Effects of endurance training and heat acclimation on psychological strain in exercising men wearing protective clothing

Two experiments examined the influences of endurance training and heat acclimation on ratings of perceived exertion (RPE) and thermal discomfort (RTD) during exercise in the heat while wearing two types of clothing. In experiment 1, young men underwent 8 weeks of physical training [60-80% of maximal aerobic power (VO2max) for 30-45 min day-1, 3-4 days week-1 at 20-22 degrees C dry bulb (db) temperature] followed by 6 days of heat acclimation [45-55% VO2max for 60 min day-1 at 40 degrees C db, 30% relative humidity (rh)] (n = 7) or corresponding periods of control observation followed by heat acclimation (n = 9). In experiment 2, young men were heat-acclimated for 6 or 12 days (n = 8 each). Before and after each treatment, subjects completed bouts of treadmill exercise (1.34 m s-1, 2% grade in experiment 1 and 0% grade in experiment 2) in a climatic chamber (40 degrees C db, 30% rh), wearing in turn normal light clothing (continuous exercise at 37-45% VO2max for a tolerated exposure of 116-120 min in experiment 1 and at 31-34% VO2max for 146-150 min in experiment 2) or clothing protective against nuclear, biological, and chemical agents (continuous exercise at 42-51% VO2max for a tolerated exposure of 47-52 min in experiment 1 and intermittent exercise at 23% VO2max for 97-120 min in experiment 2). In experiment 1, when wearing normal clothing, endurance training and/or heat acclimation significantly decreased RPE and/or RTD at a fixed power output. There were concomitant reductions in relative work intensity (% VO2max) [an unchanged oxygen consumption (VO2) but an increased VO2max, or a reduced VO2 with no change of VO2max], rectal temperature (Tre), mean skin temperature (Tsk), and/or heart rate (HR). When wearing protective clothing, in contrast, there were no significant changes in RPE or RTD. Although training and/or acclimation reduced %VO2max or Tre, any added sweat that was secreted did not evaporate through the protective clothing, thus increasing discomfort after training or acclimation. Tolerance times were unchanged in either normal or protective clothing. In experiment 2, when wearing normal clothing, heat acclimation significantly decreased RPE and RTD at a fixed power output, with concomitant reductions in Tre, Tsk, and HR; the response was greater after 12 than after 6 days of acclimation, significantly so for RPE and HR. When wearing protective clothing, the subjects exercised at a lower intensity for a longer duration than in the moderate exercise trial. Given this tactic, either 6 or 12 days of heat acclimation induces significant reductions RPE and/or RTD, accompanied by reductions in Tre, Tsk, and/or HR. Tolerance times in protective clothing were also increased by 11-15% after acclimation, despite some increase of sweat accumulation in the protective clothing. The results suggest that (1) neither endurance training nor heat acclimation reduce psychological strain when protective clothing is worn during vigorous exercise, because increased sweat accumulation adds to discomfort, and (2) in contrast to the experience during more vigorous exercise, heat acclimation is beneficial to the subject wearing protective clothing if the intensity of effort is kept to a level that allows permeation of sweat through the clothing. This condition is likely to be met in most modern industrial applications.     

Physiological responses of men and women during exercise in hot environments with equivalent WBGT

Eight Japanese men and women participated in this study. They were randomly exposed to two environments: hot-dry; HD (Ta = 40 degrees C, rh 30%, wet bulb globe temperature (WBGT) = 32 degrees C) and hot-wet; HW (Ta = 31 degrees C, rh = 80%, WBGT = 32 degrees C) for 110 min. During the exposure, they rested on a bicycle ergometer for 20 min during rest and 30 min during recovery, then they pedaled it with an intensity of 40% VO2 max for 60 min. Tre, Tsk, and HR were recorded every minute. Total sweat loss and dripping were measured by independent bed balances which was connected to a computer processing with an accuracy of 1 g throughout the experiment. Sweat sodium concentration at forearm and back sites were collected by sweat capsule technique. These results showed that delta Tre, Tsk, evaporated sweat, dripping sweat, body heat storage of both sexes in HD were significantly higher than these in HW during exercise. HR of men in HD at the end of recovery was slightly higher than that of women. Whereas the sweat sodium concentration at forearm and back sites in both sexes remained unchanged either in HD or HW environment, it was found that HD was more stressful than HW environment under equivalent WBGT.     

Automated information systems in surgery and resuscitation]

Ten heat-acclimated females exercised seminude on a treadmill at 30% Vo2 max (M=152 W-m-2) under eight air temperatures (Ta) ranging from 30 degrees C to 52 degrees C. Each experiment involved 1 h of fixed and a 2nd h of progressively increasing water vapor pressure (Pw) with either air movement of 1 m-s-1 or still air. The equilibrium values of rectal temperature (Tre), mean skin temperature (Tsk),and heart rate (HR) reached in the 1st h were forced upwards in the 2nd h by the rising Pw. The critical Pw was defined by the Tre inflection point for each Ta. The loci of the critical Pw were used to delineate the thermal limits on the psychrometric chart and were used to derive the effective evaporative coefficient (Ke') applicable to the ambient capacity for evaporative cooling (Emax). The derived Ke' was 17.6 +/- 4.2 W-m-2 (mean +/- SD) for v0.6m-s-1. Isotherms constructed on the basis of the obtained Ké, Tsk, and sweating capacity were higher than the physiologically based Pw limits.     

Ambient temperature effects on thermoregulation and endurance in anticholinesterase-treated rats

In sedentary animals, physostigmine (PH) administration resulted in a decreased core temperature that is ambient temperature (Ta) dependent. PH administration in rats exercising on a treadmill (26 degrees C, 50% rh, 11m/min, 6 degrees incline) decremented endurance and increased rate of rise of core temperature (heating rate, HR). This study was undertaken to examine the effects of Ta on the endurance and thermoregulatory decrements of PH-treated running rats. Adult male rats (510-530g) were given either 0.2ml saline (C) or 100 ug/kg physostigmine salicylate in 0.2 ml saline via tail vein 15 min prior to the start of running to exhaustion at 10, 15, 26, or 30 degrees C. In both C- and PH-treated groups, endurance decreased and HR increased with increasing Ta from 15 to 30 degrees C. At 15 and 26 degrees C the C rats ran significantly (p < .05) longer and had significantly lower HR than the PH rats: C15 = 90 +/- 8 min, 0.022 +/- 0.006 degrees C/min; C26 = 67 +/- 6, 0.051 +/- 0.007; PH15 = 57 +/- 5, 0.052 +/- 0.008; and PH26 = 43 +/- 6, 0.092 +/- 0.007. At 10 and 30 degrees C there were no significant differences between C and PH-treated rats. A Ta of 30 degrees C was too high for effective cooling in either group, and at 10 degrees C both groups were able to dissipate heat despite the increased metabolic rate of the PH-treated rats. The PH-treated rat model of cholinergic drug effect is useful at a Ta of 15 and 26 degrees C.     

Clinical implications of penicillin and ceftriaxone resistance among children with pneumococcal bacteremia

BACKGROUND: The influence of non-ionic osmols on thermoregulation is unclear. HYPOTHESIS: Hyperglycemia will attenuate the rise in exercise core temperature. METHODS: Dehydrated by 4-h of water immersion (34.5 degrees C) to the neck, 6 men, (35+/-SD 7 yr) participated in each of three trials where 2.0 g x kg(-1) body wt of oral glucose (33.8% weight per volume) was consumed followed by 80 min supine rest (Glu/Rest), or 70 min supine cycle exercise at 62.8%+/-SE 0.5% (1.97+/-0.02 L x min(-1)) peak O2 uptake, followed by 10 min supine recovery with prior (Glu/Ex) or without glucose (No Glu/Ex) ingestion. Blood samples were taken periodically for measurement of Hb, Hct, Na+, K+, Osm, and glucose; mean skin (Tsk) and rectal (Tre) temperatures, and sweating rate (resistance hygrometry) and skin blood velocity (laser Doppler) were measured intermittently. RESULTS: Mean percent changes in plasma volume (p<0.05) for the exercise trials were not different: -12.3+/-2.2% (No Glu/Ex) and -12.1+/-2.1% (Glu/Ex). Mean (+/-SE) pre-exercise plasma [glucose] for Glu/Ex was higher than that of No Glu/Ex (108.4+/-3.9 vs. 85.6+/-1.6 mg x dL(-1), respectively, p<0.05). Glu/Ex vs. No Glu/Ex data, respectively, at the end of exercise indicated that: Tre was lower by 0.4 degrees C (38.2+/-0.2 vs. 38.6+/-0.1 degrees C, p<0.05), Tsk was lower (32.0+/-0.3 vs. 32.4+/-0.2 degrees C, p<0.05), forearm sweating rate was lower (0.94+/-0.09 vs. 1.05+/-0.07 mg x cm(-2) x min(-1), p<0.05); and head (temporal) skin blood velocity was not different (1.67+/-0.21 vs. 1.51+/-0.24 Hz x 10(3), NS). CONCLUSIONS: Elevation of plasma [glucose] prior to supine submaximal exercise in dehydrated men attenuates the increase of Tre without alteration of heat production, total body sweating, serum electrolytes and osmolality, or exercise-induced hypoglycemia: the mechanism may be enhanced peripheral blood flow that could enhance body heat loss.     

Physiological responses to simulated rock climbing at different angles

PURPOSE: Although rock climbing has increased in popularity as a recreational activity and competitive sport, few studies have assessed the physiological demands of the activity. To describe the physiological responses to rock climbing at different angles. METHODS: Sixteen experienced climbers (age = 26 +/- 8 yr) attempted intermittent climbing bouts at different angles on a special rock climbing treadmill (Brewer's Ledge Treadwall). Heart rate (HR) was monitored continuously, and VO2 was determined at 20-s intervals during each climbing bout. Immediately after each bout, the subject provided a rating of perceived exertion (RPE), and an average of right and left handgrip force (HG) was obtained. Blood was collected via fingerprick after each bout and analyzed for lactate (BL). On a separate day, each subject completed a steady-state treadmill running bout at a HR equal to that obtained at an 86 degree angle during the climbing test. This test was followed by a progression to exhaustion to determine peak HR and VO2 responses. RESULTS: While HR increased with climbing angle, VO2 did not significantly vary. BL began to significantly increase as the angle exceeded vertical (91 degrees) and continued to increase with successive angles. HG decreased with increasing angle and was negatively correlated with BL (r = -0.96). Scores for RPE increased with steeper angles. The comparison of steady-state work at the same HR for climbing versus treadmill running revealed a higher VO2 during running with no differences in BL and RPE. CONCLUSIONS: Based upon these results, it was concluded that continuous rock climbing over terrain steepness of 80 degrees to 102 degrees presents a "very heavy" work challenge, averaging 8.4-9.0 metabolic equivalents, regardless of angle. Despite similar RPE and BL, the relative exercise intensity elicited from simulated rock climbing is lower than that of running at the same HR.     

Mechanisms of temperature regulation in heat-acclimated hamsters

Mechanisms of temperature regulation were assessed by measurements of oxygen consumption (VO2), body temperature (Rre = rectal, Tsk = skin), evaporative water loss (EWL), regional distribution of blood flow, and blood volume. Hamsters (Mesocricetus auratus) were acclimated to ambient temperatures of 34 or 22 degrees C. VO2 of 34 degrees C-exposed animals was reduced to 50% of that of controls at 22 degrees C, whereas EWL with heat exposure was almost double that of controls. Heat-acclimated animals had a slightly elevated Tre in comparison to 22 degrees C-acclimated animals, whereas there was a marked elevation in Tsk with heat exposure, in contrast to control animals at 22 degrees C. Blood flow distribution measurements indicated that with 34 degrees C exposure there was a decreased flow in liver, kidney, and intestine, whereas there was an increase to the carcass. Red cell and plasma volumes in heat-acclimated hamsters were decreased belwo the values of the 22 degrees C controls. Heat acclimation of the fhamster appears to involve reduced VO2 and increased WEL. Convective and radiative heat loss appear to be maintained by increased Tsk with heat exposure. Nonevaporative heat dissipation mechanisms are of primary importance in thermoregulation of the heat-acclimated hamster, and it is suggested that this is mediated by increased peripheral blood flow with reduced flow to the viscera.     

Effects of head-out water immersion on cardiorespiratory responses to maximal cycling exercise

Our objectives were to determine effects of head-out immersion (HOI), scuba breathing, and water temperature on cardiorespiratory responses to maximal aerobic work. Measurements of VO2, VE, and heart rate (HR) were obtained on seven men (27 yr, 177 cm, 67 kg) as they performed the same upright bicycling exercise to exhaustion (4-5 min) in 23 degrees C air and 30 degrees C water. Maximal oxygen uptake (VO2 max) during HOI was 3.18 liters - min-1, which was not statistically different from the mean of 3.29 liters- min-1 in air. When compressed air was breathed via scuba during HOI, VO2 max was 3.12 liters- min-1 and not significantly different from that when room air was breathed and a low-resistance valve in water was used. HOI decreased VE by 15.7 liters - min-1 and HR by 10 beats (b) - min-1. Scuba breathing further reduced VE by 22.0 liters - min-1. Similar measurements were made on four of the subjects after 18 min of HOI in water temperatures of 35,30, and 25 degrees C. Water temperature had no significant affect on VO2 max, although HR was 8 b- min-1 lower in 30 degrees C and 15 b - min-1 lower in 25 degrees C as compared to 35 degrees C water. The results show that VO2 max was not significantly changed by HOI, scuba breathing, or brief exposures to 25, 30, and 35 degrees C water, despite significant reductions that occurred for VE and HR.     

Blood-gas measurements adjusted for temperature at three sites during incremental exercise in the horse

Rectal temperature (Tre) is often used to adjust measurements of blood gases, but these adjusted measurements may not approximate temperatures during intense exercise at main sites of gas exchange: muscle and lung. To evaluate differences in blood gases between sites, temperatures (T) were measured with thermocouples in the rectum (re), in mixed venous blood (v), in gluteal muscle (mu), and on the skin (sk) in seven Arabian horses as they underwent an incremental exercise test on a treadmill. Blood samples were drawn from the carotid artery and pulmonary artery (mixed venous) 30 s before each increase in speed and during recovery. Blood gases and pH were measured at 37 degreesC, and all variables were adjusted to Tre, Tv, and Tmu. Adjusted variables during exercise and recovery were significantly different from each other at the three sites. Linear and polynomial equations described the time course of venous temperature and from Tre and Tsk during exercise and from Tsk during recovery. Interpretation of changes in muscle metabolism and gas exchanges based on blood-gas measurements is improved if they are adjusted appropriately to Tmu or Tv, which may be predicted from Tsk in addition to Tre during strenuous exercise and from Tsk during recovery.     

Ratings of perceived exertion (RPE) during cycling exercises at constant power output

The purpose of the present investigation was to study the overall rating of perceived exertion (RPEov) according to the 6-20 scale proposed by Borg (1970) and muscular RPE (RPEmu) in exercises at constant load. The relationship between RPE and heart rate for three different loads was studied during exhausting exercises in 10 participants. Whether the drift of RPE during a 20 min exercise at constant load could be an index of the endurance time during long-lasting exercises at constant load was also investigated. At 1-week intervals, the participants performed cycling exercises up to exhaustion at 60, 73, and 86% maximal aerobic power (MAP) measured during an incremental test. Heart rate, RPEov, RPEmu and exhaustion time (tlim) were measured. The upward shift of the HRmax-RPE regressions was significant between 86, 73 and 60% MAP (p < 0.001) for RPEov and RPEmu. This result suggests that the equation HR = 10 x RPE proposed by Borg (1973) for incremental exercise is not valid for long-lasting exercise at constant load until exhaustion because the heart rate corresponding to a given RPE depends on load and time. Mean RPE increased linearly with time up to exhaustion. Unexpectedly, the relationships between RPEmu or RPEov and percentage of exhaustion time were similar for exercises at 60 and 73% MAP although the exhaustion times were very different (79.40 +/- 30.64 min versus 36.19 +/- 15.99 min, respectively) (p < 0.001). Consequently, it is likely that RPE was a subjective estimation of the hardness of exercise rather than the intensity of exercise. The RPE pattern at the beginning of long-lasting exercises at constant load (60 and 73% MAP) cannot be considered as a sensitive predictor of the point of self-imposed exhaustion for individuals. Indeed, the errors in the estimation of exhaustion time from extrapolation of RPE at the beginning of exercise were very large. Moreover, at 60% MAP, a steady-state in RPE was observed during 20 min in five subjects whose tlim were not longer than tlim of the other subjects. In addition, the data of the present study indicate that RPEmu could be more useful than RPEov in cycling.     

Thermal drive contributes to hyperventilation during exercise in sheep

The etiology of exercise hypocapnia is unknown. The contributions of exercise intensity (ExInt), lactic acid, environmental temperature, rectal temperature (Tre), and physical conditioning to the variance in arterial CO2 tension (PaCO2) in the exercising sheep were quantified. We hypothesized that thermal drive contributes to hyperventilation. Four unshorn sheep were exercised at approximately 30, 50, and 70% of maximal O2 consumption for 30 min, or until exhaustion, both before and after 5 wk of physical conditioning. In addition, two of the sheep were shorn and exercised at each intensity in a cold (<15 degrees C) environment. Tre and O2 consumption were measured continuously. Lactic acid and PaCO2 were measured at 5- to 10-min intervals. Data were analyzed by multiple regression on PaCO2. During exercise, Tre rose and PaCO2 fell, except at the lowest ExInt in the cold environment. Tre explained 77% of the variance in PaCO2, and ExInt explained 5%. All other variables were insignificant. We conclude that, in sheep, thermal drive contributes to hyperventilation during exercise.     

Differential expression of CD14, CD36 and the LDL receptor on human monocyte-derived macrophages. A novel cell culture system to study macrophage differentiation and heterogeneity

Multiple heterogeneous groups of subjects (both sexes and a wide range of maximal oxygen uptake VO2max, body mass, body surface area (AD),% body fat, and AD/mass coefficient) exercised on a cycle ergometer at a relative (%VO2max, REL) or an absolute (60 W) exercise intensity in a cool (CO 21 degrees C, 50% relative humidity), warm humid (WH 35 degrees C, 80%) and a hot dry (HD 45 degrees C, 20%) environment. Rectal temperature (Tre) responses were analysed for the influence of the individual's characteristics, environment and exercise intensity. Exposures consisted of 30-min rest, followed by 60-min exercise. The Tre was negatively correlated with mass in all conditions. Body mass acted as a passive heat sink in all the conditions tested. While negatively correlated with VO2max and VO2max per kilogram body mass in most climates, Tre was positively correlated with VO2max and VO2max per kilogram body mass in the WH/REL condition. Thus, when evaporative heat loss was limited as in WH, the higher heat production of the fitter subjects in the REL trials determined Tre and not the greater efficiency for heat loss associated with high VO2max. Body fatness significantly affected Tre only in the CO condition, where, with low skin blood flows (measured as increases in forearm blood flow), the insulative effect of fat was pronounced. In the warmer environments, high skin blood flows offset the resistance offered by peripheral adipose tissue. Contrary to other studies, Tre was positively correlated with AD/mass coefficient for all conditions tested. For both exercise types used, being big (a high heat loss area and heat capacity) was apparently more beneficial from a heat strain standpoint than having a favourable AD/mass coefficient (high in small subjects). The total amount of variance in Tre responses which could be attributed to individual characteristics was dependent on the climate and the type of exercise. Though substantial for absolute exercise intensities (52%-58%) the variance explained in Tre differed markedly for relative intensities: 72% for the WH climate with its limited evaporative capacity, and only 10%-26% for the HD and CO climates. The results showed that individual characteristics play a significant role in determining the responses of body core temperature in all conditions tested, but their contribution was low for relative exercise intensities when evaporative heat loss was not restricted. This study demonstrated that effects of individual characteristics on human responses to heat stress cannot be interpreted without taking into consideration both the heat transfer properties of the environment and the metabolic heat production resulting from the exercise type and intensity chosen. Their impact varies substantially among conditions.     

Relationship between nitric oxide and prostaglandins in carrageenin pleurisy

PURPOSE: To examine the effects of repeated bouts of exercise on the blood lactate [HLa]-ratings of perceived exertion (RPE) relation. METHODS: Six moderately trained males were studied on two occasions: a sequential exercise bouts day (SEB: 1000 h, 1130 h, and 1300 h) and a delayed exercise bouts day (DEB: 1000 h, 1400 h, and 1800 h). Each of the three exercise bouts within a given condition were 30 min in duration at the power output (PO) associated with 70% of VO2peak on a cycle ergometer. A standardized meal was provided at 0600 h. VO2, PO, HR, and RER were recorded every min during exercise and blood [HLa] and RPE were measured every 5 min during exercise. RESULTS: A 2 x 3 analysis of variance with repeated measures revealed that blood [HLa] decreased significantly with each repeated exercise bout (X +/- SEM: bout 1: SEB = 3.5 (0.3), DEB = 3.8 (0.4); bout 2: SEB = 2.6 (0.3), DEB = 2.8 (0.3); bout 3: SEB = 2.0 (0.2), DEB = 2.1 (0.4); mM). No differences were observed in the blood [HLa] response to repeated bouts of exercise between SEB and DEB. RPE-peripheral (legs, RPE-L) was higher during bout 3 compared with bout 1 (P <0.05) (bout 1: SEB = 11.8 (0.8), DEB = 12.3 (0.2); bout 2: SEB = 12.3 (0.5), DEB = 13.3 (0.4); bout 3: SEB = 13.5 (0.8), DEB = 14.0 (0.7); RPE-central (chest and breathing, RPE-C) was not affected by repeated bouts of exercise, whereas RPE-Overall (RPE-O) was higher during bout 3 compared with bouts 1 and 2 (P < 0.05) (bout 1: SEB = 12.5 (0.2), DEB = 12.3 (0.4); bout 2: SEB = 12.8 (0.4), DEB = 12.7 (0.4); bout 3: SEB = 13.7 (0.7), DEB = 13.2 (0.3)). No interaction for RPE x condition was observed. HR increased with repeated bouts of exercise with HR during exercise bout 3 being higher than HR during exercise bout 1 (164 vs. 156 bpm, P < 0.05). There was also a strong trend for HR during exercise bout 3 to be higher than HR during exercise bout 2 (P < 0.06). A trend for a reduction in VO2 with repeated exercise was observed (P < 0.07), with the reduction apparently related to the SEB condition (P < 0.12 for VO2 x condition). PO and kcal.min-1 were not affected by repeated bouts of exercise. RER decreased significantly with each repeated bout of exercise (from RER = 0.96 to RER = 0.89, P < 0.05) with no difference observed between SEB and DEB. CONCLUSIONS: We conclude that the blood [HLa]-RPE relation is altered by repeated bouts of exercise and that this alteration does not appear to be affected by recovery time between exercise bouts (up to 3.5 h of recovery). These data suggest that, after the first exercise bout, RPE should not be used to produce a specific blood [HLa] on subsequent exercise bouts.     

Thermoregulatory effects of caffeine ingestion during submaximal exercise in men

BACKGROUND: The exclusive effect of caffeine ingestion on exercise thermoregulation is unclear; data indicate that caffeine may have a positive effect, a negative effect, or no effect. METHODS: Rectal (TRE) and mean skin (TSK) temperatures, skin heat conductance (HSK), and sweat rate (MSW) were measured during 30 min of rest and subsequent 70 min of submaximal cycle-ergometer exercise (67% VO2PEAK) in 11 aerobically conditioned men (mean +/- SD 29 +/- 6 yr, 49 +/- 6 mL x min(-1) x kg(-1) VO2PEAK) under two conditions: a caffeine (10 mg x kg(-1) ingestion (CI) session and a noncaffeine ingestion (NCI) control session. RESULTS: There were no significant differences in physiological or thermoregulatory parameters during exercise: X (+/-SE) end exercise levels for the NCI and CI sessions, respectively, were VO2 = 2.50 +/- 0.09 vs. 2.55 +/- 0.09 L x min(-1); heart rate = 145 +/- 7 vs. 145 +/- 5 bpm; HSK = 30 +/- 3 vs. 28 +/- 3 kcal x m(-2) x h(-1) x degrees C(-1); MSW = 393 +/- 35 vs. 378 +/- 36 g x m(-2) x h(-1); and TRE = 38.3 +/- 0.2 vs. 38.4 +/- 0.1 degrees C. Control TSK was lower than that for CI by 0.4 to 0.5 degrees C at rest and during exercise. CONCLUSION: Ingestion of a high level (10 mg x kg(-1) of caffeine has no effect on skin heat conductance, sweating, or the rate of increase and final level of rectal temperature during moderate, submaximal leg exercise.     

Striatal dopamine dynamics are altered following an intranigral infusion of iron in adult rats

Exercise has a noted effect on skin blood flow and temperature. We aimed to characterize the normal skin temperature response to exercise by thermographic imaging. A study was conducted on ten healthy and active subjects (age=25.8+/-0.7 years) who were exposed to graded exercise for determination of maximal oxygen consumption (VO2 max), and subsequently to constant loads corresponding to 50%, 70%, and 90% of VO2 max. The skin temperature response during 20 min of constant load exercise is characterized by an initial descending limb, an ascending limb and a quasi-steady-state period. For 50% VO2 max, the temperature decrease rate was - 0.0075+/-0.001 degrees C/s during a time interval of 390+/-47 s and the temperature increase rate was 0.0055+/-0.0031 degrees C/s during a time interval of 484+/-99 s. The level of load did not influence the temperature decrease and increase rates. In contrast, during graded load exercise, a continuous temperature decrease of -0.0049+/-0.0032 degrees C/s was observed throughout the test. In summary, the thermographic skin response to exercise is characterized by a specific pattern which reflects the dynamic balance between hemodynamic and thermoregulatory processes.     

Exercise and extracorporeal blood cooling during hemodialysis

Intradialytic exercise may improve hemodialysis efficiency. Because exercise interferes with thermal energy and fluid balance, relative blood volume changes (deltaBV%), arterial blood temperatures (T(art)), mean arterial blood pressures, and heart rates (HR) were measured using different dialysate temperatures (Tdia). Four stable patients (age, 49.9 +/- 7.7 years) were studied during 22 treatments that either maintained Tdia at 35.9 degrees C +/- 0.1 degrees C (standard) or provided maximum extracorporeal cooling (cool, Tdia = 34.8 degrees C +/- 0.8 degrees C) in attempts to maintain a constant T(art). Patients exercised for 1 hr at a resistance of 21 +/- 5 W on a stationary bicycle ergometer. Energy expenditure monitored by indirect calorimetry increased from 117 +/- 38 W (baseline) to 338 +/- 116 W (exercise). Mean arterial blood pressures increased by 7 +/- 7 mmHg with cool Tdia, but remained unchanged (-1 +/- 4 mmHg) with standard Tdia (p < 0.05). However, the increase in T(art) was smaller with cool (0.1 degrees C +/- 0.3 degrees C) than with standard (0.3 degrees C +/- 0.2 degrees C) Tdia (p < 0.05). The larger increase in O2 uptake per change in HR (68 +/- 56 vs 38 +/- 17 ml/beat) indicated an increase in stroke volume when cool dialysate was used (p = NS). Exercise produced a small (0.95% +/- 0.95%), but significant, decrease in deltaBV% that reversed at the end of exercise. Intradialytic exercise was well tolerated, especially when Tdia was lowered such that hemodynamic stress to dissipate excess heat through the cutaneous circulation was reduced and blood pressure stability was improved.     

Post-exercise changes in blood pressure, heart rate and rate pressure product at different exercise intensities in normotensive humans

To evaluate the effect of exercise intensity on post-exercise cardiovascular responses, 12 young normotensive subjects performed in a randomized order three cycle ergometer exercise bouts of 45 min at 30, 50 and 80% of VO2peak, and 12 subjects rested for 45 min in a non-exercise control trial. Blood pressure (BP) and heart rate (HR) were measured for 20 min prior to exercise (baseline) and at intervals of 5 to 30 (R5-30), 35 to 60 (R35-60) and 65 to 90 (R65-90) min after exercise. Systolic, mean, and diastolic BP after exercise were significantly lower than baseline, and there was no difference between the three exercise intensities. After exercise at 30% of VO2peak, HR was significantly decreased at R35-60 and R65-90. In contrast, after exercise at 50 and 80% of VO2peak, HR was significantly increased at R5-30 and R35-60, respectively. Exercise at 30% of VO2peak significantly decreased rate pressure (RP) product (RP = HR x systolic BP) during the entire recovery period (baseline = 7930 +/- 314 vs R5-30 = 7150 +/- 326, R35-60 = 6794 +/- 349, and R65-90 = 6628 +/- 311, P < 0.05), while exercise at 50% of VO2peak caused no change, and exercise at 80% of VO2peak produced a significant increase at R5-30 (7468 +/- 267 vs 9818 +/- 366, P < 0.05) and no change at R35-60 or R65-90. Cardiovascular responses were not altered during the control trial. In conclusion, varying exercise intensity from 30 to 80% of VO2peak in young normotensive humans did not influence the magnitude of post-exercise hypotension. However, in contrast to exercise at 50 and 80% of VO2peak, exercise at 30% of VO2peak decreased post-exercise HR and RP.     

Thermogenesis during rest and exercise in cold air

Nine non-cold-acclimated subjects (5 female, 4 male, mean age 22.5 years) were studied to determine whether nonshivering thermogenesis contributes to cold-induced metabolic heat production during rest (50 min standing) and exercise (40 min treadmill walking) in 5 degrees C. Propranolol was administered orally (females, 60 mg, 1.12 mg.kg-1; males, 80 mg, 0.96 mg.kg-1) to block nonshivering thermogenesis. Measurements were taken at both 25 degrees C, 13.1 Torr (water vapor pressure; 1 Torr = 133.3 Pa) and 5 degrees C, 3.6 Torr, with sessions randomly assigned to be drug-neutral (DN), drug-cold (DC), placebo-neutral (PN), and placebo-cold (PC). Body core temperature was not different between any of the experimental conditions. Mean body temperature (5 degrees C, 32.2 +/- 0.20 degrees C (+/- SEM); 25 degrees C, 35.3 +/- 0.20 degrees C) and mean skin temperature (5 degrees C, 22.4 +/- 0.70 degrees C; 25 degrees C, 31.4 +/- 0.60 degrees C) were lower (p < 0.05) in the 5 degrees C than 25 degrees C environment (rest, exercise, drug (D), placebo (P), combined); while shivering (EMG) was higher (16.5 +/- 3.9% above baseline) at 5 degrees C than 25 degrees C (15 +/- 2.1% below baseline) (p < 0.05). The greater VO2 in 5 degrees C compared with 25 degrees C for the same condition is the thermoregulatory VO2 (TVO2). TVO2 (mL.min-1) was lower (p < 0.05) on the D (mean = 189.5 +/- 17.7) than on the P (mean = 238.1 +/- 20.2) during rest and during exercise (D, 206.1 +/- 63.7; P, 338.4 +/- 46.7). The EMG was 21% above baseline in the DC, and 12% above baseline for PC (p > 0.05). These results suggest a nonshivering component to heat production during acute cold exposure, which can be blocked with propranolol.     

Stability, controllability and observability of arterial circulation

Six subjects exercised on a bicycle ergometer at 60-70% of maximal aerobic power in a 25 degrees C ambient. Experiments on each subject were conducted at night (4:00-5:30 A.M.) and in daytime (noon-4:30 P.M.). Chest sweating rate (msw) was measured with resistance hygrometry. Forearm blood flow (BF), with an arm skin temperature of 35.5 +/- 1.2 degrees C (SD), was measured with electrocapacitance plethysmography. Esophageal temperature (Tes) was measured with a thermocouple at the level of the left atrium, and mean skin temperature (Tsk) was calculated from a weighted average of temperatures at three sites. Tes was corrected to a skin temperature of 33 degrees C as follows: T'es = Tes + (Tsk - 33 degrees C)/8. This correction reflects the relative contributions of Tes and Tsk to control of msw:T'es and BF:T'es relations were not consistently changed. In any given subject, thresholds for sweating and vasodilation were shifted about equally. These shifts averaged 0.57 degrees C (range: 0.23-0.93 degrees C)for msw and 0.63 degrees C (range: 0.17-0.98 degrees C) for BF.     

Human acclimation to work in warm and humid environments

The aim of this study was to analyse the acclimation of male Europeans during a forty-one day stay in the hot and humid climate of Thailand. We also tried to examine the phases of acclimation which would eventually be used by trainers in the elaboration of the schedule of athletes' preparation to participate in competitions in a tropical climate. Twelve Polish male subjects ageing 21-38 years participated in these examinations. In Poland and Thailand the cycloergometric exercise test with the load of 53% of VO2max was performed until a 1.2 degrees C (delta Tre) increase in rectal temperature was reached. The exercise test was executed in the same environmental conditions (i.e. 30 +/- 1 degrees C and 70 +/- 3% of relative humidity). The duration of this exercise test (DE) was used as a criterion for the efficiency of thermoregulatory functions. During acclimation, three peaks of greater exercise thermoregulatory efficiency have been found, i.e. on the 4th-5th, 11th-12th and 29th-30th days of stay. These findings are particularly important for professional athletes who wish to prepare themselves for competitions held in hot and humid climates.