Toby Mündel

Human thermoregulatory behavior during rest and exercise — A prospective review

Despite the important role of temperature regulation in human behavior, it is frequently overlooked as a thermoregulatory response during both rest and exercise. During rest, the initiation of thermoregulatory behavior is preceded by changes in thermal comfort/sensation, with the temperature of the skin playing a vital signaling role. This behavior maintains heat balance and prevents the activation of autonomic thermoregulatory responses. Recently, self-paced exercise in the heat has been used as a thermo-behavioral model and accordingly, reductions in exercise work-rate in the heat appear sufficient to maintain regulation. Similar to rest, this behavior is mediated by elevations in skin temperature, however the perception of effort appears to be the perceptual trigger.

Drink temperature influences fluid intake and endurance capacity in men during exercise in a hot, dry environment

The effect of different drink temperatures on the perception of exertion and exercise endurance has not been extensively investigated. Consequently, the purpose of the present study was to examine the effect of drink temperature on fluid intake and endurance during cycling in the heat. Eight healthy, non‐acclimated males (26 ± 7 years; maximum oxygen uptake, 54 ± 5 ml kg−1 min−1; mean ±s.d.) cycled to exhaustion at 34°C and at 65% of their peak aerobic power, consuming a drink at either 19°C (CON) or 4°C (COLD). Six of the eight subjects cycled for longer during COLD, with exhaustion occurring at 62 ± 4 min, compared to 55 ± 4 min for CON (P < 0.05; mean ±s.e.m.). Subjects consumed significantly more fluid during COLD compared to CON (1.3 ± 0.3 l h−1 compared to 1.0 ± 0.2 l h−1; P < 0.05). Heart rate tended to be lower by ∼5 beats min−1 during COLD, and rectal temperature during the second half of the exercise period was ∼0.25°C lower during the COLD trial; however, these trends were not significant (P= 0.08 and P= 0.07, respectively). No differences were observed between trials for ventilation, concentrations of prolactin, glucose and lactate or perceived exertion. It is concluded that a drink at 4°C during exercise in the heat enhances fluid consumption and improves endurance by acting as a heat sink, attenuating the rise in body temperature and therefore reducing the effects of heat stress.

Mechanisms of nasal high flow on ventilation during wakefulness and sleep

Nasal high flow (NHF) has been shown to increase expiratory pressure and reduce respiratory rate but the mechanisms involved remain unclear. Ten healthy participants [age, 22 ± 2 yr; body mass index (BMI), 24 ± 2 kg/m(2)] were recruited to determine ventilatory responses to NHF of air at 37°C and fully saturated with water. We conducted a randomized, controlled, cross-over study consisting of four separate ∼60-min visits, each 1 wk apart, to determine the effect of NHF on ventilation during wakefulness (NHF at 0, 15, 30, and 45 liters/min) and sleep (NHF at 0, 15, and 30 liters/min). In addition, a nasal cavity model was used to compare pressure/air-flow relationships of NHF and continuous positive airway pressure (CPAP) throughout simulated breathing. During wakefulness, NHF led to an increase in tidal volume from 0.7 ± 0.1 liter to 0.8 ± 0.2, 1.0 ± 0.2, and 1.3 ± 0.2 liters, and a reduction in respiratory rate (fR) from 16 ± 2 to 13 ± 3, 10 ± 3, and 8 ± 3 breaths/min (baseline to 15, 30, and 45 liters/min NHF, respectively; P < 0.01). In contrast, during sleep, NHF led to a ∼20% fall in minute ventilation due to a decrease in tidal volume and no change in fR. In the nasal cavity model, NHF increased expiratory but decreased inspiratory resistance depending on both the cannula size and the expiratory flow rate. The mechanisms of action for NHF differ from those of CPAP and are sleep/wake-state dependent. NHF may be utilized to increase tidal breathing during wakefulness and to relieve respiratory loads during sleep.

Effect of New Zealand blueberry consumption on recovery from eccentric exercise-induced muscle damage.

BackgroundExercise-induced muscle damage (EIMD) is accompanied by localized oxidative stress / inflammation which, in the short-term at least, is associated with impaired muscular performance. Dietary antioxidants have been shown to reduce excessive oxidative stress; however, their effectiveness in facilitating recovery following EIMD is not clear. Blueberries demonstrate antioxidant and anti-inflammatory properties. In this study we examine the effect of New Zealand blueberries on EIMD after strenuous eccentric exercise.MethodsIn a randomized cross-over design, 10 females consumed a blueberry smoothie or placebo of a similar antioxidant capacity 5 and 10 hours prior to and then immediately, 12 and 36 hours after EIMD induced by 300 strenuous eccentric contractions of the quadriceps. Absolute peak and average peak torque across the knee, during concentric, isometric, and eccentric actions were measured. Blood biomarkers of oxidative stress, antioxidant capacity, and inflammation were assessed at 12, 36 and 60 hours post exercise. Data were analyzed using a two-way ANOVA.ResultsA significant (p < 0.001) decrease in isometric, concentric and eccentric torque was observed 12 hours following exercise in both treatment groups. During the 60 hour recovery period, a significant (p = 0.047) interaction effect was seen for peak isometric tension suggesting a faster rate of recovery in the blueberry intervention group. A similar trend was observed for concentric and eccentric strength. An increase in oxidative stress and inflammatory biomarkers was also observed in both treatment groups following EIMD. Although a faster rate of decrease in oxidative stress was observed in the blueberry group, it was not significant (p < 0.05) until 36 hours post-exercise and interestingly coincided with a gradual increase in plasma antioxidant capacity, whereas biomarkers for inflammation were still elevated after 60 hours recovery.ConclusionsThis study demonstrates that the ingestion of a blueberry smoothie prior to and after EIMD accelerates recovery of muscle peak isometric strength. This effect, although independent of the beverage’s inherent antioxidant capacity, appears to involve an up-regulation of adaptive processes, i.e. endogenous antioxidant processes, activated by the combined actions of the eccentric exercise and blueberry consumption. These findings may benefit the sporting community who should consider dietary interventions that specifically target health and performance adaptation.

The effects of face cooling during hyperthermic exercise in man: evidence for an integrated thermal, neuroendocrine and behavioural response

The present study investigated whether face cooling reduced both the perceived exertion (RPE) and prolactin (PRL) release during hyperthermic exercise. Ten, non‐heat‐acclimated males (23 ± 2 years; maximal oxygen consumption, 56 ± 7 ml kg–1 min–1[mean ±s.d.]) exercised for 40 min on a cycle ergometer at 65% of their peak aerobic power, at an ambient temperature of 33°C (27% relative humidity) with (FC) and without face cooling as a control (CON). With FC, forehead temperature was maintained ∼6°C lower than CON, while other skin sites were similar or slightly warmer in the FC condition. Rectal temperature increased by ∼1.5°C with the same time course in both conditions. A relative bradycardia was observed during FC, with heart rate approximately 5 beats min–1 lower than CON (P < 0.05). Mean plasma lactate was lower during FC (FC, 5.0 ± 0.3 mmol l–1; CON, 5.9 ± 0.3 mmol l–1; P < 0.05) but no differences were observed for plasma glucose, which remained constant during exercise. Levels of PRL were maintained at 175 ± 17 mIU l–1 during exercise for FC, while values for CON increased to a peak of 373 ± 22 mIU l–1 so that towards the end of the exercise, for the same rectal temperature, PRL was significantly lower in the FC condition (P < 0.05). Global and breathing RPE were reduced but only towards the end of the 40 min of exercise during FC, whilst subjective thermal comfort was significantly lower during FC (P < 0.05). We confirm the substantial effect that FC has on the secretion of PRL during hyperthermic exercise but show that it makes a relatively small contribution to the perception of effort when compared to the effect of a cool total skin area as occurs with exercise in a thermoneutral environment.

Acute alcohol consumption aggravates the decline in muscle performance following strenuous eccentric exercise.

This study investigated the effects of acute moderate alcohol intake on muscular performance during recovery from eccentric exercise-induced muscle damage. Eleven healthy males performed 300 maximal eccentric contractions of the quadriceps muscles of one leg on an isokinetic dynamometer. They then consumed a beverage containing 1g/kg bodyweight ethanol (as vodka and orange juice) (ALC). On another occasion they performed an equivalent bout of eccentric exercise on the contralateral leg after which they consumed an isocaloric quantity of orange juice (OJ). Measurement of maximal isokinetic (concentric and eccentric) and isometric torque produced across the knee, plasma creatine kinase (CK) concentrations and muscle soreness were made before and at 36 and 60h following each exercise bout. All measures of muscle performance were significantly reduced at 36 and 60h post-exercise compared to pre-exercise measures (all p<0.05). The greatest decreases in peak strength were observed at 36h with losses of 12%, 28% and 19% occurring for OJ isometric, concentric, and eccentric contractions, respectively. However, peak strength loss was significantly greater in ALC with the same performance measures decreasing by 34%, 40% and 34%, respectively. Post-exercise plasma creatine kinase activity and ratings of muscle soreness were not different between conditions (both p>0.05). These results indicate that consumption of even moderate amounts of alcohol following eccentric-based exercise magnifies the normally observed losses in dynamic and static strength. Therefore, to minimise exercise related losses in muscle function and expedite recovery, participants in sports involving eccentric muscle work should avoid alcohol-containing beverages in the post-event period.

The effects of face cooling on the prolactin response and subjective comfort during moderate passive heating in humans

The purpose of the present study was twofold: first, to determine the extent to which elevated skin temperature is responsible for the hormonal and perceptual responses to passive heating; and second, to determine to what extent face‐cooling can override the effects of raised skin temperature. Sixteen recreationally active, non‐heat‐acclimated volunteers (12 male, 4 female; age, 29 ± 9 years, [mean ±s.d.]) underwent a passive heat exposure for 60 min in a sauna maintained at 58°C (13% relative humidity), conditions under which sweating effectively maintains core temperature. Subjects were allocated to one of two experimental groups which were matched for sex, age, body mass index, body surface area and sweating response; one group received face cooling (FC) every 5 min, whilst the other control group (CON) received none. Mean skin temperatures were elevated by ∼4°C for the 60 min duration (CON, 36.5 ± 0.1°C; FC, 35.7 ± 0.1°C; P < 0.05) but core temperature rose by only ∼0.25°C with no difference between groups. Circulating prolactin remained stable and showed no increase for the FC group, whereas concentrations increased by 102 ± 34% (P < 0.05) for the CON group. No differences were observed between groups for heart rate, but the sensation of heat was less (P < 0.05) with FC. We suggest that a significant component of the prolactin response to moderate passive heating is mediated by facial skin temperature, and selective cooling of the face is associated with improved perception of thermal comfort. These results indicate that the temperature of only a small part of the total skin area (∼10%) has a disproportionately large effect on the hormonal and perceptual responses to heat stress.

Pre-game hydration status, sweat loss, and fluid intake in elite Brazilian young male soccer players during competition

Abstract In this study, we assessed the pre-game hydration status and fluid balance of elite young soccer players competing in a match played in the heat (temperature 31.0 ± 2.0°C, relative humidity 48.0 ± 5.0%) for an official Brazilian soccer competition. Fluid intake was measured during the match, as were urine specific gravity and body mass before and after the game to estimate hydration status. Data were obtained from 15 male players (age 17.0 ± 0.6 years, height 1.78 ± 0.06 m, mass 65.3 ± 3.8 kg); however, data are only analysed for 10 players who completed the full game. The mean (±s) sweat loss of players amounted to 2.24 ± 0.63 L, and mean fluid intake was 1.12 ± 0.39 L. Pre-game urine specific gravity was 1.021 ± 0.004, ranging from 1.010 to 1.025. There was no significant correlation between sweat loss and fluid intake (r = 0.504, P = 0.137) or between urine specific gravity and fluid intake (r = −0.276, P = 0.440). We conclude that young, native tropical soccer players started the match hypohydrated and replaced about 50% of the sweat lost. Thus, effective strategies to improve fluid replacement are needed for players competing in the heat.

Exercise and heat stress: performance, fatigue and exhaustion—a hot topic

Fatigue is suggested to be a general concept that is characterised by an acute impairment in performance and leads to the eventual inability to produce the necessary force, that is, volitional exhaustion.1 Homeostasis is maintained by the physiological regulatory processes occurring throughout the body,2 and during exercise, the development of fatigue and exhaustion is proposed to prevent homeostatic failure.3 Principle to the regulatory systems maintaining homeostasis is that of thermoregulation, and as such the combined stressors of exercise and heat stress are used as a model to investigate the regulatory processes that influence physical performance, the development of fatigue and the onset of exhaustion.4 5 Accordingly, theories have been developed, healthy (lively) debate has arisen and various journals have seen fit to devote special issues—for example, Sports Medicine (vol 37, issues 4–5), Journal of Applied Physiology (vol 104, issue 5) and timely reviews.4,–,7 Within the exercise and heat stress model, two exercise protocols have been used that both describe performance as a dependent variable of time: (1) fixed-intensity (ie, constant workload) exercise—exercise is undergone until volitional exhaustion, and (2) self-paced exercise—which evaluates the time to complete a given task (eg, a set amount of work) where the workload can be adjusted by the exerciser. Both exercise time-to-exhaustion and self-paced exercise performance have been found to be attenuated under heat stress.8,–,16 However, confounding these conclusions is that these exercise protocols evaluate a different combination of physiological processes. Fixed-intensity exercise provides a measure of exhaustion, whereas self-paced exercise provides an indication of the development of fatigue; and arising from this limitation, seemingly opposing theories have developed. Thermoregulation is attained by both passive (ie, non-regulated) and active (ie, regulated) systems.17 During exercise in the heat, passive heat loss …

Effect of transdermal nicotine administration on exercise endurance in men

Nicotine is widely reported to increase alertness, improve co‐ordination and enhance cognitive performance; however, to our knowledge there have been no attempts to replicate these findings in relation to exercise endurance. The purpose of this study was to determine the effects nicotine might have on cycling endurance, perception of exertion and a range of physiological variables. With local ethics committee approval and having obtained informed consent, 12 healthy, non‐smoking men (22 ± 3 years; maximal O2 uptake, 56 ± 6 ml kg−1 min−1, mean ±s.d.) cycled to exhaustion at 18°C and 65% of their peak aerobic power, wearing either a 7 mg transdermal nicotine patch (NIC) or a colour‐matched placebo (PLA) in a randomized cross‐over design; water was available ad libitum. Subjects were exercising at approximately 75% of their maximal O2 uptake with no differences in cadence between trials. Ten out of 12 subjects cycled for longer with NIC administration, and this resulted in a significant 17 ± 7% improvement in performance (P < 0.05). No differences were observed for perceived exertion, heart rate or ventilation. There were no differences in concentrations of plasma glucose, lactate or circulating fatty acids. In the absence of any effect on peripheral markers, we conclude that nicotine prolongs endurance by a central mechanism. Possible modes of action are suggested.