Dissertations / Theses on the topic 'Thermoregulatory responses'

The thermoregulatory responses of subjects wearing two different forms of rugby league jersey, one with plastic sponsorship recognition and numbering (trial Gl) and one without (trial G2), and a lightweight alternative (trial G3), were compared with a trial without any form of upper body garment (trial GO). Ten male volunteers, mean age 20.9 (±2.3) years, height 179.8 (±4.7) cm, weight 80.2 (±8.9) kg, and body surface area 1.99 (±0.13) m2, participated in this study. Subjects had a mean maximal oxygen uptake capacity of 56.0 (±6.3) ml.kg.min-1 and a sum of 8 skinfolds of 80.6 (±23.8) mm. Subjects were exercised at approximately 50% of maximal oxygen uptake in a warm humid environment for 50 minutes. Mean ambient temperature was 27.6°C (±0.32) with a relative humidity of 64.7% (±1.44). Measurements of core and skin (7 sites) temperature, heart rate, oxygen uptake, plasma volume, peak lactate concentration, and pre- and post-trial body weight, hematocrit and garment weight were recorded. The statistical results showed that all subjects experienced significant (p ≤.0001) decreases in body weight representing a percentage decrease ranging from 1.2-1.3%. No significant difference was found between trials with respect to body weight change. No significant effect of garment type was found on pre- and post-trial hematocrit, plasma volume changes or peak blood lactic acid concentration. However, mean peak lactate was highest for trial Gl (5.6 mmol.L-1 ±2.2) and lowest for trial G3 (4.6 mmol.L-1 ±1.27). Post-trial core temperature was significantly (p≤ .0001) higher than the resting value; no significant difference was found between trials. The mean absolute increase for all experimental trials was 0.9°C. A significant (p≤.005) difference between mean total (7 sites) skin temperature was found with a post-hoc test revealing that trials Gl and G2 were significantly higher than trial GO; no significant difference was found when comparing trial G3 with trial GO or when comparing the garments between each other. Mean skin temperature under the garment (4 sites) was found to be significantly (p≤.05) higher for all trials involving a garment when compared with mean skin temperature outside (3 sites) the garment; no significant difference was found between trials. Mean oxygen uptake was significantly different between trials (p≤.005), with trial Gl and G3 found to be significantly lower than trial GO; no difference was found when comparing the garments with each other. Post-trial garment weights were significantly (p≤.001) heavier than pre-trial and were significantly (p≤.0001) different when compared with each other. There was no significant effect on heart rate, haematocrit, plasma volume changes, peak blood lactic acid concentration, or core temperature due to garment type. However, differences in skin temperature suggest that the garment used in trial G3 may have a benefit. Further research should consider the impact of increased exercise intensity and/or environmental temperature and humidity on the measured parameters while wearing the garments described in this study.

The area of thermoregulation during upper body exercise has received limited research in able bodied individuals. The series of studies presented in this thesis investigated the effect of exercise intensity, duration and environmental temperature on thermoregulatory responses, including calf volume and blood flow, during upper body exercise and recovery. In order to manipulate these variables and observe the adaptive thermoregulatory responses, upper body training and heat acclimation were also performed. Chapter 4 examined the effect of exercise intensity (45, 60, 75· and 90% peak power; Wpeak) on thermoregulatory responses during 5 min of upper body exercise. The results of this study suggest a redistribution of blood from the relatively'inactive lower body during arm exercise of intensities up to 60%Wpeak after which point calf volume did not 'I significantly decrease further. The calf volume decrease is possibly a result of vasoconstriction reducing blood pooling in the leg. Chapter 5 examined the effects of exercise duration (15,30, arid 45 min at 60%Wpeak) on thermoregulatory responses during and after upper body exercise. During upper body exercise at 60% Wpeak calf volume decreased up to 15 min with no further decrease thereafter. In all trials calf blood flow was greater at the cessation of exercise compared to rest suggesting hyperaemia occurred at the end of exercise. Chapter ~ examined the effects of exercise (30 min, 60%Wpeak) in different environmental temperatures (21, 27 ~nd 33°C) on thermoregulatory responses. Calf skin blood flow from Laser Doppler measurements increased in all trials with a concomitant decrease in calf volume. The decrease in the calf volume..reported therefore reflected a greater and more substantial muscle vasoconstriction compared to increased skin blood flow. There was a greater decrease in calf volume during the 27°C trial which appears to be, a result of a lower skin blood flow response compared to exercising in 33°C. Chapter 7 examined the effect of 8 weeks of upper body training on thermoregulatory responses during upper body exercise. Upper body training reduced aural temperature and heat storage at a given power output as a result of increased whole body sweating and heat flow. Upper body training produced a smaller calf volume change after training at the same absolute exercise intensity demonstrating less leg vasoconstriction which was possibly as a result of a reduced response to sympathetic nervous activity or the fact that exercise was performed overall at a lower intensity post training (47% vs. 60%Wpeak). Chapter 8 examined the effect cSf exercising (30 min, 60%Wpeak) evrpry day in the h~at for 7 . '. days on'thermoregulatory responses to upper body exercise in the heat. There was reduced core temperature during exercise. The calf volume decrease was significantly greater during exercise in the heat following heat acclimation which may be a .result of increased vasoconstriction compensating, for an increase in skin blood flow to reduce venous pooling and therefore to maintain both stroke volume and blood flow to the skin. The lower body appears to have an important role in both cardiovascular stability as well as thermoregulation during upper body exercise.. It is proposed that this is achieved by reducing venous pooling in the calf thus increasing the availability of blood for maintaining stroke volume and increasing skin blood flow during exercise. The responses at the calf during exercise can be adapted through heat acclimation and upper body training.

Following on from Rio de Janeiro 2016, the Tokyo 2020 Paralympic Games will present a unique challenge for athletes, needing to prepare and adapt to the potential challenging environmental conditions of 20-27°C and ~73% relative humidity. It is well known that during exercise in hot and/or humid climates, able-bodied athletes experience an increase in thermal strain and a reduction in performance compared to cooler/drier conditions. Yet these conditions prove even more problematic for athletes, who as a consequence of their impairment have a dysfunctional thermoregulatory system, such as athletes with a spinal cord injury (SCI). To date, the thermoregulatory responses of athletes with an SCI have been an under-studied area of research. To gain a greater understanding of how heat balance is altered in individuals with an SCI and the thermoregulatory consequences as a result, studies need to first be conducted at rest, removing the additional metabolic heat production from exercise. Although a large majority of athletes with an SCI compete indoors in wheelchair court sports (e.g. wheelchair basketball and rugby), exercising even in these climate-controlled environments has been shown to place these athletes under considerable thermal strain. In light of this, it is remarkable that existing research on the thermoregulatory responses of athletes with an SCI during exercise is scarce, especially studies encompassing real-world sporting environments. Athletes with high level lesions (tetraplegia, TP) are a particularly under-studied population group shown to have a greater thermoregulatory impairment than individuals with low level lesions (paraplegia, PA) during continuous exercise. Thus the aim of this thesis was to investigate the thermoregulatory responses of athletes with an SCI at rest and during real-world sporting scenarios, with specific focus on athletes with TP. Study 1 aimed to determine how evaporative heat loss is altered, as a result of an SCI, compared to the able-bodied (AB), and the effect lesion level has on this response. The results provide evidence that in individuals with TP, even at rest, evaporative heat loss is not large enough to balance the heat load, when evaporation is the primary source of heat dissipation. Even though in individuals with PA Tgi increased by a smaller magnitude and they possessed a greater sweating capacity than individuals with TP, at ambient temperatures above Tsk latent heat loss is insufficient to attain heat balance, compared to the AB. To investigate the thermoregulatory responses of athletes with an SCI during real-world sporting scenarios Study 2 examined athletes with TP compared to athletes with PA during 60 min of intermittent sprint wheelchair exercise on a wheelchair ergometer. The study was conducted in conditions representative of an indoor playing environment for wheelchair rugby and basketball (~21°C, 40% relative humidity). Results demonstrated that, despite similar external work, athletes with TP were under greater thermal strain than athletes with PA. Study 3 s novel approach investigated both physiological responses and activity profiles of wheelchair rugby players during competitive match play. Despite players with TP covering 17% less distance and pushing on average 10% slower, they were under a greater amount of thermal strain than players with non-spinal related physical impairments (NON-SCI). Furthermore, this study demonstrated that players with TP that had a larger body mass, larger lean mass, covered a greater relative distance and/or were a higher point player had a greater end Tgi. These data provide an insight for coaches and support staff regarding which players may need greater attention in regards to cooling strategies or breaks in play. The effectiveness of cooling practices currently employed by athletes with TP has not been previously investigated. Study 4 determined the effectiveness of pre-cooling, using an ice vest alone and in combination with water sprays between quarters, at attenuating thermal strain in athletes with TP. Using the activity profile data from Study 3, an intermittent sprint protocol, conducted on a wheelchair ergometer, was used to represent a wheelchair rugby match. The combination of cooling methods lowered Tgi and Tsk to a greater extent than pre-cooling only, despite neither cooling condition having a positive or negative effect on performance. Unexpectedly, the pre-cooling only condition lowered Tgi, compared to no cooling, throughout the subsequent exercise protocol, even though the reduction in Tsk was not long lasting. This thesis provides comprehensive evidence that athletes with TP experience heightened thermal strain during both rest and real-world sporting scenarios compared to the AB, athletes with PA, and within the sport of wheelchair rugby. Athletes with TP should employ practices, such as appropriate cooling methods or alter playing tactics to reduce thermal strain and the likelihood of attaining a heat related injury.

Currently no previous study has isolated the independent influence of body fat (BF) on thermoregulatory responses from the confounding biophysical factors of body mass and metabolic heat production (Hprod). Therefore, seven lean (L, BF:10.7 ± 4.1%) and seven non-lean (NL, BF:32.2 ± 6.4%) males matched for total body mass (TBM, L: 87.8 ± 8.5 kg, NL: 89.4 ± 7.8 kg; P= 0.73), cycled for 60 min in a 28.2 ±0.2˚C and 27 ± 10% RH room at i) a Hprod of 546 W; and ii) a Hprod of 7.5 W·kg lean body mass (LBM). Rectal (Tre) and esophageal (Tes) temperatures, and local sweat rate (LSR) were measured continuously; while whole body sweat loss (WBSL) was measured from 0-60 mins. At 546 W, changes in Tre (L: 0.74 ± 0.16ºC, NL: 0.83 ± 0.14ºC), mean local sweat rate (MLSR) based on an average of upper-back and forearm local sweat rates (L: 0.65 ± 0.25, NL: 0.59±0.12 mgcm-2min-1) and WBSL (L: 568 ± 28 mL, NL: 567 ± 29 mL) were similar (P>0.58). At 7.5 W·kg LBM, the L group had greater changes in Tre (L: 0.87 ± 0.16ºC, NL: 0.55 ± 0.11ºC), MLSR (L: 0.83 ±0 .38, NL: 0.41 ± 0.13 mgcm-2min-1) and WBSL (L: 638 ± 19 mL, NL: 399 ± 17 mL) (P<0.05). In conclusion, i) body fat does not independently alter thermoregulatory responses during exercise; ii) core temperature comparisons between groups differing in BF should be performed using a Hprod normalized for TBM, not LBM.

Many physiological variables exhibit circadian rhythmicity. The circadian rhythm in core temperature is a well-established and it has been extensively studied during both passive and exercise heat exposure. In females, a circamensal rhythm in core temperature is also present and well established. However, there is little knowledge about whether there is an interaction effect between time of day and phase of menstrual cycle on core temperature and thermoregulatory and cardiovascular responses during and following exercise. The studies in the present thesis were designed to investigate such an interaction effect on the effector responses of the thermoregulation and cardiovascular systems during the exercise and post-exercise periods. The first experiment was designed to examine the time of day effect on thermoregulatory and cardiovascular responses during and following exercise in female subjects. Eight healthy participants completed 30-min exercise at 65%Y02peak at 07:00 and 19:00hr. Core temperature was significantly higher by 0.3, 0.4 and 0.3DC at rest (P=O.OOI), during the exercise (P=O.OOI) and post-exercise (P=0.008) periods in the evening compared to the morning. The second experiment was designed to examine the phases of menstrual cycle on thermoregulatory and cardiovascular responses during and following exercise. Ten healthy participants completed two exercise protocols (65%Y02peak) during the late follicular and luteal phases of the menstrual cycle (day 10-12 and day 20-22 after the onset of menstruation, respectively). Core temperature tended to be higher in the luteal phase compared with the late follicular phase (0.2DC) both at rest (p=O.064) and during exercise (p=0.062), whereas the heat-loss mechanisms were unaffected by menstrual cycle phase. In addition, resting stroke volume and cardiac output was greater in the late follicular phase compared to the luteal phase. The third experiment was designed to explore the interaction effect between time of day and phase of the menstrual cycle on thermoregulatory and cardiovascular responses during the exercise and the post-exercise periods. Ten healthy participants completed four exercise protocol (65% Y02peak); two exercise protocols in the morning of the late follicular and luteal phases, and two exercise protocols in the evening of the late follicular and luteal phases. Core temperature was higher in the evening of both phases of the menstrual cycle during exercise (p=O.OOI) and the post-exercise periods (p=O.003). There was an interaction effect between times of day and phase of the menstrual cycle on mean skin temperature during the exercise (p=0.048) and the post-exercise periods (p=0.006), a lower mean skin temperature in the evening compared with the morning during the late follicular phase and higher in the evening than in the morning in the luteal phase. However, there was no interaction of times of day and phase of menstrual cycle for other thermoregulatory and cardiovascular parameters measured. The results in the thesis indicate that temperature regulation is set around higher values in the evening and late luteal phase of the cycle, but that these changes are likely independent of each other. Future work, should more systematically investigate these responses, collecting data at more times of day and phases of the cycle.

The accumulated stresses of training and competition may temporarily cause impairments in an athlete’s physiological and muscular function, leading to suboptimal performance levels. Cold-water immersion (CWI) has become a widely used post-exercise recovery method to accelerate the recovery process by purportedly reducing the symptoms associated with exercise-induced muscle damage (EIMD). However, the underlying physiological mechanisms, which mediate the effects of CWI, are not well understood. Therefore, the aim of this thesis was to investigate the influence of cold-water immersion (CWI) on limb blood flow and thermoregulatory responses following different modes of exercise. In study 1 (Chapter 4), the reliability of Doppler ultrasound in the assessment of superficial femoral artery blood flow (FABF) was examined under resting conditions. A Doppler ultrasound scan of the superficial femoral artery was measured on eight recreationally active male participants; twice on the same day separated by 5-min (within-day), and on a separate day (between-days). The coefficient of variation (CV) for mean blood flow (MBF) was ~16 % and ~20 % for within and between-days, respectively. A relatively small standard error of measurement (SEM) was found both within day, 13.30 mL·min-1 (95% CI, -14.79 to 38.40 mL·min-1) and between-day, 17.75 mL·min-1 (95% CI, -40.12 to 30.88 mL·min-1) for MBF differences. These findings suggest duplex Doppler ultrasound is a reliable method to collect measurements of FABF under resting conditions. The purpose of study 2 and 3 was to determine the influence of different degrees of water immersion cooling on FABF and cutaneous blood flow (CBF) and thermoregulatory responses after endurance (Chapter 5) and resistance (Chapter 6) exercise, respectively. Participants completed a prescribed endurance of resistance exercise protocol prior to immersion into 8 ºC (cold) or 22 ºC (cool) water to the iliac crest or rested non-immersion (CON) in a randomized order. Limb blood flow and thermoregulatory responses were measured before and up to 30-min after immersion. In both studies, thigh skin temperature (Tskthigh) (P < 0.001) and muscle temperature (Tmuscle) (P < 0.01) were lowest in the 8 ºC trial compared with 22 ºC and control trials. However, femoral artery conductance (FVC) was similar after immersion in both cooling conditions and was reduced (~50-55 %) compared with the CON condition 30-min after immersion (P < 0.01). Similarly, there was a greater thigh (P < 0.01) and calf (P < 0.05) cutaneous vasoconstriction during and after immersion in both cooling conditions relative to CON with no differences noted between 8 and 22 ºC immersion. Together, these findings suggest that colder water temperatures may be more effective in the treatment of EIMD and injury after both endurance and resistance exercise, respectively, due to greater reductions in Tmuscle and not limb blood flow per se. The aim of study 4 (Chapter 7) was to compare the influence of CWI and whole body cryotherapy (WBC) on FABF and CBF and thermoregulatory responses after endurance exercise. On separate days, participants completed a continuous cycle ergometer protocol before being immersed semi-reclined into 8 ºC water to the iliac crest for 10 min (CWI), or exposed to 2.5 min (30 s -60 ºC, 2 min -110 ºC) WBC in a specialized cryotherapy chamber, in a randomized order. Limb blood flow and thermoregulatory responses were measured before and up to 40-min after immersion Reductions in Tskthigh (P < 0.001) and Tmuscle (P < 0.001) were larger in CWI during recovery. Similarly, decreases in FVC were greater (~45-50 %) in the CWI condition throughout the recovery period (P < 0.05). There was also a greater skin vasoconstriction observed in CWI at the thigh (P < 0.001) and calf (P < 0.001) throughout the post-cooling recovery period. These results demonstrate that CWI may be a better recovery strategy compared with WBC due greater reductions in both Tmuscle and limb blood flow. This thesis provides a novel insight into the influence of different degrees of water immersion cooling, as well as WBC, on limb blood flow and thermoregulatory responses after different modes of exercise. These findings provide practical application for athletes and an important insight into the possible mechanisms responsible for CWI in alleviating inflammation in sport and athletic contexts.

The independent influence of maximum oxygen consumption (VO2max) and running economy (RE) on thermoregulatory responses during treadmill exercise have not been isolated due to the complex interactions between VO2max, RE, body mass, body surface area (BSA), and metabolic heat production (Hprod). The purpose of the thesis is to determine whether large differences in VO2max and/or running economy independently alter thermoregulatory responses during running in a neutral environment. Seven aerobically unfit (LO-FIT: ~ 40 mlO2·kg-1·min-1) and sevn aerobically fit (HI-FIT: ~ 60 mlO2·kg-1·min-1) males, matched for body mass and BSA ran at 1) a fixed metabolic heat production of 640 W (FHP trial) and 2) 60%VO2max (REL trial). Also, seven high RE (HI-ECO: ~ 185 mlO2·kg-1·km-1) and seven low RE (LO-ECO: ~ 220 mlO2·kg-1·km-1) males, matched for body mass, BSA and VO2max (~ 60 mlO2·kg-1·min-1) ran at a 1) fixed Hprod of 640 W (FHP trial) and 2) fixed running speed of 10.5 km·h-1 (FRS trial). All trials were performed in a thermoneutral environment. The data was analyzed using a two-way mixed ANOVA, with the significance level set at an alpha of 0.05 for all comparisons. It was hypothesized that thermoregulatory responses (i.e., core temperature and sweating), during exercise will not be independently altered by VO2max, but will be altered by any differences in heat production and running economy. The FHP trial resulted in similar changes in esophageal temperature (∆Tes), changes in rectal temperature (∆Tre), and WBSL between the HI-FIT and LO-FIT groups, despite vastly different %VO2max. Whereas the REL trial resulted in greater ΔTeso, ΔTre, and WBSL in the HI-FIT group, in parallel with their greater Hprod. In groups greatly differing in RE, the FHP trial elicited similar ∆Tes, ∆Tre, and WBSL; however the HI-ECO group had to run faster to achieve the same heat production as their LO-ECO counterparts. Moreover, a FRS of 10.5 kmh-1 produced a greater Hprod, ∆Tes, ∆Tre, and WBSL in the LO-ECO group. In conclusion, thermoregulatory responses are determined by Hprod and RE, not VO2max, when differences in mass and BSA are eliminated between groups. Thus, these findings support the initially stated hypotheses.

This experimental project determined the effect of glycerol hyperhydration in 4 trained male triathletes on endurance performance and cardiovascular and thermoregulatory responses. For this purpose, the subjects received, using a randomized, double-blind and crossover protocol, either a glycerol (1.2 g glycerol/kg/bodyweight (BW) with 18 ml/kg/BW of aspartame-flavored juice plus 8 ml/kg/BW of distilled water) or a placebo solution (aspartame-flavored juice and water only) over an 80 min period, 40 min before exercise, then performed 2 h of cycling at 65% of maximal oxygen consumption (VO[subscript 2] max), which was immediately followed by an endurance performance test to exhaustion. All trials were conducted at 25[degrees Celsius], 38-42% relative humidity (RH). During exercise, subjects consumed a 6% sports drink (SD) solution at a rate of 166 ml every 20 min, up to min 100. Preliminary results suggest that glycerol hyperhydration could attenuate dehydration better than water hyperhydration during a cycling exercise at 65% VO[subscript 2] max in a thermoneutral climate, which could improve core temperature, but not HR. With respect to the endurance performance test, the comparison of the mean of each group reveals that glycerol hyperhydration did not increase time to exhaustion."--Résumé abrégé par UMI.

The mechanisms which account for the diminished responsiveness (tolerance) of an individual to a drug, as a result of prior exposure to that drug, are not yet fully understood. Recently, it has been suggested that drug tolerance is a learned adaptive response. This possibility was examined by studying the effect of ethanol on body temperature and behavioral thermoregulatory responses of Sprague-Dawley rats. Two major studies were conducted. The first study examined the initial dose-related effects of ethanol (1, 2, or 3 g/kg i.p.); the second study examined the effect of ethanol (2.5 g/kg i.p.) administered on 14 consecutive days. Rats were tested in a thermocline, a hollo plexiglass tube in which a linear temperature gradient (6-36°C) was established through local heating and cooling of opposite ends of the tube. The position of rats in the thermocline was detected by a series of infrared light emitting diodes and photocells. The body temperature of rats in the thermocline was transmitted by a temperature sensitive telemetry capsule surgically placed in the peritoneal cavity. Validation studies demonstrated that rats reliably responded to temperature cues within the thermocline. In the first experiment ethanol produced a dose-related decrease in body temperature. All rats following injection initially selected an ambient temperature cooler than baseline. Rats receiving control treatment or the high dose of ethanol eventually shifted to a warmer ambient temperature. Activity levels were depressed equally by all three doses of ethanol. In the second experiment tolerance developed to the hypothermic effect of ethanol. A diminished response to ethanol was evident by the second test day and was maximal by day 7. Ethanol treated rats selected a cooler ambient temperature than control rats throughout the 14 day period, and activity levels continued to be depressed by ethanol throughout the 14 days. On the fifteenth day all rats were given an injection of saline. Rats which had previously received daily ethanol injections exhibited a hyperthermic response to saline compared to control rats. These results suggest that ethanol altered the central control of thermoregulation by lowering and possibly broadening the thermoregulatory set point. There was evidence for a conditioned hyperthermic response, but not a learned behavioral response, which contributed to the tolerance development.

Athletes have continually sought to improve their physical performance. In order to accomplish this, athletes experiment with performance enhancing drugs, which are readily available to the athlete today. Cocaine, being one of them, is traditionally and popularly believed to increase muscular endurance and possess anti-fatiguing properties. The scientific literature as to whether cocaine is truly a performance enhancing drug is inconclusive. Moreover, few if any studies have been conducted on exercise performance following long term, repeated cocaine administration. The purpose of the present study was to determine the effects of 35 days of cocaine administration (25 mg/kg/day) on maximal endurance exercise capacity. Data were collected from six untrained male Sprague-Dawley rats. Resting and exercise heart rate and body temperature were recorded via radio telemetery. Running time to exhaustion was recorded via one weekly maximal treadmill exercise bout to exhaustion (26 m/min, at a 10% grade). Compared to saline controls, cocaine significantly decreased run time to exhaustion, following acute and chronic administration. Cocaine administration also significantly decreased maximal exercise heart rate. Chronic cocaine had minimal effects on resting heart rate and resting and exercise body temperature during maximal exercise conditions. These data indicate that daily, chronic cocaine administration significantly reduces endurance exercise capacity, and suggests that the decreased physical work capacity following cocaine is related to a decreased ability of the heart to function under maximal exercise conditions.

The existence of a patent foramen ovale (PFO) has been known about for nearly 2,000 years. The prevalence of a PFO has been shown to be 25-40% in the general population. Despite the fact that blood flowing through a PFO acts as a shunt, there has been little research looking at the effect a PFO has on physiology in otherwise healthy humans. In Chapter IV, the effect of a PFO on core temperature (Tcore) prior to, and during exercise, was investigated. The design of this experiment included appropriate controls for a thermoregulatory study (i.e. measuring at same time of day, appropriate hydration and food intake, etc.). Results from this study indicate that subjects with a PFO (PFO+) have a Tcore that is ~0.4°C higher at rest and during exercise than subjects without a PFO (PFO–). Additionally, this study showed that PFO– subjects do not increase Tcore to the same extent breathing cold air as they do breathing ambient air during a 10-minute exercise bout, whereas there was no difference in Tcore increase between these two conditions for PFO+ subjects. These findings suggest that the difference in Tcore between PFO+ and PFO– subjects is potentially due to differences in respiratory heat loss. The studies for Chapter V examined differences in thermoregulatory and ventilatory responses during hot water (40°C) and cold water (20°C) immersion. This study found that compared to PFO– subjects, PFO+ subjects 1) increase Tcore at the same rate during hot water immersion and 2) do not cool off as quickly during cold water immersion. Additionally, in subjects who reached a ventilatory threshold, PFO+ subjects had blunted ventilatory responses to increased Tcore compared to PFO– subjects. Finally, in Chapter VI it was shown that PFO+ subjects have blunted ventilatory responses during acute exposure to hyperoxic and normoxic hypercapnia. However, there were no differences in ventilatory responses between PFO+ and PFO– subjects during exposure to either isocapnic or poikilocapnic hypoxia. These findings suggest that PFO+ subjects have a blunted central chemoreflex. This dissertation contains previously, unpublished co-authored material.

This study sought to determine the independent influence of hypoxia on thermoregulatory responses to exercise in compensable and uncompensable hot conditions. Eight participants completed three experimental trials of cycling in either normoxia (21% O2) or hypoxia (13% O2) in order to manipulate relative exercise intensity (%VO2peak), since VO2peak was reduced by ~30% in hypoxia. When trials were matched for %VO2peak, changes in core temperature and local sweat rates (LSR) were significantly lower in the hypoxic trial as a result of a lower rate of metabolic heat production (Hprod) in order to maintain a similar %VO2peak compared to normoxia. However, when Hprod was fixed between normoxic and hypoxic trials the systematic differences in core temperature and LSR were eliminated. Conversely, at a fixed Hprod skin blood flow (SkBF) was greater in hypoxia compared to normoxia by ~40%. Despite improvements in SkBF, the potential for maximum heat loss was unaffected during an incremental humidity ramp protocol, resulting in no difference between normoxia and hypoxia in the critical ambient vapour pressures at which core temperature inflected upwards. These data further demonstrate, using a within-subjects design, that metabolic heat production, irrespective of large differences in %VO2peak, determines thermoregulatory responses during exercise. Furthermore, this study suggests that the influence of large differences in skin blood flow on heat dissipation may be lesser than previously thought.

The use of solutions containing creatine and glycerol (Cr/Gly) has become popular amongst athletes as a means of hyperhydrating prior to exercise in the heat, since achieving an optimal hydration status appears to be a critical factor for temperature and cardiovascular regulation during exercise in the heat. Hyperhydration has previously been achieved by means of a pre-exercise water loading strategy with the use of hydrating agents (i.e., Cr and Gly) in combination. Certain problems are related to this hyperhydration strategy and are investigated in this thesis. Firstly, the use of Gly has been prohibited and added to the WADA banned list due to the potential of Gly plasma expansion properties, to mask the use of doping substances such as erythropoietin stimulants. However, the scientific basis of the inclusion of Gly as a “masking agent” remains inconclusive. Secondly, the addition of high CHO amounts to the Cr/Gly strategy is central to successful Cr uptake and subsequent hyperhydration. Thirdly, high CHO intake has been linked to high plasma TAG in the athletic population and partial replacement of CHO with insulinotropic agents, such as alpha lipoic acid (Ala), a natural antioxidant and co-factor in the pyruvate dehydrogenase complex, has been shown to enhance Cr uptake under conditions of reduced CHO. On a separate note, Cr and Ala have been found to individually improve Glu tolerance and lipid markers in sedentary individuals while the combined effects of Cr/Ala supplementation on Glu tolerance and lipid markers of sedentary individuals have not been investigated. The aim of chapter 3 was to determine the effects of a hyperhydrating supplement containing 1.0 g/kg of BM of Gly, 10.0 g of Cr and 75.0 g of Gluon on doping-relevant blood parameters. This hyperhydration did not significantly alter PV or any of the doping-relevant blood parameters (e.g., Hct, [Hb], Ret (%) and tHb-mass). Due to the fact that most athletes, in situations where they may be subject to testing by WADA, may choose rapid hyperhydration protocols, the effects of a shorter supplementation 2 protocol on doping related blood parameters, was investigated in chapter 3. For this purpose, a separate cohort of participants consumed the Gly/Cr/Glu supplement over the course of one day. Despite a significant increase in BM over the course of supplementation lasting 8 hours, PV changes and the blood-relevant doping markers of interest were not significantly affected, even when urinary [Gly] was clearly above the urinary [Gly] observed following typical dietary Gly intake. In conclusion, this study showed that supplementation with a hyperhydrating solution containing Gly for 7 days or a short supplementation protocol lasting one day did not significantly alter doping- relevant blood parameters. The aim of chapter 4 was to determine whether Cr/Gly-induced thermoregulatory and cardiovascular responses are maintained when part of the Glu in the Cr/Gly supplement is replaced with the insulintropic agent Ala. Median and range values of TBW increased significantly by 2.1 (1.3-3.3) L and 1.8 (0.2-4.6) L in the Cr/Gly/Glu and Cr/Gly/Glu/Ala groups, respectively (P=0.03). During constant load exercise, HR and Tcore were significantly lower post-supplementation: HR was reduced on average by 3.3±2.1 beats/min and by 4.8±3.3 beats/minute (mean±S.D.) and Tcore by 0.2±0.1 (mean±S.D.) in the Cr/Gly/Glu and Cr/Gly/Glu/Ala groups, respectively. The reduction in HR and Tcore was not significantly different between the supplementation groups. In comparison to the established hyperhydrating Cr/Gly/Glu supplement, a supplement containing Cr/Gly/Ala and decreased amount of Glu provides equal improvements in thermoregulatory and cardiovascular responses during exercise in the heat. The aim of chapter 5 was to determine whether acutely increasing dietary CHO intake prior to endurance events, through the intake of hyperhydrating Cr/Gly solution enriched with Glu, leads to changes in plasma lipids of endurance trained cyclists and whether replacing part of the Glu within this supplement with an insulin potentiating agent, such as Ala, attenuates these changes. Fasting concentration of TAG increased significantly 3 (P<0.01) after supplementation with Cr/Gly/Glu (Pre, 0.9±0.2 mmol/L; Post, 1.3±0.4 mmol/L) and Cr/Gly/Glu/Ala (Pre, 0.8±0.2 mmol/L; Post 1.2±0.5 mmol/L) but the increase in plasma TAG concentration was not significantly different between the two groups. Supplementation had no effect on fasting concentration of total-, HDL-, and LDL- cholesterol and insulin resistance. The acute increase in dietary CHO intake during the 7 days of supplementation with Cr/Gly/Glu induces an increase in plasma TAG concentration that is not attenuated by partial replacement of CHO with Ala. The aim of chapter 6 was to determine whether Cr supplementation, in the absence of exercise would lead to improvements in Glu tolerance in healthy overweight sedentary males and if Cr supplementation combined with Ala, would improve Glu tolerance and plasma lipids in healthy overweight sedentary males. The purpose of this pilot study was to determine the efficacy of Cr and Cr/Ala combined supplementations in improving Glu tolerance, insulin sensitivity and lipid profile of healthy overweight sedentary males. A four-week supplementation with Cr improved Glu tolerance while supplementation with Cr/Ala failed to have such an effect. Nevertheless, supplementation with Cr/Ala for 4 weeks decreased LDL-cholesterol significantly. None of the other blood markers were significantly different following 4 weeks of supplementation with Cr or Cr/Ala. This study found that Cr improved Glu tolerance without any changes in insulin sensitivity or lipid profile of healthy overweight sedentary males, in the absence of exercise. Moreover, the addition of Ala to Cr, had no added effect on Glu uptake, insulin sensitivity or plasma lipids apart from LDL-cholesterol. However, a randomised control trial with a higher sample size, recruiting both experimental, and control groups should be carried out to confirm these findings.

Three studies were performed to examine biophysical sources of individual variability in the thermoregulatory responses to exercise, and the influence of skin blood flow on heat loss potential during severe heat stress. Study 1 investigated whether unbiased comparisons of changes in rectal temperature (ΔTre) should be compared at a fixed absolute rate of heat production (Hprod; W) or a fixed Hprod per unit mass (W/kg), and whether local sweat rates (LSR) should be compared at a fixed evaporative requirement for heat balance (Ereq; W) or a fixed Ereq per unit of surface area (W/m2), between independent groups of unequal body mass and body surface area (BSA). Study 2 examined whether individual variation in ΔTre, whole-body sweat loss (WBSL), and steady-state LSR is best explained by biophysical factors related to Hprod, Ereq, and body size, and if factors related to aerobic fitness (VO2max) and body fatness correlate with the residual variance in these responses. Study 3 tested whether alterations in skin blood flow shift the critical vapour pressure (Pcrit) above which core temperature could no longer be regulated in hot/humid conditions, indicating altered heat loss potential from the skin. In study 1, exercise at fixed absolute Hprod and Ereq resulted in greater ΔTre and LSR in smaller individuals (smaller mass and BSA), but exercise at set Hprod in W/kg and Ereq in W/m2 resulted in no differences in ΔTre and LSR, respectively, regardless of body size and %VO2max. In study 2, 50-71% of the individual variation in ΔTre, whole-body sweat loss (WBSL), and steady-state LSR was explained by Hprod (W/kg), absolute Ereq (W) and Ereq (W/m2) respectively, while body fat percentage and %VO2max contributed merely 1-4% to the total variability. In study 3, despite a ~20% lower skin blood flow, Pcrit was unaffected by a large reduction in skin blood flow following iso-smotic dehydration, with no differences in core and skin temperatures and sweating observed. Collectively, these findings suggest that between-group comparisons and modelling of thermoregulatory responses must first consider biophysical factors related to metabolic heat production and body size, rather than factors related to VO2max and body fatness. Furthermore, lower levels of skin blood flow may not impair maximum heat dissipation from the skin to the external environment during severe passive heat stress as previously thought.

The rise in body temperature following the completion of preliminary "warm-up" protocols, may have detrimental effects on the performance of endurance based events under environmental temperatures of 18-24°C. The aim of this thesis was to determine the influence of pre-warming on different modes of prolonged exercise under ambient temperatures of 20°C. Two pre-warming protocols were devised which would promote the desired elevation in body temperature prior to exercise. These protocols were then subsequently used to determine the influence of pre-exercise elevations in body temperature on the metabolic and thermoregulatory responses to prolonged submaximal, intermittent and soccer-specific intermittent exercise performance under ambient temperatures of 20°C.

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy Johannesburg, 2018.
Future climate change scenarios predict that many arid and semi-arid ecosystems within southern Africa, will get warmer and drier with increased frequency of droughts. Although the effects of climate change may only be apparent over a few decades, understanding the physiological and behavioural flexibility of individuals currently inhabiting hot and dry climates provides an analogue for conditions likely to become prevalent in the future. To enhance our understanding of how a species may respond to future hotter and drier environments, I set out to investigate seasonal variation in behaviour and thermoregulation of two ungulate species with differing water dependency in a semi-arid savanna. I focused on thermoregulatory (body temperature) and behavioural responses (activity and microclimate selection) of the water-dependent blue wildebeest (Connochaetes taurinus), and the arid-adapted gemsbok (Oryx gazella gazella) free-living in the Kalahari. Both species prioritised behavioural thermoregulation in the form of cool microclimate selection during the heat of the day and reduced both diurnal and 24 h activity, particularly when conditions were hot and dry. Both species experienced high maximum 24 h body temperature when conditions were hot and low minimum 24 h body temperatures when conditions were dry, resulting in a large amplitude of 24 h body temperature rhythm during the hot dry period. Yet, wildebeest appeared to be more sensitive to changes in aridity with a larger amplitude of 24 h body temperature rhythm compared to gemsbok (3.1 ± 0.2 °C vs. 2.1 ± 0.5 °C), during the drought. These seasonal analyses imply that the species behavioural and thermoregulatory responses were influenced by seasonal changes in water and forage availability. Low minimum 24 h body temperatures may result from an energy deficit during the dry season, but no study to date has explicitly linked changes in body temperature of free-living ungulates, to forage quality within the environment. I therefore investigated the influence of vegetation greenness on body temperature and activity of blue wildebeest and gemsbok inhabiting the same environment. I then investigated if the responses of gemsbok were heightened in a more arid environment. I used Normalized Difference Vegetation Index (NDVI) as a standardized index of vegetation greenness, which can be considered a proxy for vegetation productivity and quality. Both species reduced total 24 h activity and became hypothermic when exposed to brown vegetation but when exposed to brown vegetation minimum 24 h body temperatures were lower for blue wildebeest compared to gemsbok. When exposed to more extreme aridity, gemsbok showed an exaggerated lowering of minimum 24 h body temperatures. Under conditions of low food availability, the cost of thermoregulation may become too demanding. Therefore, when food resources are limited in quality, wildebeest and gemsbok in arid regions appear to prioritize the conservation of energy over the maintenance of a high body temperature. Within seasonal environments, access to water is often the limiting factor for plants and animals. I therefore investigated how distance to water (i.e., how frequently animals were likely to have accessed drinking water) during the hot season influenced microclimate selection, activity and body temperature of blue wildebeest and gemsbok. Both species selected similarly cool microclimates during the heat of the day, with slight enhancement in the quality of microclimates selected when they were further from water. Both species decreased activity during the heat of the day when they were further from water. Gemsbok were able to compensate for their reduced activity during the heat of the day and showed little change in total 24 h activity, but wildebeest showed a more exaggerated decline in activity during the heat of the day for which they were unable to compensate, i.e. total 24h activity of wildebeest declines when they were further away from water sources. Both species displayed higher maximum 24 h body temperatures when they were further away from water, with the hyperthermia being exaggerated for the wildebeest compared to gemsbok. Hyperthermia in both species resolved following the first rains and likely access to drinking water. Access to water appears to be the primary driver towards hyperthermia in the wildebeest, potentially resulting from dehydration during thermal stress. In summary, I have investigated behavioural and thermoregulatory flexibility that large African ungulates currently inhabiting hot and dry climates currently employ. I have shown that ungulates in the Kalahari may differ in their use of microclimate selection and activity patterns to buffer thermal, energetic and water stressors. My study is unique in that I have looked at where the animal was in space and time and linked it to their physiological and behavioural responses. I have, therefore, quantified microclimate selection, activity and body temperature responses in relation to NDVI and distance to water and have shown that the driving mechanisms behind the seasonal changes of body temperature and activity patterns is access to energy and water. I have further enhanced our existing knowledge and created the link between body temperature, vegetation quality and distance to surface water for antelope of the Kalahari and effectively assessed a functional trait. With climate change predicted to increase ambient temperatures and have less predictable rainfall in the semi-arid Kalahari, wildebeest will be forced to remain within the Kalahari, because historical migratory paths have been blocked by fences, and they may not have the behavioural and physiological flexibility to survive a hotter and drier future.
LG2018

These studies investigated the impact of intensity and body temperature on performance and cardiovascular regulation during high intensity and prolonged exercise. In study 1, polyphenol antioxidant supplementation proved to have no effect on exercise performance and related variables (gross efficiency, perceived exertion, maximal power) during exercise in the heat. Furthermore, there were no differences between the cardiovascular or thermoregulatory responses between control and antioxidant treatments. Study 2 utilized an integrative approach to investigate a classic topic in exercise physiology, namely, is the cardiac output to oxygen consumption relationship linear across a wide range of exercise intensities? The slope of the CO vs. VO2 relationship was significantly reduced from 70 to 100% of VO2max when compared to the slope from 40 to 70% of VO2max (2.0 ± 0.4 vs. 4.4 ± 0.3 l/min, p = 0.025). This finding, in combination with the plateau and eventual reduction in stroke volume at high intensity exercise compared to moderate intensity exercise (146.0 ± 16.6 vs. 138.5 ± 14.9 ml/beat, p = 0.015), argues in favor of a cardiac limitation to high intensity exercise. This study also showed that the pattern of oxygen extraction at the whole body level (arterial venous O2 difference) and the muscle level (deoxygenated hemoglobin) is not similar and that muscle specific differences exist regarding oxygen extraction. Study 3 determined that hyperthermia (elevation of skin temperature by 4.3°C and core temperature by 0.8°C) did not reduce SV independent of the increase in HR. Even under conditions of moderate hyperthermia the reduction in SV is due to the increase in HR and temporally unrelated to increases in cutaneous blood flow. In summary, antioxidant supplementation had no effect on performance, cardiovascular, or thermoregulatory responses to exercise in the heat in well trained subjects. High intensity exercise is associated with a reduced rate of increase in the CO vs. VO2 relationship. Finally, hyperthermia does not reduce SV during exercise when HR is maintained at normal levels.
text

碩士
中國醫藥學院
中國藥學研究所
88
Puerarin is an isoflavone compound isolated from Pueraria lobata. The Puerariae radix has been used for antipyretic in Chinese. Puerarin, a beta-adrenergic receptor blocker, possesses anticonvulsive, antiarrhythmic and antihypertension effects. It also reduces 2,4-dinitrophenol-induced hyperthermia. However, the effects of puerarin on normal body temperature and pyrogenic fever are unknown. On this account, in the present study, experiments were carried out to assess the effects of puerarin on thermoregulatory responses in unanesthetized rats. Puerarin (100mg/10ml,i.c.v.;5-30mg/kg, i.p.) caused a dose-related fall in both colonic temperature and the 5-HT release in the hypothalamus at room temperature. The serotonin release in the hypothalamus was monitored with a microdialyzed probe is association with microdialysis-high perforemance liquid chromatography. Puerarin induced hypothermia was attenuated by pretreatment with 5,7-dihydroxytryptamine (5,7-DHT; a serotonin neurotoxin, 200mg/10ml; i.c.v., one week ago), or (-)-pindolol (a 5-HTIA receptor/b adrenoceptor antagonist; 0.05, 0.5mg/kg; s.c.) but potentiated by (±)-8-hydroxydiopropylamino-teralin (8-OH-DPAT; a 5-HT1A receptor agonist; 0.05mg/kg; s.c.). In addition, the puerarin induced hypothermia was attenuated by (±)-2,5-dimethoxy-4-iodoamphetamine (DOI; 5-HT2 receptor agonist; 5, 10mg/10ml; i.c.v.; 0.5, 1mg/kg; i.p.) or quipazine (a 5-HT2 receptor agonist; 0.5, 1mg/kg; i.p.), but potentiated by ketanserin (5-HT2 receptor antagonist; 1mg/kg; i.p.) or pirenperone (5-HT2 receptor antagonist; 0.2mg/kg; s.c.). These results indicate that puerarin may act through 5-HT1A receptor activation or 5-HT2 receptor antagonism within the brain to induce its hypothermia. The fever induced by either lipopolysaccharide (LPS, 100mg/kg; i.p.) or interleukin-1b (IL-1b, 10ng/10ml; i.c.v.) was attenuated by treatment with puerarin (100mg/10ml, i.c.v.; 10, 30mg/kg, i.p.). Our microdialysis data revealed that puerarin (10, 30mg/kg; i.p.) reduces the increased 5-HT release in the hypothalamus and fever provoked by IL-1b injection. The hyperthermia induced by either S-nitroso-N-acetylpenicillamine (nitric oxide donor, 10mg/10ml; i.c.v.), sodium nitroprusside (NO releaser, 20mg/10ml; i.c.v.), 8-Bromo-cGMP (cGMP analogue, 100mg/10ml; i.c.v.), PGE2 (100mg/10ml; i.c.v.), or 8-Bromo-cAMP (cAMP analogue, 40mg/10ml; i.h.) was attenuated by treatment with puerarin (10, 30mg/kg; i.p.) in rats. In conclusion, puerarin exerts its thermoregulatory response mainly through the serotoninergic, nitrergic or prostaglandinergic pathways in the central nervous system of rat brain.