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

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

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 effect of carbohydrate ingestion on the Interleukin-6 response to a 90-minute run time trial

Fatigue is a predictable outcome of prolonged physical activity; yet its biological cause remains uncertain. During exercise, a polypeptide messenger molecule interleukin- 6 (IL-6) is actively produced. Previously, it has been demonstrated that administration of recombinant IL-6 (rhIL-6) impairs 10-km run performance and heightened sensation of fatigue in trained runners. Both high carbohydrate diets and carbohydrate ingestion during prolonged exercise have a blunting effect on IL-6 levels postendurance exercise. We hypothesized that carbohydrate ingestion may improve performance during a prolonged bout of exercise as a consequence of a blunted IL-6 response. Seven recreationally trained fasted runners completed two 90-min time trials under CHO supplemented and placebo conditions in a randomized order. The study was of a double-blinded, placebo-controlled, cross-over study design. Distance covered in 90 min was significantly greater following exogenous carbohydrate ingestion compared with the placebo trial (19.13 ± 1.7 km and 18.29 ± 1.9 km, respectively, p = .0022). While postexercise IL-6 levels were significantly lower in the CHO trial compared with the placebo trial (5.3 ± 1.9 pg·mL?1and 6.6 ± 3.0 pg·mL?1, respectively; p = .0313), this difference was considered physiologically too small to mediate the improvement in time trial performance

Inherent work suit buoyancy distribution:effects on lifejacket self-righting performance

Introduction: Accidental immersion in cold water is an occupational risk. Work suits and life jackets (LJ) should work effectively in combination to keep the airway clear of the water (freeboard) and enable self-righting. We hypothesized that inherent buoyancy, in the suit or LJ, would be beneficial for enabling freeboard, but its distribution may influence LJ self-righting. Methods: Six participants consented to complete nine immersions. Suits and LJ tested were: flotation suit (FLOAT; 85 N inherent buoyancy); oilskins 1 (OS-1) and 2 (OS-2), both with no inherent buoyancy; LJs (inherent buoyancy/buoyancy after inflation/total buoyancy), LJ-1 50/150/200 N, LJ-2 0/290/290 N, LJ-3 80/190/270 N. Once dressed, the subject entered an immersion pool where uninflated freeboard, self-righting performance, and inflated freeboard were measured. Data were compared using Friedman’s test to the 0.05 alpha level. Results: All suits and LJs enabled uninflated and inflated freeboard, but differences were seen between the suits and LJs. Self-righting was achieved on 43 of 54 occasions, irrespective of suit or LJ. On all occasions that self-righting was not achieved, this occurred in an LJ that included inherent buoyancy (11/54 occasions). Of these 11 failures, 8 occurred (73% of occasions) when the FLOAT suit was being worn. Discussion: LJs that included inherent buoyancy, that are certified as effective on their own, worked less effectively from the perspective of self-righting in combination with a work suit that also included inherent buoyancy. Equipment that is approved for use in the workplace should be tested in combination to ensure adequate performance in an emergency scenario

Enhancement of Exercise Capacity in the Heat With Repeated Menthol-Spray Application

Purpose Exercise performance is impaired in the heat and a contributing factor to this decrement is thermal discomfort. Menthol-spraying of skin is one means of alleviating thermal discomfort but has yet to be shown to be ergogenic using single spray applications. We examined whether repeated menthol-spraying could relieve thermal discomfort, reduce perception of exertion and improve exercise performance in hot (35ºC), dry (22% RH) conditions; we hypothesised it would. Method Eight trained cyclists completed two separate conditions of fixed intensity (FI) cycling (50% PMax) for 45-minutes before a test to exhaustion (TTE; 70% PMax) with 100 mL of menthol-spray (0.20% menthol) or control-spray applied to the torso after 20 and 40-minutes. Perceptual (thermal sensation (TS), thermal comfort (TC), RPE) performance (TTE duration), thermal variables (skin temperature (Tskin), rectal temperature (Trec), cardiac frequency (fc)) and sweating were measured. Data were compared using ANOVA to 0.05 alpha level. Results Menthol-spray improved TS (‘cold’ sensation cf ‘warm/hot’ after first spraying; p=.008) but only descriptively altered TC (‘comfortable’ cf ‘uncomfortable’; p=.173). Sweat production (994 (380) mL cf 1180 (380); p=.020) mL and rate (827 (327)mL·hr-1 cf 941 (319)mL·hr-1; p=.048) lowered. TTE performance improved (4.6 (1.74) cf 2.4 (1.55) minutes (p=.004). Menthol-spray effects diminished despite repeated applications indicating increased contribution of visceral thermoreceptors to thermal perception. Conclusion Repeated menthol-spray improves exercise capacity but alters thermoregulation potentially conflicting behavioural and thermoregulatory drivers; care should be taken with its use. Carrying and deploying menthol-spray would impose a logistical burden which needs consideration against performance benefit

The effect of hot and cold drinks on thermoregulation, perception and performance: the role of the gut in thermoreception

Purpose. Hot compared to cold drinks alter sweating responses during very low intensity exercise in temperate conditions. The thermoregulatory, perceptual and performance effects of hot compared to cold drinks in hot, dry conditions during high-intensity exercise have not been examined. Method. Ten participants (mean ± SD characteristics age 25 ± 5 years, height 1.81 ± 0.07 m, body mass 73.5 ± 10.6 kg, maximal power output (PMax) 350 ± 41 W). completed two conditions where they drank four boluses (ingested at -9, 15, 30 & 45 minutes respectively) of 3.2 mL.kg-1 (~960 mL total) of either a COLD (5.3°C) or a HOT drink (49.0°C), which were contrasted to a no drink CONTROL. They cycled for 60-minutes (55% PMax in hot (34.4°C) dry (34% RH) ambient conditions followed by a test to exhaustion (TTE; 80% PMax). The thermoregulatory, performance and perceptual implications of drink temperature were measured. Results. TTE was worse in the CONTROL (170 ± 132 s) than the COLD drink (371 ± 272 s; p = .021) and HOT drink conditions (367 ± 301 s; p = .038) which were not different (p = .965). Sweat responses (i.e. reflex changes in mean skin temperature (Tmsk) and galvanic skin conductance) indicated transient reductions in sweating response after COLD drink ingestion. The COLD drink improved thermal comfort beyond the transient changes in sweating. Conclusion. Only COLD drink ingestion changed thermoregulation but improved perceptual response. Accordingly, we conclude a role for gut thermoreception in thermal perception during exercise in hot, dry conditions

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