The problem of “optimum” acclimatisation

Summary A study was carried out on three groups of 20 male subjects to determine the combination of environmental stress and a standard rate of work of 5 kcal/min that will give the optimum level of acclimatisation.Each group was acclimatised at one of three temperature conditions (wet-bulb temperatures of 32.2 °, 33.9 ° and 35.6 ° C) and thereafter tested also under the remaining two conditions.The degree of acclimatisation was judged by the physiological reactions to a standard work rate of 5 kcal/min at the various wet-bulb temperatures. The test at a wet-bulb temperature of 32.2 C revealed that °optimum acclimatisation was obtained when men were acclimatised at 33.9 °C W.B. The test at 33.9 °C W.B. illustrated that the physiological reactions of the group acclimatised at 35.6 ° C W.B. were decidedly poor when compared to those of the groups acclimatised at 32.2 ° and 33.9 ° C W.B. The test carried out at 35.6 ° C W.B. showed that, irrespective of the wet-bulb temperature at which the men were acclimatised, their heat tolerance to the test environment was poor.     

Development of thermoregulation in the kitten

In normal kittens thermoregulation developed over the first 45 days of age. This maturational sequence went from a mean rectal temperature (T_B) of 37.0°C at 5 days of age to adult levels (38.2 ± 0.2°C) at about 7 weeks of age. Up until about 14 days of age the predominant response to being removed from the nesting box and placed at an ambient temperature of 23 to 25°C was a decrease in T_B of about 0.02°C/min. In response to stronger thermal challenges (i.e., short periods at + 60°C or ? 15°C) all kittens showed, from the first day of life, the ability to detect and move along a thermal gradient as reflected in an approach to warmth and an avoidance of cool. At ?15°C the kittens showed a decrease in T_B of about 0.2°C/min at 10 days decreasing to about 0.1°C/min at 40 days of age. After 45 days of age shivering as well as piloerection appeared immediately with cold onset and for short periods (i.e. less than 2 hours) at this temperature combined behavioral and physiological regulation sufficed to maintain the temperature at approximately 37.5°C. In response to heating the kittens showed a mean T_B increase of about +0.05°C/min at 10 days decreasing to +0.02°C/min at 45 days of age, at which time panting was also fully developed. These data demonstrate that the development of normal thermoregulation in the cat follows a time course of up to seven weeks.     

Cortisol as a sensitive index of heat-intolerance

The relationship between plasma cortisol levels, core temperatures, heat storage and the appearance of subjective manifestations of heat intolerance were investigated in two groups of 4 and 3 men, respectively. The first group underwent 4 randomized experimental sessions: a control session and three heat-exposure sessions (A: 48°C, 34 Torr, 80 min; B: 55°, 15 Torr, 120 min; C: 48°C, 15 Torr, 180 min). During control periods, the subjects were maintained in a thermoneutral climate (28°C, 10.5 Torr). The second group of subjects was studied before and after five successive daily exposures to hot and humid conditions (D: 43°C, 32 Torr, 165 min). Signs of subjective discomfort in experiments A and B were accompanied by an increase in cortisol values over control day values, and this increase began at a mean rectal temperature of about 38°C. Condition C was well tolerated, the plasma cortisol remained at basal levels and mean rectal temperature averaged 38°C at the end of the exposure. Repeated exposures in condition D improved heat tolerance with a lesser effect on plasma cortisol levels and a lower body temperature at the end of exposure. Circulating cortisol is shown to be a very sensitive index of heat stress heralding the onset of poor tolerance of severe climates. The relation between concomitant levels of cortisol and rectal temperatures, in fit men, is affected by additional factors (hypotension, uncomfortable posture). These reduce tolerance time and are not reflected by body temperatures, but by rapidly increasing cortisol levels.     

The effects of different levels of water deficit on physiological responses during heat stress

Summary The influence of different levels of water deficit on the physiological responses to heat stress of two well-acclimatised subjects was studied. The subjects worked continuously at a rate of 2,000 ft.lb/min for four hours at 32.2 ° C W. B., 33.9 ° C D.B. and an air velocity of 0.25–0.4 m/sec. Man, even when in water deficit, operates most efficiently when he replaces all the fluids lost in sweat and urine by drinking water in small amounts at frequent intervals. When a specific level of water deficit is maintained throughout the 4 hours of heat exposure body temperature, heart rate, and sweat rate reach equilibrium at values which are significantly different from those recorded under conditions of complete water balance; the more severe the level of dehydration the higher the body temperatures and heart rates, and the lower the sweat rates. No indication of any failure of the temperature regulating mechanisms or fatigue of the sweat glands was found and a possible explanation for this difference with previously reported results is provided.     

Effect of posture on body temperature of young men in cold air

We studied eight young adult men to see whether a supine posture caused a fall in body core temperature in the cold, as it does in thermoneutral conditions. In air at 31°C (thermoneutral), a supine posture for 3 h reduced mean aural, gastric, oesophageal and rectal temperatures by 0.2–0.4°C, compared to upright and increased femoral artery blood flow from 278 (SEM 42) ml · min⁻¹ whilst upright to 437 (SEM 42) ml·min⁻¹ whilst supine. In cold air (8°C) the supine posture failed to reduce these temperature differences significantly, or to increase femoral blood flow; it reduced heart rate, and increased arterial systolic and pulse pressures adjusted to carotid sinus level, less than in thermoneutral conditions. However, the behaviour of core temperature at the four sites was significantly nonuniform between the two postures in the cold, mainly because the supine posture tended to reduce rectal temperature. It may have done so by reducing heat production in the muscles of the pelvis, since it reduced overall metabolic rate from 105 (SEM 8) to 87 (SEM 4) W · m⁻² in the cold. In other respects the results indicated that posture ceased to have an important effect on body core temperatures during cold stress.     

Safe cooling limits from exercise-induced hyperthermia

We evaluated the cooling rate of hyperthermic subjects, as measured by three estimates of deep core temperatures (esophageal, rectal and aural canal temperatures), during immersion in a range of water temperatures. The objective of the study was to compare the three indices of core temperature and define safe cooling limits when using rectal temperature to avoid the development of hypothermia. On 4 separate days, seven subjects (four males, three females) exercised for 45.4±4.1 min at 65% at an ambient temperature of 39°C, RH: 36.5%, until rectal temperature (T _re) increased to 40.0°C (39.5°C for two subjects). Following exercise, the subjects were immersed in a circulated water bath controlled at 2, 8, 14 and 20°C until T _re returned to 37.5°C. When T _re reached normothermia during the cooling period (37.5±0.05°C), both esophageal (T _es) (35.6±1.3°C) and aural canal (T _ac) (35.9±0.9°C) temperatures were approaching or reaching hypothermia, particularly during immersion in 2°C water (T _es=34.5±1.2°C). On the basis of the heat loss data, the heat gained during the exercise was fully eliminated after 5.4±1.5, 7.9±2.9, 10.4±3.8 and 13.1±2.8 min of immersion in 2, 8, 14 and 20°C water, respectively, with the coldest water showing a significantly faster cooling rate. During the immersion in 2°C water, a decrease of only 1.5°C in T _re resulted in the elimination of 100% of the heat gained during exercise without causing hypothermia. This study would therefore support cooling the core temperature of hyperthermic subjects to a rectal temperature between 37.8°C (during immersion in water >10°C) and 38.6°C (during immersion in water <10°C) to eliminate the heat gained during exercise without causing hypothermia.     

Rapid, selective procedure for isolation of spontaneous temperature-sensitive mutants of Moloney leukemia virus

A procedure for selection of spontaneous mutants of Moloney murine leukemia virus (Mol-MuLV) was devised based on the following observations. At the permissive temperature (32°C), S+L? cells infected with wt Mol-MuLV became rounded up and readily detached from the dish. At the nonpermissive temperature (39°C), S+L? cells infected with wt virus became rounded up while those that were uninfected, or infected with temperature-sensitive (ts) mutants, remained fully attached. In the selection procedure rounded cells were removed and discarded from Mol-MuLV-infected S+L? cultures after 3 days' incubation at 39°C and virus stocks were harvested from those cultures after further incubation for 3 days at 32°C.Virus harvested from infected S+L? cells subjected to the procedure for selection of ts mutants had ratios of viral titers at 32°C:39°C = 3 when the multiplicity of infection was 0.02–0.1. One subsequent cycle of selection resulted in increasing the ratio further to 7- to 8-fold but further cycles were ineffective in increasing the ratio. Of 100 clones picked from one enriched stock of nonmutagenized Mol-MuLV, 29 had a ratio 32°C:39°C ≧ 5 whereas no such putative mutants were found among 42 clones picked from a stock of Mol-MuLV that had not been put through the selection procedure. Several ts mutants were purified by repeated cloning and some characteristics are described.The work described above employed a new assay for murine leukemia viruses. It was based on the use of XC-cells to identify the proportion of a population of mouse cells infected in suspension with Mol-MuLV. The titer of a stock of wild-type (wt) virus was quantitatively the same whether the assay was carried out at 32°C or at 39°C.     

Gross efficiency of muscular work during step exercise at -15°C and 21 °C

In an effort to assess the effect of ambient temperature on the gross efficiency (Eff_g) of step exercise 12 subjects performed a modified step test either at —15 °C or 21°C ascending to three different heights (corresponding to light, moderate and heavy work), for 20 min each with a frequency of 18 steps min^-1. Heart rate (HR), rectal temperature, skin temperatures and heat flux from skin were continuously measured. Oxygen consumption was measured during the last 5 min of each step height and perceptions of thermal sensation were recorded. The results indicate that, while using conventional clothing adequate in these temperatures, Eff_g is altered in a contradictory manner. At —15°C Eff_g increased with increasing work load, whereas at 21°C it decreased when the work load increased. The highest Eff_g (heavy work at —15°C and light work at 21°C) values are reflected as rather similar rectal temperatures (37.4–37.7°C) and identical mean skin temperatures (32.8 °C) as well as the same (slightly warm) thermal sensation of the legs. At — 15 °C the lowest Eff_g in light work was probably hue to the need to warm up the muscles. At 21°C, on the contrary, the activation of heat dissipation systems was probably responsible for the lowest Eff_g in heavy work.     

Physiological responses and manual performance in humans following repeated exposure to severe cold at night

We evaluated human physiological responses and the performance of manual tasks during exposure to severe cold (–25°C) at night (0300–0500 hours) and in the afternoon (1500–1700 hours). Thirteen male students wearing standard cold protective clothing occupied a severely cold room (–25°C) for 20 min, and were then transferred to a cool room (10°C) for 20 min. This pattern of exposure was repeated three times, for a total time of exposure to extreme cold of 60 min. The experiments were started either at 1500 hours or 0300 hours and measurements of rectal temperature, skin temperature, blood pressure, performance in a counting task, hand tremor, and subjective responses were made in each condition. At the end of the experiment at night the mean decrease in rectal temperature [0.68 (SEM 0.04)°C] was significantly greater than that at the end of the experiment in the afternoon [0.55 (SEM 0.08)°C, P<0.01]. After the second cold exposure at night the mean increase in diastolic blood pressure [90 (SEM 2.0) mmHg] was significantly greater than that at the end of the second cold exposure in the afternoon [82 (SEM 2.8) mmHg, P<0.01]. At the end of the second cold exposure at night, mean finger skin temperature [11.8 (SEM 0.8)°C] was significantly higher than that at the comparable time in the afternoon [9.0 (SEM 0.7)°C, P<0.01]. Similarly for the toe, mean skin temperature at the start of the second cold exposure at night [25.6 (SEM 1.5)°C] was significantly higher than in the afternoon [20.1 (SEM 0.8)°C, P<0.01]. The increased skin temperatures in the periphery resulted in increased heat loss. Since peripheral skin temperatures were highest at night, the subjects noted diminished sensations of thermal cold and pain at that time. Manual dexterity at the end of the first cold exposure at night [mean 83.7 (SEM 3.6) times·min^–1] had decreased significantly more than at the end of the first cold exposure in the afternoon [mean 89.4 (SEM 3.5) times·min^–1, P<0.01]. These findings of a lowered rectal temperature and diminished manual dexterity suggest that there is an increased risk of both hypothermia and accidents for those who work at night. Electronic Publication     

Subcutaneous interstitial pressure in man and dogs exposed to heat and exercise stress

Summary Interstitial fluid pressure (IFP) was measured by the wick method in six young men. During exercise in the heat, IFP progressively decreased, and this decrease was maintained after cessation of exercise. In two men working in the same conditions after heat acclimatisation IFP became initially positive before steadily declining. In three anaesthetised dogs exposed to heat IFP also declined, but in a thermoneutral environment it rose towards atmospheric pressure. It is suggested that IFP could be used as a measure of filtration forces operating across the capillary wall. Fluid dynamics in the interstitial space of heat acclimatised man differed, however, from that of unacclimatised man and heat exposed dogs. It is postulated that these changes may be related to movement of protein from the interstitial to the plasma compartments during exercise after acclimatisation.     

Heat reactions of Bushmen

When Bantu males are exposed to ambient air temperatures of 78, 82, 86 and 90 °F Effective Temperature it is possible to distinguish clearly between unacclimatised, partially acclimatised and highly acclimatised states. A sample of Bushmen was exposed to this range of E. T.'s in a portable climatic chamber. Their rectal temperatures at the end of the third hour of exposure reached 101 °F at 78 ° and 82 °F E.T., 102.2 °F at 86 °F E.T. and 102.5 °F at 90 °F E.T. Sweat rates were highest in the first hour of exposure in all four heat stress conditions. Sweat rates decreased generally throughout the three-hour period, but the rank order of sweat rates were maintained. Sweat rates were plotted against rectal temperatures for each hour and also for the average values of the three hours of exposure. Curves fitted to the Bushmen data lie between the curves fitted to the data of unacclimatised and acclimatised Bantu for each of the three hours. When curves relating the mean sweat rates for the three hours of exposure at each of the E.T. conditions are compared with those for unacclimatised and acclimatised Bantu, it is found that the curve drawn on the Bushmen data again occupy a position midway between the other two curves. These three groups and a group of U. S. students are also compared in this paper in terms of physiological limits based on a steady level of rectal temperature, and based on the percentages of the samples exceeding a rectal temperature of 101 °F and 102.5 °F. The limiting E.T.'s for the Bushmen were found to be similar to those of unacclimatised Bantu and, generally, higher than for the U. S. students.     

Human physiological responses to immersion into water of different temperatures

To differentiate between the effect of cold and hydrostatic pressure on hormone and cardiovascular functions of man, a group of young men was examined during 1-h head-out immersions in water of different temperatures (32°C, 20°C and 14°C). Immersion in water at 32°C did not change rectal temperature and metabolic rate, but lowered heart rate (by 15%) and systolic and diastolic blood pressures (by 11%, or 12%, respectively), compared to controls at ambient air temperature. Plasma renin activity, plasma cortisol and aldosterone concentrations were also lowered (by 46%, 34%, and 17%, respectively), while diuresis was increased by 107%. Immersion at 20°C induced a similar decrease in plasma renin activity, heart rate and systolic and diastolic blood pressures as immersion at thermoneutrality, in spite of lowered rectal temperature and an increased metabolic rate by 93%. Plasma cortisol concentrations tended to decrease, while plasma aldosterone concentration was unchanged. Diuresis was increased by 89%. No significant differences in changes in diuresis, plasma renin activity and aldosterone concentration compared to subjects immersed to 32°C were observed. Cold water immersion (14°C) lowered rectal temperature and increased metabolic rate (by 350%), heart rate and systolic and diastolic blood pressure (by 5%, 7%, and 8%, respectively). Plasma noradrenaline and dopamine concentrations were increased by 530% and by 250% respectively, while diuresis increased by 163% (more than at 32°C). Plasma aldosterone concentrations increased by 23%. Plasma renin activity was reduced as during immersion in water at the highest temperature. Cortisol concentrations tended to decrease. Plasma adrenaline concentrations remained unchanged. Changes in plasma renin activity were not related to changes in aldosterone concentrations. Immersion in water of different temperatures did not increase blood concentrations of cortisol. There was no correlation between changes in rectal temperature and changes in hormone production. Our data supported the hypothesis that physiological changes induced by water immersion are mediated by humoral control mechanisms, while responses induced by cold are mainly due to increased activity of the sympathetic nervous system. Accepted: 4 February 1999     

Thermoregulatory responses to cold during a 7-week acclimatisation process in rabbits

A group of six rabbits reared at +20°C ambient temperature was adapted to moderate cold by housing for seven weeks at +10°C. Rectal and skin temperatures, metabolic heat production and respiratory evaporative heat loss were recorded continuously over 1 h for each animal on 3 days per week in the climatic chamber.There was no significant change either of rectal or of ear skin temperature during the acclimatisation process. On the other hand, metabolic heat production was progressively reduced (20% in the 7th week). Slight changes of mean skin temperature and respiratory evaporative heat loss could not account for compensation. Therefore it must be concluded that both adaptive improvement of peripheral insulation and reduction of heat production were achieved during the acclimatisation process. Both processes together ensure that deviations of core temperature are minimal. The possible origin of the functional adaptive effects is discussed. The results are in full agreement both with former neurophysiological results and with system-theoretical considerations of adaptive processes.Dedicated to the 60th birthday of Professor Dr. Kurt Brück     

Human temperature regulation when given the opportunity to behave

This study aimed to test the primary hypotheses that human thermoregulatory behavior is: (1) initiated before changes in rectal or esophageal temperatures; and (2) accompanied by indiscernible differences in sweating or shivering. This was achieved by placing nine, healthy, males in a situation where they were free to move between a cold (~8 °C) and a hot (~46 °C) environment. Upon behaving [i.e., move from cold to hot (C→H) or from hot to cold (H→C)], skin, rectal, and esophageal temperatures, indices of cutaneous vasomotor tone, metabolism and evaporation, and local and whole-body thermal discomfort were recorded. Rectal temperatures were similar at H→C (37.1 ± 0.2 °C) and C→H (37.1 ± 0.2 °C); yet esophageal temperatures were higher at C→H (36.9 ± 0.2 vs. 36.8 ± 0.2 °C). Skin temperature (C→H, 28.4 ± 0.9 vs. H→C, 35.0 ± 0.6 °C) and vasomotor tone were drastically different upon the decision to behave. Metabolic heat production was lower at H→C (79 ± 10 W/m²) than at C→H (101 ± 20 W/m²), yet there were no statistical differences in evaporative heat loss (C→H, 23 ± 33 W/m² vs. H→C, 52 ± 36 W/m²). Whole-body thermal discomfort was similar at C→H and H→C, yet there were inter-segmental differences. These findings indicate that skin temperature, not core temperature, plays a signaling role in the decision to behaviorally thermoregulate. However, this behavior does not occur in the complete absence of autonomic thermoregulatory responses.     

The fate of herpes simplex virus type 2 DNA during abortive infection at 42°C of human embryonic lung cells

It has been reported previously that when human embryonic lung cells were infected with herpes simplex virus type 2 and shifted to 42°C, a small fraction of cells survived 8 days incubation at 42°C while no uninfected cells could survive this incubation period. In the present work, incorporation of thymidine into viral and cellular DNA was investigated at 37 and 42°C, and also after subsequent shift of the temperature back to 37°C, by means of density gradient analysis. If infected cells are incubated at 42°C up to 6 days and subsequently shifted down to 37°C, viral DNA and virus particles are synthesized. However, following 8 days at 42°C, no viral DNA is synthesized after shift down, even though the presence of viral antigens could be demonstrated.     

Thermoregulatory responses of firemen to exercise in the heat

Summary Twelve volunteer (VF) and 12 professional firemen (PF) wearing only brief trunks exercised on an electrically-braked cycle ergometer at three-five exercise intensities. After 45 min of exercise at 75 W, the exercise intensity was elevated in steps of 25 W every 15 min until the subject was exhausted. Air temperature was regulated to equal skin temperature (36°–38°C) and relative humidity was regulated at 52%. The two groups of firemen were comparable in terms of body mass, age and maximum oxygen consumption. Their oxygen consumption, rectal and skin temperatures, sweating and heart rate were measured during the tests. Blood lactate concentration was measured before, during and after the test. The physiological strain was higher in VF as indicated by higher heat storage, heart rate, skin and rectal temperatures. Sweat rate tended to be lower in VF than PF. The results indicated a better adaptation of the professional compared to the volunteer firemen to work in the heat, although the degree of heat acclimatization was considered to be equally minimal in both groups.     

Effect of submaximal exercise at low temperatures on pulmonary function in healthy young men

Summary In order to understand more fully the effect on pulmonary function of whole body exposure to cold during submaximal exercise, we measured pulmonary function indices in ten healthy male students and ten healthy male forestry workers of similar age following submaximal treadmill walking at different temperatures in a climatic chamber. After measuring the maximal aerobic capacity with a cycle ergometer test, the subjects had to walk on four separate occasions in the climatic chamber at an intensity of 70%–75% of their individual maximal heart rate; the first at normal room temperature and then randomly, either at 0°C or at −20°C, and vice versa. The duration of each walk was 8 min. Finally, each subject had to walk in the chamber at −20° C for 17 min. Flow volume spirometry was performed at room temperature 1, 5, 10, and 20 min after exercise and the values were compared to baseline values taken prior to the last walking test. There were only minor changes in pulmonary function indices following exercise at different temperatures. Only one student showed a reduction of over 15% in peak expiratory flow rate after an 8-min walk at −20° C. It seems that submaximal exercise of short duration, even at a temperature as low as −20° C, does not impair pulmonary function in healthy young men.     

Body temperature and its effect on leukocyte mobilization, cytokines and markers of neutrophil activation during and after exercise

We investigated the influence of rectal temperature on the immune system during and after exercise. Ten well-trained male cyclists completed exercise trials (90 min cycling at 60% time trial) on three separate occasions: once in 18°C and twice in 32°C. Twenty minutes after the trials in 32°C, the cyclists sat for ∼20 min in cold water (14°C) on one occasion, whereas on another occasion they sat at room temperature. Rectal temperature increased significantly during cycling in both conditions, and was significantly higher after cycling in 32°C than in 18°C (P < 0.05). Leukocyte counts increased significantly during cycling but did not differ between the conditions. The concentrations of serum interleukin (IL)-6, IL-8 and IL-10, plasma catecholamines, granulocyte-colony stimulating factor, myeloperoxidase and calprotectin increased significantly following cycling in both conditions. The concentrations of serum IL-8 (25%), IL-10 (120%), IL-1 receptor antagonist (70%), tumour necrosis factor-α (17%), plasma myeloperoxidase (26%) and norepinephrine (130%) were significantly higher after cycling in 32°C than in 18°C. During recovery from exercise in 32°C, rectal temperature was significantly lower in response to sitting in cold water than at room temperature. However, immune changes during 90 min of recovery did not differ significantly between sitting in cold water and at room temperature. The greater rise in rectal temperature during exercise in 32°C increased the concentrations of serum IL-8, IL-10, IL-1ra, TNF-α and plasma myeloperoxidase, whereas the greater decline in rectal temperature during cold water immersion after exercise did not affect immune responses.     

Prediction of the thermoregulatory response for clothed immersion in cold water

Summary A multi-compartmental thermoregulatory model was applied to data of ten resting clothed males immersed for 3 h in water at 10 and 15°C. Clothing consisted of a dry suit and either a light or heavy undergarment, representing a total insulation of 0.15 (0.95) or 0.20 m²°CW⁻¹ (1.28 clo), respectively. Data were grouped according to low (<14%) and high (14 to 24%) body fat individuals. Mean decreases in rectal temperature ranged from 0.79 to 1.38°C, mean decreases in the mean weighted skin temperature ranged from 6.3 to 10.2°C, and mean increases in the metabolic rate ranged from 33.9 to 80.8 W. The model consists of eight segments, each representing a specific region of the body. Each segment is comprised of compartments representing the core, muscle, fat, skin, and clothing. Each compartment is assigned thermophysical values of heat conduction and heat capacitance, and with the exception of clothing, physiological values of blood flow and metabolic heat production. During cold exposure, responses are directed towards increased heat production in the form of shivering and heat conservation in the form of vasoconstriction and convective heat exchange at the vascular level. Agreement between the model predictions and the experimental observations was obtained by adjusting the parameters governing these responses. These adjusted parameters were 1) the onset of limb shivering with an exponential half-time of 30 min, 2) the fractional value of 0.5 for the convective heat exchange between the core compartments of the limbs and the blood flowing through these compartments, 3) the fractional contribution of trunk shivering to overall shivering, which ranged from 0.77 to 0.95, and 4) the onset of vasoconstriction with exponential half-times that ranged from 3 to 25 min. Steady state was predicted to occur within 4 h and a heat balance analysis indicated that the limbs were responsible for most of the body's heat loss while acquiring most of their own heat from the trunk through convective heat exchange with the central blood.     

Post-exercise cooling techniques in hot,humid conditions

Major sporting events are often held in hot and humid environmental conditions. Cooling techniques have been used to reduce the risk of heat illness following exercise. This study compared the efficacy of five cooling techniques, hand immersion (HI), whole body fanning (WBF), an air cooled garment (ACG), a liquid cooled garment (LCG) and a phase change garment (PCG), against a natural cooling control condition (CON) over two periods between and following exercise bouts in 31°C, 70%RH air. Nine males [age 22 (3) years; height 1.80 (0.04) m; mass 69.80 (7.10) kg] exercised on a treadmill at a maximal sustainable work intensity until rectal temperature (T _re) reached 38.5°C following which they underwent a resting recovery (0–15 min; COOL 1). They then recommenced exercise until T _re again reached 38.5°C and then undertook 30 min of cooling with (0–15 min; COOL 2A), and without face fanning (15–30 min; COOL 2B). Based on mean body temperature changes (COOL 1), WBF was most effective in extracting heat: CON 99 W; WBF: 235 W; PCG: 141 W; HI: 162 W; ACG: 101 W; LCG: 49 W) as a consequence of evaporating more sweat. Therefore, WBF represents a cheap and practical means of post-exercise cooling in hot, humid conditions in a sporting setting.