exercise time was 11.4 ± 2.6 min. Peak Tc was higher in the hot compared with control (38.36 ± 0.43 °C vs 37.86 ± 0.36 °C; P = 0.035). Post-exercise reductions in maximal voluntary contraction force (13 ± 9% vs 9 ± 5%), potentiated twitch force (16 ± 12% vs 21 ± 13%) and voluntary activation (9 ± 7% vs 7 ± 7%) were similar in hot and control trials, respectively. However, cortical voluntary activation declined more in the hot compared with the control (8 ± 3% vs 3 ± 2%; P = 0.001). Exercise-induced hyperthermia elicits significant central fatigue of which a large portion can be attributed to supraspinal fatigue. These data indicate that performance decrements in the heat might initially originate in the brain.

Spraying with 0.20% L-menthol does not enhance 5 km running performance in the heat in untrained runners.

BACKGROUND: L-Menthol stimulates cutaneous thermoreceptors and induces cool sensations improving thermal comfort but has also been linked to heat storage responses. Therefore, L-Menthol application could lead to a conflict in behavioural and thermoregulatory drivers improving comfort but leading to a higher rate of deep body temperature rise; the present study examined this possibility. METHODS: Six untrained male participants (age 21 [1] years; height 1.80 [0.07] m; mass 78.9 [6.9] kg; surface area 1.98 [0.13] m2) took part. They completed three trials in hot conditions (34 °C) where their clothing was sprayed (CONTROL-SPRAY or MENTHOL-SPRAY) or not sprayed (CONTROL) after a fixed intensity exercise period (15-minutes), which induced thermal discomfort, before completing a 5 km treadmill time trial (TT). Thermal perception (thermal sensation and comfort; TS, TC), thermal responses (aural temperature [Tau], skin temperature [Tskin]), perceived exertion (RPE), heart rate, pacing (1 km split time) and performance (TT completion time) were measured. RESULTS: MENTHOL-SPRAY induced improvements in TS (up to 3 km of TT) and TC (up to 1 km) with Tau showing a tendency to be higher than CONTROL-SPRAY (+0.20 [0.29] °C) and CONTROL condition (0.30 [0.34] °C); this was not statistically significant and the rate of rise in Tau was linear. Tau was continuing to rise between the 4th and 5th kilometre of the TT. The other variables were unchanged. TT completion time and pace were not different: CONTROL 27.92 [1.65], CONTROL-SPRAY 28.10 [1.12], MENTHOL-SPRAY 27.53 [2.85] minutes. CONCLUSION: Spraying L-MENTHOL prior to exercise in the heat culminated in improved perception but not altered performance.

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.

Effect of task familiarisation on distribution of energy during a 2000 m cycling time trial.

AIM: To investigate the effect of task familiarisation on the spontaneous pattern of energy expenditure during a series of 2000 m cycling time trials (TTs). METHOD: Nine trained males completed three 2000 m TTs on a Velotron cycling ergometer. To examine pacing strategy, the data were assigned to 250 m "bins," with the pattern of aerobic and anaerobic energy expenditure calculated from total work accomplished and gas-exchange data. RESULTS: There were no significant differences between trials in performance times (191.4 (SD 4.3), 189.4 (4.6), 190.1 (5.6) s), total aerobic (58.3 (2.7), 58.4 (3.1), 58.0 (3.4) kJ) and total anaerobic energy expenditure (16.4 (3.3), 17.3 (2.8), 16.5 (3.1) kJ). Pacing strategy in the second and third TT differed from the first TT in that a lower power output was adopted during the first 500 m, enabling a higher power output during the final 750 m of the TT. This adjustment in the pattern of energy expenditure was mediated by an alteration in the pattern of anaerobic energy expenditure, which paralleled changes in total energy expenditure. Furthermore, participants retained an anaerobic energy "reserve" enabling an end-spurt during the second and third trials. CONCLUSION: Small modifications to the pacing strategy are made following a single bout of exercise, primarily by altering the rate of anaerobic energy expenditure. This may have served to prevent critical metabolic disturbances. The alteration in pacing strategy following the first exercise bout is compatible with a complex intelligent regulatory system.

Neuromuscular changes and the rapid adaptation following a bout of damaging eccentric exercise.

INTRODUCTION: An initial bout of eccentric exercise is known to protect against muscle damage following a repeated bout of the same exercise; however, the neuromuscular adaptations owing to this phenomenon are unknown. AIM: To determine whether neuromuscular disturbances are modulated following a repeated bout of eccentric exercise. METHODS: Following eccentric exercise performed with the elbow flexors, we measured maximal voluntary force, resting twitch force, muscle soreness, creatine kinase (CK) and voluntary activation (VA) using motor point and motor cortex stimulation at baseline, immediately post-exercise and at 1, 2, 3, 4 and 7 days post-exercise on two occasions, separated by 3 weeks. RESULTS: Significant muscle damage and fatigue were evident following the first exercise bout; maximal voluntary contraction (MVC) was reduced immediately by 35% and remained depressed at 7 days post-exercise. Soreness and CK release peaked at 3 and 4 days post-exercise respectively. Resting twitch force remained significantly reduced at 7 days (-48%), whilst VA measured with motor point and motor cortex stimulation was reduced until 2 and 3 days respectively. A repeated bout effect (RBE) was observed with attenuated soreness and CK release and a quicker recovery of MVC and resting twitch force. A similar decrement in VA was observed following both bouts; however, following the repeated bout there was a significantly smaller reduction in, and a faster recovery of, VA measured using motor cortical stimulation. CONCLUSION: Our data suggest that the RBE may be explained, partly, by a modification in motor corticospinal drive.

Barefoot running improves economy at high intensities and peak treadmill velocity.

AIM: Barefoot running can improve running economy (RE) compared to shod running at low exercise intensities, but data is lacking for the higher intensities typical during many distance running competitions. The influence of barefoot running on the velocity at maximal oxygen uptake (vVO2max) and peak incremental treadmill test velocity (vmax) is unknown. The present study tested the hypotheses that barefoot running would improve RE, vVO2max and vmax relative to shod running. METHODS: Using a balanced within-subject repeated measures design, eight male runners (aged 23.1±4.5 years, height 1.80±0.06 m, mass 73.8±11.5 kg, VO2max 4.08±0.39 L·min(-1)) completed a familiarization followed by one barefoot and one shod treadmill running trial, 2-14 days apart. Trial sessions consisted of a 5 minute warm-up, 5 minute rest, followed by 4×4 minute stages, at speeds corresponding to ~67, 75, 84 and 91% shod VO2max respectively, separated by a 1 minute rest. After the 4th stage treadmill speed was incremented by 0.1 km·h(-1) every 15 s until participants reached volitional exhaustion. RESULTS: RE was improved by 4.4±7.0% across intensities in the barefoot condition (P=0.040). The improvement in RE was related to removed shoe mass (r2=0.80, P=0.003) with an intercept at 0% improvement for RE at 0.520 kg total shoe mass. Both vVO2max (by 4.5±5.0%, P=0.048) and vmax (by 3.9±4.0%, P=0.030) also improved but VO2max was unchanged (p=0.747). CONCLUSION: Barefoot running improves RE at high exercise intensities and increases vVO2max and vmax, but further research is required to clarify the influence of very light shoe weights on RE.