The effect of water temperature on the hormonal response to prolonged swimming

Implications of Heat Stress-induced Metabolic Alterations for Endurance Training

Inducing a heat-acclimated phenotype via repeated heat stress improves exercise capacity and reduces athletes̓ risk of hyperthermia and heat illness. Given the increased number of international sporting events hosted in countries with warmer climates, heat acclimation strategies are increasingly popular among endurance athletes to optimize performance in hot environments. At the tissue level, completing endurance exercise under heat stress may augment endurance training adaptation, including mitochondrial and cardiovascular remodeling due to increased perturbations to cellular homeostasis as a consequence of metabolic and cardiovascular load, and this may improve endurance training adaptation and subsequent performance. This review provides an up-to-date overview of the metabolic impact of heat stress during endurance exercise, including proposed underlying mechanisms of altered substrate utilization. Against this metabolic backdrop, the current literature highlighting the role of heat stress in augmenting training adaptation and subsequent endurance performance will be presented with practical implications and opportunities for future research.

Behaviour of salivary testosterone and cortisol in men during an Ironman Triathlon

Endurance exercise induces notable acute hormonal responses on the gonadal and adrenal hormones. The purpose of this study was to assess the changes in salivary testosterone (Ts), salivary cortisol (Cs) and T/C ratio during long-distance triathlon. Ten well-trained male triathletes participated in the study and were assessed for hormonal changes at four time-points (pre-competition, post-swimming, post-cycling, and post-running phases). Ts decreased from pre-competition to post-swimming (from 93.37 pg/mL to 57.63 pg/mL; p < .01) and increased during two other parts of the competition to almost pre-competition values (cycling: 79.20 pg/mL, p = .02; running: 89,66 pg/mL, p = .04, respectively). Cs showed a similar behaviour; decreasing in the post-swimming phase (1.74 pg/mL) and increasing in the other transitions (post-cycling: 7.30 pg/mL; post-running: 13.31 pg/mL), with significant differences between pre-competition and post- competition values (p = .01). Conversely, T/C increased significantly from pre-competition to post-swimming phase (p = .04) to later decrease until the end of the competition. Overall, T/C significantly decreased (p < .05). In conclusion, during an Ironman triathlon, hormone values fluctuate in response to the demands of the competition. Ts and Cs decrease after-swimming, increase after-cycling and reach the maximum values after-running. T/C reflects overall catabolic status.

Acute increase in arterial stiffness after swimming in cooler water

Cold stimuli increase arterial stiffness, but it has not been explored whether arterial stiffness increases after swimming in cooler water. To investigate the effects of water temperature on changes in arterial stiffness after swimming, 13 men participated in three trials of 20-min swimming in 25 and 30°C water (S25 and S30, respectively) and sitting at poolside (CON) in random order. There were no significant differences between the S25 and S30 trials in mean swimming distance (719 vs. 722 m) and heart rate reserve during swimming (63% vs. 63%). Sublingual temperature was lower after swimming in 25°C water versus before swimming. Aortic pulse wave velocity (aortic PWV, an index of central arterial stiffness based on applanation tonometry) and brachial-ankle pulse wave velocity (baPWV, an index of systemic arterial stiffness based on air plethysmography) were higher 30 min after versus before swimming in 25°C water. Aortic PWV recovered to pre-swimming levels by 60 min after swimming in 25°C water, but baPWV was higher even at 60 min after swimming. PWVs did not change in the CON and S30 trials. Systemic vascular resistance based on Doppler ultrasonography did not change, but forearm vascular resistance based on strain-gauge plethysmography was higher 30 and 60 min after swimming in 25°C water. Heart rate was higher, but stroke volume was lower 30 min after swimming in 25°C water, resulting in no detectable change in cardiac output. In conclusion, arterial stiffness increases acutely after moderate-intensity swimming in cooler water.

Tumor necrosis factor-α, TNF receptor, and soluble TNF receptor responses to aerobic exercise in the heat

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Aerobic exercise in the heat promotes modest increases in plasma TNF-α and STNFR1.

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Increases in TNF-α and STNFR1 are likely driven by changes in core temperature.

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TNFR1 and 2 expression on non-classical monocytes is blunted one hour post-exercise.

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TNFR1 expression on non-classical monocytes is elevated during exercise in the heat.

The purpose of this study was to evaluate the effects of aerobic exercise in the heat on circulating concentrations of tumor necrosis factor (TNF)-α, soluble TNF receptors (STNFR1&2), and surface expression of TNFR1&2 on monocyte subpopulations. Twelve recreationally active Caucasian men (24.4 ± 3.4 yrs.; 180.0 ± 6.8 cm; 81.5 ± 8.0 kg; 47.2 ± 4.8 mL·kg⁻¹·min⁻¹) completed an exercise protocol in three environmental conditions: high temperature/low humidity [HTLH; 35 °C, 20% relative humidity (RH)]; high temperature/moderate humidity (HTMH; 35 °C, 45%RH); and moderate temperature/moderate humidity (MTMH; 22 °C, 45%RH). Each protocol consisted of a 60-minute cycling trial at 60% VO₂max, a 15-minute rest, and a time-to-exhaustion trial at 90% VO₂max (TTE). Blood was sampled before (PRE), immediately after (POST) the 60-minute trial, immediately post-TTE (PTTE), and one-hour post-TTE (REC). Circulating TNF-α and STNFR1&2 were assayed. TNFR1&2 expression on monocyte subsets was measured by flow cytometry on a subset of participants (n = 8). TNF-α area under the curve with respect to increase (AUCi) was greater during HTMH compared to MTMH and HTLH. STNFR1 concentration was greater during HTMH compared to MTMH. With all trials combined, STNFR1 concentration increased from PRE to POST, PTTE, and REC. TNFR1 expression on non-classical monocytes was greater during HTMH compared to HTLH while TNFR2 expression was lower during HTLH compared to both MTMH and HTMH. Data suggest that exercise in the heat increases circulating TNF-α and STNFR1 concentration concomitantly. Furthermore, non-classical monocyte expression of TNFRs are impacted by temperature and humidity during exercise.

Changes in electrocardiogram parameters during acute nonshivering cold exposure and associations with brown adipose tissue activity, plasma catecholamine levels, and brachial blood pressure in healthy adults

BACKGROUND

Sympathetic activity causes changes in electrocardiogram (ECG) during cold exposure and the changes have been studied mostly during hypothermia and less during mild acute nonshivering cold exposure. Cold-induced sympathetic activity also activates brown adipose tissue (BAT) and increases arterial blood pressure (BP) and plasma catecholamine levels. We examined changes in ECG parameters during acute nonshivering cold exposure and their associations with markers of sympathetic activity during cold exposure: brachial blood pressure (BP), plasma catecholamine levels, and BAT activity measured by positron emission tomography (PET).

METHODS AND RESULTS

Healthy subjects (M/F = 13/24, aged 20-55 years) were imaged with [¹⁵ O]H₂ O (perfusion, N = 37) and [¹⁸ F]FTHA to measure plasma nonesterified fatty acid uptake (NEFA uptake, N = 37) during 2-h nonshivering cold exposure. 12-lead ECG (N = 37), plasma catecholamine levels (N = 17), and brachial BP (N = 31) were measured at rest in room temperature (RT) and re-measured after a 2-h nonshivering cold exposure. There were significant differences between RT and cold exposure in P axis (35.6 ± 26.4 vs. 50.8 ± 22.7 degrees, p = 0.005), PR interval (177.7 ± 24.6 ms vs.163.0 ± 28.7 ms, p = 0.001), QRS axis (42.1 ± 31.3 vs. 56.9 ± 24.1, p = 0.003), and QT (411.7 ± 25.5 ms vs. 434.5 ± 39.3 ms, p = 0.001). There was no significant change in HR, QRS duration, QTc, JTc, and T axis during cold exposure. Systolic BP (127.2 ± 15.7 vs. 131.8 ± 17.9 mmHg, p = 0.008), diastolic BP (81.7 ± 12.0 vs. 85.4 ± 13.0 mmHg, p = 0.02), and plasma noradrenaline level increased during cold exposure (1.97 ± 0.61 vs. 5.07 ± 1.32 µmol/L, p = 0.001). Cold-induced changes in ECG parameters did not correlate with changes in BAT activity, brachial BP, plasma catecholamines, or skin temperature.

CONCLUSIONS

During short-term nonshivering cold exposure, there were increases in P axis, PR interval, QRS axis, and QT compared to RT in healthy adults. Cold-induced changes in ECG parameters did not correlate with BAT activity, brachial BP, or plasma catecholamine levels which were used as markers of cold-induced sympathetic activity.

The influence of a hot environment on physiological stress responses in exercise until exhaustion

Exhaustive exercise in a hot environment can impair performance. Higher epinephrine plasma levels occur during exercise in heat, indicating greater sympathetic activity. This study examined the influence of exercise in the heat on stress levels. Nine young healthy men performed a maximal progressive test on a cycle ergometer at two different environmental conditions: hot (40°C) and normal (22°C), both between 40% and 50% relative humidity. Venous blood and saliva samples were collected pre-test and post-test. Before exercise there were no significant changes in salivary biomarkers (salivary IgA: p = 0.12; α-amylase: p = 0.66; cortisol: p = 0.95; nitric oxide: p = 0.13; total proteins: p = 0.07) or blood lactate (p = 0.14) between the two thermal environments. Following exercise, there were significant increases in all variables (salivary IgA 22°C: p = 0.04, 40°C: p = 0.0002; α-amylase 22°C: p = 0.0002, 40°C: p = 0.0002; cortisol 22°C: p = 0.02, 40°C: p = 0.0002; nitric oxide 22°C: p = 0.0005, 40°C: p = 0.0003, total proteins 22°C: p<0.0001, 40°C: p<0.0001 and; blood lactate 22°C: p<0.0001, 40°C: p<0.0001) both at 22°C and 40°C. There was no significant adjustment regarding IgA levels between the two thermal environments (p = 0.74), however the levels of α-amylase (p = 0.02), cortisol (p<0.0001), nitric oxide (p = 0.02) and total proteins (p = 0.01) in saliva were higher in the hotter conditions. Blood lactate was lower under the hot environment (p = 0.01). In conclusion, enduring hot temperature intensified stressful responses elicited by exercise. This study advocates that hot temperature deteriorates exercise performance under exhaustive stress and effort conditions.

Renal sympathetic nerve, blood flow, and epithelial transport responses to thermal stress

Thermal stress is a profound sympathetic stress in humans; kidney responses involve altered renal sympathetic nerve activity (RSNA), renal blood flow, and renal epithelial transport. During mild cold stress, RSNA spectral power but not total activity is altered, renal blood flow is maintained or decreased, and epithelial transport is altered consistent with a sympathetic stress coupled with central volume loaded state. Hypothermia decreases RSNA, renal blood flow, and epithelial transport. During mild heat stress, RSNA is increased, renal blood flow is decreased, and epithelial transport is increased consistent with a sympathetic stress coupled with a central volume unloaded state. Hyperthermia extends these directional changes, until heat illness results. Because kidney responses are very difficult to study in humans in vivo, this review describes and qualitatively evaluates an in vivo human skin model of sympathetically regulated epithelial tissue compared to that of the nephron. This model utilizes skin responses to thermal stress, involving 1) increased skin sympathetic nerve activity (SSNA), decreased skin blood flow, and suppressed eccrine epithelial transport during cold stress; and 2) increased SSNA, skin blood flow, and eccrine epithelial transport during heat stress. This model appears to mimic aspects of the renal responses. Investigations of skin responses, which parallel certain renal responses, may aid understanding of epithelial-sympathetic nervous system interactions during cold and heat stress.

Swimming in warm water is ineffective in heat acclimation and is non-ergogenic for swimmers

Heat acclimation (HA) in air confers adaptations that improve exercise capabilities in hot and possibly temperate air. Swimmers may benefit from HA, yet immersion may constrain adaptation. Therefore, we examined whether warm-water swimming constitutes effective HA. In a randomized-crossover study, eight male swimmers swam 60 min/day on 7 days in 33 °C (HA) or 28 °C (CON) water. They performed 20-min distance trials before and after each regime: in 33 °C water (Warm); 28 °C water (Temperate); and cycling in 29 °C air (Terrestrial) following standardized exercise. Rectal temperature (Tre ) rose ∼ 1 °C in HA sessions, and sweat loss averaged 1.4 L/h. After accounting for CON, HA did not confer any clear expansion of plasma volume [1.9% (95% CI: 7.7)], reduction in heart rate during standardized cycling exercise [1 b/min (9)], reduction in Tre during rest [+0.1 °C (0.1)] or exercise, or change in sudomotor function. Only perceived temperature and discomfort tended to improve. Performance was clearly not improved for Warm [+0.3% (1.8)] or Temperate [+0.3% (1.9)], was unclear for Terrestrial [+0.4% (17.7)], and was unrelated to changes in resting plasma volume (r < 0.3). In conclusion, short-term HA using swimming in 33 °C water confers little adaptation and is not ergogenic for warm or temperate conditions.

Time course of physiological and psychological responses in humans during a 20-day severe-cold-acclimation programme

The time course of physiological and psychological markers during cold acclimation (CA) was explored. The experiment included 17 controlled (i.e., until the rectal temperature reached 35.5°C or 170 min had elapsed; for the CA-17 session, the subjects (n = 14) were immersed in water for the same amount of time as that used in the CA-1 session) head-out water immersions at a temperature of 14°C over 20 days. The data obtained in this study suggest that the subjects exhibited a thermoregulatory shift from peripheral-to-central to solely central input thermoregulation, as well as from shivering to non-shivering thermogenesis throughout the CA. In the first six CA sessions, a hypothermic type of acclimation was found; further CA (CA-7 to CA-16) led to a transitional shift to a hypothermic–insulative type of acclimation. Interestingly, when the subjects were immersed in water for the same time as that used in the CA-1 session (CA-17), the CA led to a hypothermic type of acclimation. The presence of a metabolic type of thermogenesis was evident only under thermoneutral conditions. Cold-water immersion decreased the concentration of cold-stress markers, reduced the activity of the innate immune system, suppressed specific immunity to a lesser degree and yielded less discomfort and cold sensation. We found a negative correlation between body mass index and Δ metabolic heat production before and after CA.

Cold exposure enhances fat utilization but not non-esterified fatty acids, glycerol or catecholamines availability during submaximal walking and running

Cold exposure modulates the use of carbohydrates (CHOs) and fat during exercise. This phenomenon has mostly been observed in controlled cycling studies, but not during walking and running when core temperature and oxygen consumption are controlled, as both may alter energy metabolism. This study aimed at examining energy substrate availability and utilization during walking and running in the cold when core temperature and oxygen consumption are maintained. Ten lightly clothed male subjects walked or ran for 60-min, at 50% and 70% of maximal oxygen consumption, respectively, in a climatic chamber set at 0°C or 22°C. Thermal, cardiovascular, and oxidative responses were measured every 15-min during exercise. Blood samples for serum non-esterified fatty acids (NEFAs), glycerol, glucose, beta-hydroxybutyrate (BHB), plasma catecholamines, and serum lipids were collected immediately prior, and at 30- and 60-min of exercise. Skin temperature strongly decreased while core temperature did not change during cold trials. Heart rate (HR) was also lower in cold trials. A rise in fat utilization in the cold was seen through lower respiratory quotient (RQ) (-0.03 ± 0.02), greater fat oxidation (+0.14 ± 0.13 g · min(-1)) and contribution of fat to total energy expenditure (+1.62 ± 1.99 kcal · min(-1)). No differences from cold exposure were observed in blood parameters. During submaximal walking and running, a greater reliance on derived fat sources occurs in the cold, despite the absence of concurrent alterations in NEFAs, glycerol, or catecholamine concentrations. This disparity may suggest a greater reliance on intra-muscular energy sources such as triglycerides during both walking and running.

Divergent cytokine response following maximum progressive swimming in hot water

Exercise promotes transitory alterations in cytokine secretion, and these changes are affected by exercise duration and intensity. Considering that exercise responses also are affected by environmental factors, the goal of the present study was to investigate the effect of water temperature on the cytokine response to maximum swimming. Swiss mice performed a maximum progressive swimming exercise at 31 or 38°C, and plasma cytokine levels were evaluated immediately or 1, 6 or 24 h after exercise. The cytokine profile after swimming at 31°C was characterized by increased interleukin (IL)-6 and monocyte chemotactic protein-1 (MCP-1) levels, which peaked 1 h after exercise, suggesting an adequate inflammatory milieu to induce muscle regeneration. Transitory reductions in IL-10 and IL-12 levels also were observed after swimming at 31°C. The cytokine response to swimming was modified when the water temperature was increased to 38°C. Although exercise at 38°C also led to IL-6 secretion, the peak in IL-6 production occurred 6 h after exercise, and IL-6 levels were significantly lower than those observed after maximum swimming at 31°C (p = 0·030). Furthermore, MCP-1 levels were lower and tumour necrosis factor-α levels were higher immediately after swimming at 38°C, suggesting a dysregulated pro-inflammatory milieu. These alterations in the cytokine profile can be attributed in part to reduced exercise total work because exhaustion occurred sooner in mice swimming at 38°C than in those swimming at 31°C.

Research methodology: endocrinologic measurements in exercise science and sports medicine

OBJECTIVE

To provide background information on methodologic factors that influence and add variance to endocrine outcome measurements. Our intent is to aid and improve the quality of exercise science and sports medicine research endeavors of investigators inexperienced in endocrinology.

BACKGROUND

Numerous methodologic factors influence human endocrine (hormonal) measurements and, consequently, can dramatically compromise the accuracy and validity of exercise and sports medicine research. These factors can be categorized into those that are biologic and those that are procedural-analytic in nature.

RECOMMENDATIONS

Researchers should design their studies to monitor, control, and adjust for the biologic and procedural-analytic factors discussed within this paper. By doing so, they will find less variance in their hormonal outcomes and thereby will increase the validity of their physiologic data. These actions can assist the researcher in the interpretation and understanding of endocrine data and, in turn, make their research more scientifically sound.

Catecholamines and the effects of exercise, training and gender

Stress hormones, adrenaline (epinephrine) and noradrenaline (norepinephrine), are responsible for many adaptations both at rest and during exercise. Since their discovery, thousands of studies have focused on these two catecholamines and their importance in many adaptive processes to different stressors such as exercise, hypoglycaemia, hypoxia and heat exposure, and these studies are now well acknowledged. In fact, since adrenaline and noradrenaline are the main hormones whose concentrations increase markedly during exercise, many researchers have worked on the effect of exercise on these amines and reported 1.5 to >20 times basal concentrations depending on exercise characteristics (e.g. duration and intensity). Similarly, several studies have shown that adrenaline and noradrenaline are involved in cardiovascular and respiratory adjustments and in substrate mobilization and utilization. Thus, many studies have focused on physical training and gender effects on catecholamine response to exercise in an effort to verify if significant differences in catecholamine responses to exercise could be partly responsible for the different performances observed between trained and untrained subjects and/or men and women. In fact, previous studies conducted in men have used different types of exercise to compare trained and untrained subjects in response to exercise at the same absolute or relative intensity. Their results were conflicting for a while. As research progressed, parameters such as age, nutritional and emotional state have been found to influence catecholamine concentrations. As a result, most of the recent studies have taken into account all these parameters. Those studies also used very well trained subjects and/or more intense exercise, which is known to have a greater effect on catecholamine response so that differences between trained and untrained subjects are more likely to appear. Most findings then reported a higher adrenaline response to exercise in endurance-trained compared with untrained subjects in response to intense exercise at the same relative intensity as all-out exercise. This phenomenon is referred to as the 'sports adrenal medulla'. This higher capacity to secrete adrenaline was observed both in response to physical exercise and to other stimuli such as hypoglycaemia and hypoxia. For some authors, this phenomenon can partly explain the higher physical performance observed in trained compared with untrained subjects. More recently, these findings have also been reported in anaerobic-trained subjects in response to supramaximal exercise. In women, studies remain scarce; the results are more conflicting than in men and the physical training type (aerobic or anaerobic) effects on catecholamine response remain to be specified. Conversely, the works undertaken in animals are more unanimous and suggest that physical training can increase the capacity to secrete adrenaline via an increase of the adrenal gland volume and adrenaline content.

The effects of single and repeated bouts of soccer-specific exercise on salivary IgA

OBJECTIVE

Athletes frequently train with a short time recovery between sessions. The present aim was to establish how salivary IgA is altered following two soccer-specific intermittent exercise bouts performed on the same day.

DESIGN

Ten males participated in two experimental trials (single session, double session) 1 week apart, in a counterbalanced design. One trial entailed afternoon exercise only (PMEX), in which participants completed soccer-specific intermittent exercise starting at 14:30h. On the other occasion, participants performed two bouts of exercise [starting at 10:30h (AMEX(1)) and at 14:30h (PMEX(2))]. Timed unstimulated saliva samples were collected before and immediately after exercise.

RESULTS

Mean salivary IgA levels increased significantly immediately post-exercise in the single afternoon trial (PMEX). Performance of a second soccer-specific exercise bout in 1 day elicited an increase in heart rate and perceived exertion, compared with the single session, but did not appear to suppress salivary IgA outcomes. Performing soccer-specific exercise at these different times of day did not affect the salivary IgA concentration and secretion rate or salivary cortisol in the short term.

CONCLUSIONS

These findings suggest that, two 90-min exercise sessions performed at a moderate intensity with a 2.25h rest in between do not necessarily have adverse effects on salivary IgA levels.

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 degrees 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 approximately 4 degrees C for the 60 min duration (CON, 36.5 +/- 0.1 degrees C; FC, 35.7 +/- 0.1 degrees C; P < 0.05) but core temperature rose by only approximately 0.25 degrees 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 (approximately 10%) has a disproportionately large effect on the hormonal and perceptual responses to heat stress.

Exercising in the cold inhibits growth hormone secretion by reducing the rise in core body temperature

OBJECTIVE

Ambient temperature alters exercise induced GH secretion. It is unknown whether temperature affects GH secretion at exercise intensities above the anaerobic threshold when other factors may override the relationship seen at lower intensities.

DESIGN

Cross-over study of ambient temperature on exercise induced GH in swimmers and rowers.

SETTING

St Thomas Hospital, London.

SUBJECTS

Ten healthy men (age 21.7+/-0.8 yrs). Five swimmers and five rowers.

INTERVENTION

Forty-minute exercise test at 105% of anaerobic threshold at room temperature (RT) and at 4 degrees C.

MEASUREMENTS

Cutaneous and core body temperature. Serum GH concentration.

RESULTS

Cutaneous body temperature increased during exercise at RT but decreased in the cold. Although core temperature rose in both settings, the rise was greater at RT (p=0.021). GH increased at both temperatures but the onset was delayed by the cold. Peak GH tended to be higher at RT (17.4+/-3.6 microg/L vs. 9.5+/-1.5 microg/L, p=0.07). Total GH secretion was greater at RT (353.3+/-99.1 microg min/L) than 4 degrees C (128.3+/-21.0 microg min/L), p=0.038. Change in core temperature correlated with log peak GH (r=0.66, p=0.039) and log incremental GH (r=0.67, p=0.032) when exercising at 4 degrees C. There was no difference between swimmers and rowers.

CONCLUSIONS

Exercise at 4 degrees C reduces GH secretion during exercise at intensities above the anaerobic threshold. A change in core body temperature may be one mechanism by which exercise induces GH secretion. The difference in GH between swimmers and rowers during their respective events relates to the conditions under which they compete.

Exercising in Environmental Extremes

Athletes, military personnel, fire fighters, mountaineers and astronauts may be required to perform in environmental extremes (e.g. heat, cold, high altitude and microgravity). Exercising in hot versus thermoneutral conditions (where core temperature is > or = 1 degrees C higher in hot conditions) augments circulating stress hormones, catecholamines and cytokines with associated increases in circulating leukocytes. Studies that have clamped the rise in core temperature during exercise (by exercising in cool water) demonstrate a large contribution of the rise in core temperature in the leukocytosis and cytokinaemia of exercise. However, with the exception of lowered stimulated lymphocyte responses after exercise in the heat, and in exertional heat illness patients (core temperature > 40 degrees C), recent laboratory studies show a limited effect of exercise in the heat on neutrophil function, monocyte function, natural killer cell activity and mucosal immunity. Therefore, most of the available evidence does not support the contention that exercising in the heat poses a greater threat to immune function (vs thermoneutral conditions). From a critical standpoint, due to ethical committee restrictions, most laboratory studies have evoked modest core temperature responses (< 39 degrees C). Given that core temperature during exercise in the field often exceeds levels associated with fever and hyperthermia (approximately 39.5 degrees C) field studies may provide an opportunity to determine the effects of severe heat stress on immunity. Field studies may also provide insight into the possible involvement of immune modulation in the aetiology of exertional heat stroke (core temperature > 40.6 degrees C) and identify the effects of acclimatisation on neuroendocrine and immune responses to exercise-heat stress. Laboratory studies can provide useful information by, for example, applying the thermal clamp model to examine the involvement of the rise in core temperature in the functional immune modifications associated with prolonged exercise. Studies investigating the effects of cold, high altitude and microgravity on immunity and infection incidence are often hindered by extraneous stressors (e.g. isolation). Nevertheless, the available evidence does not support the popular belief that short- or long-term cold exposure, with or without exercise, suppresses immunity and increases infection incidence. In fact, controlled laboratory studies indicate immuno-stimulatory effects of cold exposure. Although some evidence shows that ascent to high altitude increases infection incidence, clear conclusions are difficult to make because of some overlap with the symptoms of acute mountain sickness. Studies have reported suppressed cell-mediated immunity in mountaineers at high altitude and in astronauts after re-entering the normal gravity environment; however, the impact of this finding on resistance to infection remains unclear.

Pituitary and autonomic responses to cold exposures in man

This review presents hormonal responses to various cold exposures and their calorigenic effects in man and some animals. Previous studies in rats have shown that cold exposures activate the hypothalamic-pituitary-thyroid axis. Increased thyroid hormone concentrations lead to heat production via general stimulation of metabolism (obligatory thermogenesis) and possibly via activation of thyroid hormone receptors and uncoupling protein 1 (UCP 1) and deiodinase enzyme genes in the brown adipose tissue (BAT). In human subjects long-term cold exposures do not seem to activate the pituitary-thyroid axis, but rather accelerate the elimination of triiodothyronine (T3), leading to low serum concentrations of free T3 hormone. In corollary to this a hypothyreotic condition with increased serum thyroid-stimulating hormone and impaired mood and cognitive performance can be observed after long-term cold exposures such as wintering. During cold exposures the sympathetic nerve system is activated and noradrenaline is released to blood circulation and to BAT, where it leads to production of cAMP, lipolysis and free fatty acids. Free fatty acids open the mitochondrial proton channel protein in BAT. Protons enter the mitochondria and inhibit ATP synthesis (uncoupling). By this way energy is transformed into heat (facultatory or adaptive thermogenesis). In adult human subjects the amount of BAT is small and adaptive thermogenesis (non-shivering thermogenesis) has a smaller role. UCP 1 with other uncoupling proteins may have other functions in the control of body weight, sugar balance and formation of reactive oxygen species.

Salivary IgA response to prolonged exercise in a hot environment in trained cyclists

The aim of this study was to determine the effects of prolonged exercise in hot conditions on saliva IgA (s-IgA) responses in trained cyclists. On two occasions, in random order and separated by 1 week, 12 male cyclists cycled for 2 h on a stationary ergometer at 62 (3)% V(.)O(2 max) [194 (4) W; mean (SEM)], on one occasion (HOT: 30.3 degrees C, 76% RH) and on another occasion (

CONTROL

20.4 degrees C, 60% RH). Water was available ad-libitum. Venous blood samples and 2-min whole unstimulated saliva samples were collected at pre, post and 2 h post-exercise. The s-IgA concentration was determined using a sandwich-type ELISA. Exercising heart rate, rating of perceived exertion, rectal temperature, corrected body mass loss (P<0.01) and plasma cortisol (P<0.05) were greater during HOT. The decrease in plasma volume post-exercise was similar on both trials [HOT: -6.7 (1.1) and

CONTROL

-6.6 (1.3)%; P<0.01]. Saliva flow rate decreased post-exercise by 43% returning to pre-exercise levels by 2 h post-exercise (P<0.05) with no difference between trials. Saliva IgA concentration increased post-exercise (P<0.05) with no difference between trials. Saliva IgA secretion rate decreased post-exercise by 34% returning to pre-exercise levels by 2 h post-exercise (P<0.05) with no difference between trials. These data show that a prolonged bout of exercise results in a reduction in s-IgA secretion rate. Additionally, these data demonstrate that performing prolonged exercise in the heat, with ad libitum water intake, does not influence s-IgA responses to prolonged exercise.

Growth hormone and prolactin responses during partial and whole body warm-water immersions

AIM

To elucidate the role of core and skin thermoreceptors in the release of growth hormone (GH) and prolactin (PRL), a sequence of two experiments using whole-body (head-out) and partial (one forearm) hot water immersions was performed.

METHODS

Experiment 1: Nine healthy men were exposed to head-out and partial water immersions (25 min, 38-39 degrees C).

RESULTS

Head-out immersion increased the core temperature (38.0 +/- 0.1 vs. 36.7 +/- 0.1 degrees C, P < 0.001) and plasma concentration of the hormones (GH, 16.1 +/- 4.5 vs. 1.2 +/- 0.4 ng mL(-1), P < 0.01; PRL, 9.1 +/- 1.0 vs. 6.4 +/- 0.4 ng mL(-1), P < 0.05). During the partial immersion the core temperature was slightly elevated (36.8 +/- 0.1 vs. 36.6 +/- 0.1, P < 0.001), the concentration of GH increased (4.8 +/- 1.7 vs. 0.6 +/- 0.3, P < 0.05), while plasma PRL decreased (7.6 +/- 0.8, 6.0 +/- 0.6, 5.2 +/- 0.6, P < 0.01). Experiment 2: Seven volunteers immersed one forearm once in 39 degrees C and once in 38 degrees C water. The measurements were performed in 5-min intervals. The GH concentration increased gradually from the beginning of the immersions (min 10; 39 degrees C: 1.9 +/- 1.0 vs. 0.6 +/- 0.3 ng mL(-1), P < 0.01; 38 degrees C: 0.19 +/- 0.03 vs. 0.14 +/- 0.03, P < 0.05) and peaked after their completion (39 degrees C: +10 min, 3.7 +/- 2.0, P < 0.001; 38 degrees C: +15 min, 0.86 +/- 0.61, P < 0.01). The core temperature was unchanged until min 15 of the 39 degrees C bath. Thereafter, it increased about 0.15 degrees C above the baseline (P < 0.01). Immersion in 38 degrees C water did not induce core temperature changes.

CONCLUSIONS

Peripheral thermoreceptors are involved in GH release when the body is exposed to elevated environmental temperature while a substantial elevation of core temperature is a precondition of PRL release.

Body temperature, oxygen uptake and heart rate during walking in water and on land at an exercise intensity based on RPE in elderly men

The purpose of this study was to clarify the characteristics of the physiological response that occurs while walking in water and on land at an exercise intensity based on the rating of perceived exertion (RPE) in elderly men. Nine elderly men ranging from 66-70 years of age participated in this study as subjects. The actual trials consisted of walking for 20 minutes in 31 degrees C and 35 degrees C water on an underwater treadmill. The water depth of the treadmill corresponded to the level of the xiphoid process in the subject. The same subjects performed on-land walking using a moving belt treadmill for 20 minutes at a room temperature of 27 degrees C. The exercise intensity during walking in the two water trials and the on-land trial was the same "somewhat hard" measured on the basis of the subject's RPE rating of 13. There was no significant difference between the subjects' rectal temperatures among the three trials. The mean skin temperature and mean body temperature while walking for 20 minutes in 35 degrees C water were significantly higher (P<0.01) than in 31 degrees C water and on land. There were no significant differences in oxygen uptake and heart rate among the two trials in water and the on-land trial. The above results suggest that the exercise intensity based on a subject's RPE may be an effective index for the prescription of thermoneutral water walking in the same way that it is for land walking in the elderly.

Alterations in energy metabolism during exercise and heat stress

Much of the research that has examined the interaction between metabolism and exercise has been conducted in comfortable ambient conditions. It is clear, however, that environmental temperature, particularly extreme heat, is a major practical issue one must consider when examining muscle energy metabolism. When exercise is conducted in very high ambient temperatures, the gradient for heat dissipation is significantly reduced which results in changes to thermoregulatory mechanisms designed to promote body heat loss. This can ultimately impact upon hormonal and metabolic responses to exercise which act to alter substrate utilisation. In general, the literature examining metabolic responses to exercise and heat stress has demonstrated a shift towards increased carbohydrate use and decreased fat use. Although glucose production appears to be augmented during exercise in the heat, glucose disposal and utilisation appears to be unaltered. In contrast, glycogen use has been consistently demonstrated to be augmented during exercise in the heat. This increase in glycogenolysis is observed via both aerobic and anaerobic pathways. Although several hypotheses have been proposed as mechanisms for the substrate shift towards greater carbohydrate metabolism during exercise and heat stress, recent work suggests that an augmented sympatho-adrenal response and intramuscular temperature may be responsible for such a phenomenon.

Thermoregulatory responses to low-intensity prolonged swimming in water at various temperatures and treadmill walking on land

The purpose of the present study was to examine the effect of water temperature on the human body during low-intensity prolonged swimming. Six male college swimmers participated in this study. The experiments consisted of breast stroke swimming for 120 minutes in 23 degrees C, 28 degrees C and 33 degrees C water at a constant speed of 0.4 m.sec-1 in a swimming flume. The same subjects walked on a treadmill at a rate of approximately 50% of maximal oxygen uptake (VO2max) at the same relative intensity as the three swimming trials. Rectal temperature (Tre) in 33 degrees C water was unchanged during swimming for 120 minutes. Tre during treadmill walking increased significantly compared to the three different swimming trials. Tre, mean skin temperature (Tsk) and mean body temperature (Tb) in 23 degrees C and 28 degrees C water decreased significantly more than in both the 33 degrees C water and walking on land. VO2 during swimming in 23 degrees C water increased more than during swimming in the 28 degrees C and 33 degrees C trials; however, there were no significant differences in VO2 between the 23 degrees C swimming trial and treadmill walking. Heart rate (HR) during treadmill walking on land increased significantly compared with HR during the three swimming trials. Plasma adrenaline concentration at the end of the treadmill walking was higher than that at the end of each of the three swimming trials. Noradrenaline concentrations at the end of swimming in the 23 degrees C water and treadmill walking were higher than those during the other two swimming trials. Blood lactate concentration during swimming in 23 degrees C water was higher than that during the other two swimming trials and walking on land. These results suggest that the balance of heat loss and heat production is maintained in the warm water temperature. Therefore, a relatively warm water temperature may be desirable when prolonged swimming or other water exercise is performed at low intensity.

Lifestyle, stress and cortisol response: Review II : Lifestyle

To prevent lifestyle related diseases, it is important to modify lifestyle behavior. The control of mental stress level and prevention of mental stress-related diseases have become one of the most important problems in Japan. To check mental stress level objectively during the early stage of stress-related diseases and determine appropriate coping methods, it is necessary to design a useful index for mental stress. Cortisol is a steroid hormone secreted by the adrenal cortex. This is an essential hormone to human survival, and plays a key role in adaptation to stress. In another review, we concluded that cortisol appears to be an adequate index for mental stress.However, lifestyle factors such as alcohol drinking, smoking, lack of exercise etc., are strongly associated with mental stress. Thus, in this review, we focus on the relationship between cortisol and lifestyle.The present findings suggested that lifestyle factors; smoking, alcohol drinking, exercise, sleep and nutrition are strongly associated with cortisol levels, and it may be impossible to determine whether alterations in cortisol levels are due to mental stress.It was suggested that those lifestyle effects on not only mental stress itself but also cortisol levels should be considered, when assessing mental stress by cortisol levels.

Effect of precooling on high intensity cycling performance

OBJECTIVE

To examine the effects of precooling skin and core temperature on a 70 second cycling power test performed in a warm and humid environment (29 degrees C, 80% relative humidity).

METHODS

Thirteen male national and international level representative cyclists (mean (SD) age 24.1 (4.1) years; height 181.5 (6.2) cm; weight 75.5 (6.4) kg; maximal oxygen uptake (VO2peak) 66.1 (7.0) ml/kg/min) were tested in random order after either 30 minutes of precooling using cold water immersion or under control conditions (no precooling). Tests were separated by a minimum of two days. The protocol consisted of a 10 minute warm up at 60% of VO2peak followed by three minutes of stretching. This was immediately followed by the 70 second power test which was performed on a standard road bicycle equipped with 172.5 mm powermeter cranks and mounted on a stationary ergometer.

RESULTS

Mean power output for the 70 second performance test after precooling was significantly (p<0.005) increased by 3.3 (2.7)% from 581 (57) W to 603 (60) W. Precooling also significantly (p<0.05) decreased core, mean body, and upper and lower body skin temperature; however, by the start of the performance test, lower body skin temperature was no different from control. After precooling, heart rate was also significantly lower than control throughout the warm up (p<0.05). Ratings of perceived exertion were significantly higher than the control condition at the start of the warm up after precooling, but lower than the control condition by the end of the warm up (p<0.05). No differences in blood lactate concentration were detected between conditions.

CONCLUSIONS

Precooling improves short term cycling performance, possibly by initiating skin vasoconstriction which may increase blood availability to the working muscles. Future research is required to determine the physiological basis for the ergogenic effects of precooling on high intensity exercise.

The physiology and biomechanics of competitive swimming

Fast swimming, either in the pool, in open water swimming, or in water polo and synchronized swimming, requires maximizing the efficiencies with which the human body can move through a liquid medium. A multitude of factors can affect the ability to swim fast as well as the final outcome. Physiology and biomechanics are the present tools used by sports scientists to determine which factors are important to fast swimming and, subsequently, to determine how the swimmer may maximize these factors to improve performance.

The response on glucoregulatory hormones of in vivo whole body hyperthermia

This study was designed to examine the effects of in vivo hyperthermia on the circulating concentrations of a number of glucoregulatory hormones potentially involved in immunomodulation. Eight healthy male volunteers were immersed for 2 h in a hot water bath (water temperature 39.5 degrees C) (WI) during which period their rectal temperature rose to 39.5 degrees C. In a control study the subjects were immersed in thermoneutral water (water temperature 34.5 degrees C). Blood samples were collected before, at body temperature 38 degrees C (42.5 (30-52), median and range), minutes of hot WI, 39 degrees C (72.5 (58-97) minutes of hot WI), and 39.5 degrees C (at the end of 2 h of hot WI), as well as 1 and 2 h after cessation of 2 h of hot WI. In the control experiment blood samples were collected at identical time points. The growth hormone concentrations were elevated already at 38 degrees C to 24.2 (3.9-55.0) mU/l and peaked at 39 degrees C to 48.4 (20.8-81.5) mU/l compared to 0.3 (0.3-9.0) mU/l at baseline; at 39.5 degrees C the concentration declined to 31.6 (13.0-48.0) mU/l and further to 7.4 (0.8-17.3) mU/l 1 h after ending hot WI. The beta-endorphin levels were augmented at 39 degrees C and 39.5 degrees, to 8.0 (3.4-27.8) pmol/l and 8.1 (3.1-44.6) pmol/l, respectively, from 2.2 (0.7-5.6) pmol/l baseline. Glucagon levels raised from 23.0 (12.0-32.0) pmol/l to 32.0 (24.0-52.0) pmol/l at 39 degrees C, and to 38.5 (26.0-57.0) pmol/l at 39.0 degrees C. Insulin levels remained unchanged. Plasma glucose increased from 4.75 (4.2-7.6) mmol/l to 5.20 (4.6-5.6) mmol/l alone after 90 min of WI (temperature 39-39.5 degrees C). It is concluded that in vivo whole body WI hyperthermia increases the circulating levels of several essential glucoregulatory hormones.

Mild overcooling increases energy expenditure during endurance exercise

Intensive cooling has been shown to increase energy expenditure (EE) during work as well as to decrease physical performance. Two different levels of moderate cooling (10 degrees C vs 15 degrees C) were studied during light endurance exercise in order to examine the effect of the increased heat loss on EE. Twelve subjects performed a 90-min low intensity exercise (100 W) on a cycle ergometer, wearing a water-cooled calorimeter suit for controlled cooling. The lower temperature resulted in a 4.3 +/- 3.8% (mean +/- SD) higher EE, increased total heat loss and lowered skin temperatures. No differences in central core body temperature, heart rate or respiratory quotient (RQ) were recorded. There was a relation between differences in the rate of heat loss and the corresponding increase in EE. Even a small increase in cooling during endurance exercise increased EE which may be a relevant problem in winter sports.

Plasma TSH, T3, T4 and cortisol responses to swimming at varying water temperatures

The acute effect of 30-min swimming at a moderate speed, at three water temperatures (20, 26 and 32 degrees C) on plasma thyroid stimulating hormone (TSH), free thyroxine (F.T4), triiodothyronine (T3) and cortisol concentrations was studied in 15 élite male swimmers. Blood was sampled before and immediately after the events. The heart rate, which was continuously monitored during exercise, had the highest response at 32 degrees C and the lowest at 20 degrees C. Blood lactate concentrations were found to be similar after the three tests. Plasma TSH and F.T4 were found to be significantly increased (by 90.4% and 45.7% respectively) after swimming at 20 degrees C, decreased at 32 degrees C (by 22.3% and 10.1% respectively) and unchanged at 26 degrees C. Exercise at these three water temperatures did not significantly affect T3. Finally, plasma cortisol was found to be increased after swimming at 32 degrees C (by 82.8%) and 26 degrees C (by 46.9%), but decreased at 20 degrees C (by 6.1%).

Metabolic, body temperature and hormonal responses to repeated periods of prolonged cycle-ergometer exercise in men

This study was designed to find out whether rest intervals and prevention of dehydration during prolonged exercise inhibit a drift in metabolic rate, body temperature and hormonal response typically occurring during continuous work. For this purpose in ten healthy men the heart rate (fc), rectal temperature (Tre), oxygen uptake (VO2), as well as blood metabolite and some hormone concentrations were measured during 2-h exercise at approximately 50% maximal oxygen uptake split into four equal parts by 30-min rest intervals during which body water losses were replaced. During each 30-min exercise period there was a rapid change in Tre and fc superimposed on which, these values increased progressively in consecutive exercise periods (slow drift). The VO2 showed similar changes but there were no significant differences in the respiratory exchange ratio, pulmonary ventilation, mechanical efficiency and plasma osmolality between successive periods of exercise. Blood glucose, insulin and C-peptide concentrations decreased in consecutive exercise periods, whereas plasma free fatty acid, glycerol, catecholamine, growth hormone and glucagon concentrations increased. Blood lactate concentrations did not show any regular drift and the plasma cortisol concentration decreased during the first two exercise periods and then increased. In conclusion, in spite of the relatively long rest intervals between the periods of prolonged exercise and the prevention of dehydration several physiological and hormonal variables showed a distinct drift with time. It is suggested that the slow drift in metabolic rate could have been attributable in the main to the increased concentrations of heat liberating hormones.

Influence of moderate cold exposure on blood lactate during incremental exercise

This study examined the effect of exposure of the whole body to moderate cold on blood lactate produced during incremental exercise. Nine subjects were tested in a climatic chamber, the room temperature being controlled either at 30 degrees C or at 10 degrees C. The protocol consisted of exercise increasing in intensity in 35 W increments every 3 min until exhaustion. Oxygen consumption (VO2) was measured during the last minute of each exercise intensity. Blood samples were collected at rest and at exhaustion for the measurement of blood glucose, free fatty acid (FFA), noradrenaline (NA) and adrenaline (A) concentrations and, during the last 15 s of each exercise intensity, for the determination of blood lactate concentration [la-]b. The VO2 was identical under both environments. At 10 degrees C, as compared to 30 degrees C, the lactate anaerobic threshold (Than,la-) occurred at an exercise intensity 15 W higher and [la-]b was lower for submaximal intensities above the Than,la-. Regardless of ambient temperature, glycaemia, A and NA concentrations were higher at exhaustion while FFA was unchanged. At exhaustion the NA concentration was greater at 10 degrees C [15.60 (SEM 3.15) nmol.l-1] than at 30 degrees C [8.64 (SEM 2.37) nmol.l-1]. We concluded that exposure to moderate cold influences the blood lactate produced during incremental exercise. These results suggested that vasoconstriction was partly responsible for the lower [la-]b observed for submaximal high intensities during severe cold exposure.

Contribution of hGH20K variant to blood hGH response in sauna and exercise

Exercise-induced increases in blood somatotropin (hGH) have always been considered in terms of quantity of the circulating molecules. Knowing that the hypophysis can release several GH species, we investigated the differential release in blood of total hGH (hGHT) and the main hGH variant (hGH20K) molecules in six trained male swimmers exposed to three different conditions known to favor GH release in blood: 45 min--70% maximum oxygen uptake (VO2max) bicycling and swimming, and 20 min of sauna bathing. Based on the binding specificity of hGH antibodies, hGH20K was isolated then assayed using the Nichols immunoradiometric assay system. All three experimental conditions produced significant (P less than 0.001) elevations in blood hGHT and hGH20K. In all three cases, mean blood hGH20K contribution to blood hGHT was relatively constant (11.9, SE 0.7%). Rises in rectal temperature were not statistically related to the changes in blood hGHT. This demonstration of a relatively constant elevation in hGH20K during bicycling, swimming, and sauna bathing can hardly explain the large differences in blood hGHT responses reported in literature under similar conditions.

Influence of cold exposure on blood lactate response during incremental exercise

This study examined the effect of acute exposure of the whole body to cold on blood lactate response during incremental exercise. Eight subjects were tested with a cycle ergometer in a climatic chamber, room temperature being controlled either at 24 degrees C (MT) or at -2 degrees C (CT). The protocol consisted of a step increment in exercise intensity of 30 W every 2 min until exhaustion. Oxygen consumption (VO2) was measured at rest and during the last minute of each exercise intensity. Blood samples were collected at rest and at exhaustion for estimations of plasma norepinephrine (NE), epinephrine (E), free fatty acid (FFA) and glucose concentrations, during the last 15 s of each exercise step and also during the 1st, 4th, 7th, and the 10th min following exercise for the determination of blood lactate (LA) concentration. The VO2 was higher during CT than during MT at rest and during nearly every exercise intensity. At CT, lactate anaerobic threshold (LAT), determined from a marked increase of LA above resting level, increased significantly by 49% expressed as absolute VO2, and 27% expressed as exercise intensity as compared with MT. The LA tended to be higher for light exercise intensities and lower for heavy exercise intensities during CT than during MT. The E and NE concentrations increased during exercise, regardless of ambient temperature. Furthermore, at rest and at exhaustion E concentrations did not differ between both conditions, while NE concentrations were greater during CT than during MT. Moreover, an increase off FFA was found only during CT.(ABSTRACT TRUNCATED AT 250 WORDS)

Physical stress and catecholamine release

In both health and disease, noradrenaline and adrenaline concentrations in plasma increase with intensity and duration of exercise (Figure 1). These changes are only to a minor extent due to decreased catecholamine clearance (Figure 2). The increase in sympathoadrenal activity during exercise is primarily elicited by feed-forward stimulation from motor centres in the brain (Figure 3, Table 1), and by afferent impulses from working muscles (Figure 4). During continued exercise, changes in internal milieu may enhance the catecholamine response. Of particular interest from a metabolic point of view is the fact that during exercise a decrease in plasma glucose causes a relatively large increase in plasma adrenaline (Figure 5). Sympathoadrenal activity is of major importance for exercise capacity. By depressing insulin secretion, as well as by direct effects on target tissues, sympathoadrenal activity enhances mobilization of glycogen as well as triglyceride from both extra- and intramuscular depots. After training, noradrenaline responses to given absolute work loads are reduced, while responses to given relative loads, i.e. work load in percent of individual work capacity, VO2/VO2max%, are unchanged. Prolonged endurance training may increase the size and secretory capacity of the adrenal medulla (Figure 7, Table 2), an adaptation which may improve exercise capacity. Differences in catecholamine levels cannot explain the fact that physically-active individuals have a lower cardiac mortality than inactive ones.

Accidental hypothermia. Review of the literature

The pathophysiology and treatment of accidental hypothermia are discussed. Special attention is paid to the pathophysiologic problems of rewarming. For severely hypothermic patients we would recommend peritoneal dialysis as the method of choice for rewarming in a hospital situation. In a "field situation" passive or slow active rewarming is recommended.