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1.
Yukitoshi Aoyagi Tom M. McLellan Roy J. Shephard 《European journal of applied physiology》1995,71(2-3):187-196
This study investigated the influence of 6 versus 12 days of heat acclimation on the tolerance of low-intensity exercise in the heat while wearing protective clothing. Sixteen young men were acclimated by treadmill walking (50% of each subject's maximal aerobic power for 60 min -day-') in a climatic chamber [40°C dry bulb (db), 30% relative humidity] for either 6 consecutive days or two 6-day periods, separated by a 1-day rest. Before and after heat acclimation, the subjects performed a heat-exercise test (1.34m·s–1, 0% grade; 40°C db, 30% relative humidity), either under control conditions [wearing normal light combat clothing (continuous exercise;n = 5)] or when wearing protective clothing resistant against nuclear, biological, and chemical (NBC) agents (repeated bouts of 15-min walk + 15-min rest;n = 8). Criteria for halting the test exercise were a rectal temperature (T
re) of 39.3°C, a heart rate (f
c) 95% of the subject's observed maximum, unwillingness of the subject to continue, or the elapse of 150 min. Heat acclimation decreased overall test values ofT
re,f
c, and mean skin temperature for both control and protective clothing conditions. When wearing normal combat clothing, acclimation responses were about twice as large after 12 than after 6 days, but the response was not increased by longer acclimation when wearing NBC protective clothing. Both 6 and 12 days of acclimation increased tolerance times in NBC protective clothing by about 15 min [from 97 (4) to 112 (6) min and from 108 (10) to 120 (10) min for 6 and 12 days, respectively]. We conclude that the physiological strain and limitation of heat-exercise tolerance imposed by wearing NBC protective clothing are not reduced if heat acclimation is prolonged from 6 to 12 days. 相似文献
2.
Yukitoshi Aoyagi Tom M. McLellan Roy J. Shephard 《European journal of applied physiology》1995,71(2-3):197-206
Two methods of estimating body heat storage were compared under differing conditions of clothing, training, and acclimation to heat. Six male subjects underwent 8 weeks of physical training [60–80% of maximal aerobic power (
) for 30–45 min · day–, 3–4 days · week–1 at < 25 °C dry bulb (db)] followed by 6 consecutive days of heat acclimation (45–55%
for 60 min · day–1 at 40°C db, 30% relative humidity)]. Nine other male subjects underwent corresponding periods of control observation followed by heat acclimation. Before and after each treatment, subjects walked continuously on a treadmill (1.34 m · s–1, 2% grade) in a climatic chamber (40°C db, 30% relative humidity) for an average of 118 min (range 92–120 min) when wearing normal light combat clothing and for an average of 50 min (range 32–68 min) when wearing protective clothing resistant to nuclear, biological, and chemical agents. The heat storage was determined calorimetrically (by the balance of heat gains and losses) and thermometrically [by the conventional equations, using one or two set(s) of relative weightings for the rectal temperature (T
re) to mean skin temperature
sk of 4:1 and 4:1, 2:1 and 4:1, or 2:1 and 9:1 in thermoneutral and hot environments, respectively].
sk was calculated from 12-site measurements, weighted according to the regional distribution of body surface area and the first eigenvectors of principal component analysis. There were only minor differences (< 5%) between the heat storage values calculated by given weighting factors forT
re and
sk, whether the individual coefficients were derived from estimates of regional surface area or principal component methodologies. When wearing normal clothing, no significant differences were found between the two estimates of heat storage (calorimetry vs thermometry with an invariant relative weighting of 4:1) in any experimental condition, with one specific exception: when wearing protective clothing, thermometry underestimated the heat storage by 24–31%. This underestimation was attenuated by using two sets of relative weightings of 2: 1 and 4: 1 or 2: 1 and 9: 1. The results suggest that when subjects wearing protective clothing are transferred from thermoneutral to hot environments, the accuracy of thermometric estimates of heat storage can be improved by using two sets of weighting factors forT
re and
sk 相似文献
3.
Yukitoshi Aoyagi Tom M. McLellan Roy J. Shephard 《European journal of applied physiology》1996,73(3-4):287-298
Body heat storage can be estimated by calorimetry (from heat gains and losses) or by thermometry [from changes (Δ) in mean
body temperature (T
b) calculated as a weighted combination of rectal (T
re) and mean skin temperatures (T
sk)]. If an invariant weighting factor ofT
re andT
sk were to be used (for instance, ΔT
b = 0.8 · ΔT
re + 0.2 · ΔT
sk under hot conditions), body heat storage could be over- or underestimated substantially relative to calorimetry, depending
on whether the subject was wearing light or protective clothing. This study investigated whether discrepancies between calorimetry
and thermometry arise from methodological errors in the calorimetric estimate of heat storage, from inappropriate weightings
in the thermometric estimate, or from both. Residuals of calorimetry versus thermometric estimates were plotted against individual
variables in the standard heat balance equation, applying various weighting factors toT
re andT
sk. Whether light or protective clothing was worn, the calorimetric approach generally gave appropriate estimates of heat exchange
components and thus heat storage. One exception was in estimating latent heat loss from sweat evaporation. If sweat evaporation
exceeded 650 g·h−1 when wearing normal clothing, evaporative heat loss was overestimated and thus body heat storage was underestimated. Nevertheless,
if data beyond this ceiling were excluded from the analyses, the standard 4:1 weighting matched calorimetric heat storage
estimates quite well. When wearing protective clothing, the same 4:1 weighting approximated calorimetric heat storage with
errors of less than approximately 10%, but only if environmental conditions allowed a subject to exercise for more than 90
min. The best thermometric estimates of heat storage were provided by using two sets of relative weightings, based upon the
individual's metabolic heat production (
in kilojoules per metre squared per hour): {4 − [(
)·
] 2}:1 for an initial, thermoneutral environment and {4 + [(
) ·
] · 5}: 1 for a final, hot environment; the optimal value of
lay between 450 and 500 kJ m−2 · h−1. We concluded that the accuracy of thermometric estimates of heat storage can be improved by modifying weighting factors
ofT
re andT
sk according to the environment, type of clothing, and metabolic rate. 相似文献
4.
W. Larry Kenney 《European journal of applied physiology》1988,57(1):120-125
Summary Well matched unacclimatised older (age 55–68, 4 women, 2 men) and younger (age 19–30, 4 women, 2 men) subjects performed 75 min cycle exercise (40%
) in a hot environment (37°C, 60% rh). Rectal temperature (T
re), mean skin temperature (¯T
sk), arm blood flow (ABF, strain gauge plethysmography), and cardiac output (Q, CO2 rebreathing) were measured to examine age-related differences in heat-induced vasodilatation.T
re and¯T
sk rose to the same extent in each group during the exposure. There was no significant intergroup difference in sweat rate (older: 332±43 ml · m–2 · h–1, younger: 435±49 ml · m–2 · h–1; mean±SEM). However, the older subjects responded to exercise in the heat with a lower ABF response which could be attributed to a lower
for the same exercise intensity. The slope of the ABF-T
re relationship was attenuated in the older subjects (9.3±1.3 vs 17.9±3.3 ml · 100 ml–1 · min–1 · °C–1,p <0.05), but theT
re threshold for vasodilatation was about 37.0°C for both groups. These results suggest an altered control of skin vasodilatation during exercise in the heat in older individuals. This attenuated ABF response appears to be unrelated to
, and may reflect an age-related change in thermoregulatory cardiovascular function. 相似文献
5.
G. Havenith V. G. M. Luttikholt T. G. M. Vrijkotte 《European journal of applied physiology》1995,70(3):270-279
The present study was designed to determine the relative importance of individual characteristics such as maximal oxygen uptake (
O2max), adiposity, DuBois body surface area (A
D), surface to mass ratio (A
D: mass) and body mass, for the individual's reaction to humid heat stress. For this purpose 27 subjects (19 men, 8 women), with heterogeneous characteristics (
O2max 1.86–5.28 1 · min–1; fat% 8.0%–31.9%; mass 49.8–102.1 kg; A
D 1.52–2.33 m2) first rested (30 min) and then exercised (60 W for 1 h) on a cycle ergometer in a warm humid climate (35°C, 80% relative humidity). Their physiological responses at the end of exercise were analysed to assess their relationship with individual characteristics using a stepwise multiple regression technique. Dependent variables (with ranges) included final values of rectal temperature (T
re 37.5–39.0°C), mean skin temperature (T
sk 35.7–37.5°C), body heat storage (S 3.2–8.1 J · g–1), heart rate (HR 100–172 beat · min–1), sweat loss (397–1403g), mean arterial blood pressure (BPa, 68–96 mmHg), forearm blood flow (FBF, 10.1–33.9 ml · 100ml–1 · min–1) and forearm vascular conductance (FVC = FBF/BPa, 0.11–0.49 ml · 100 ml–1 · min–1 · mmHg–1). The T
re, T
sk and S were (34%–65%) determined in the: main by (
O2max), or by exercise intensity expressed as a percent age of
O2max (%
O2max). For T
re, A
D: mass ratio also contributed to the variance explained, with about half the effect of (
O2max), For T
sk, fat% contributed to the variance explained with about two-third the effect of
O2max. Total body sweat loss was highly dependent (50%) on body size (A
D or mass) with regular activity level having a quarter of the effect of body size on sweat loss. The HR, similar to T
re, was determined by
O2max (48%–51%), with less than half the effect of A
D or A
D :mass (20%). Other circulatory parameters (FBF, BPa, FVC) showed little relationship with individual characteristics ( < 36% of variance explained). In general, the higher the (
O2max), and/or the bigger the subject, the lower the heat strain observed. The widely accepted concept, that body core temperature is determined by exercise intensity expressed as %
O2max and sweat loss by absolute heat load, was only partially supported by the results. For both variables, other individual characteristics were also shown to contribute. 相似文献
6.
Tom M. McLellan Ingrid F. Smith Greg A. Gannon Jiri Zamecnik 《European journal of applied physiology》2000,83(4-5):336-343
This study examined whether a 5 mg dose of melatonin induced a lower rectal temperature (T
re) response at rest in both a cool and hot environment while wearing normal military combat clothing, and then examined the
influence of this response on tolerance to exercise in the heat while wearing protective clothing. Nine men performed four
randomly ordered trials involving 2 h of rest at ambient temperatures of either 23 °C or 40 °C followed by exercise at an
ambient temperature of 40 °C. The double-blind ingestion of placebo or melatonin occurred after 30 min of rest. The mean T
re during rest at 23 °C had decreased significantly from 36.8 (SD 0.1) °C to 36.7 (SD 0.2) °C at 90 min following the ingestion
of the drug, whereas values during the placebo trial did not change. The lower T
re response during the melatonin trial remained during the first 50 min of exercise in the heat while wearing the protective
clothing. Since the final mean T
re at the end of exercise also was significantly reduced for the melatonin [39.0 (SD 0.4) °C] compared with the placebo [mean
39.1 (SD 0.3) °C] trial, tolerance times approximated 95 min in both conditions. During rest at 40 °C, melatonin did not affect
the mean T
re response which increased significantly during the last 90 min from 36.9 (SD 0.1) °C to 37.3 (SD 0.1) °C. This increase in
T
re during the rest period prior to donning the protective clothing decreased tolerance time approximately 30 min compared with
the trials that had involved rest at 23 °C. Total heat storage summated over the rest and exercise periods was not different
among the trials at 15 kJ · kg−1. It was concluded that the small decrease in T
re following the ingestion of 5 mg of melatonin at rest in a cool environment had no influence on subsequent tolerance during
uncompensable heat stress.
Accepted: 26 June 2000 相似文献
7.
Summary Metabolic heat production (M), clothing heat transfer characteristics, and the environment dictate a required evaporative cooling (Ereq) from the body to maintain thermal balance. However, the maximal evaporative capacity (Emax) is dictated by vapor transfer properties of the clothing and environment. Relationships between metabolic load, environmental conditions, clothing and sweat loss were studied in 34 heat-acclimatized males categorized into four groups (eight, eight, eight, and ten subjects) and exposed to various environmental conditions (ambient temperature, 20–54 C, and relative humidity, 10–90%), three levels of metabolic rate (resting; walking 1.34 m·s–1, level; or walking 1.34 m·s–1, 5% grade) while wearing various clothing ensembles (shorts and T-shirts, fatigues, fatigues plus overgarment, or sweat suit). Individual groups were not exposed to all combinations. Exposures lasted 120 min: either 10 min rest — 50 min exercise — 10 min rest — 50 min exercise, or 120 min at rest. Physiological measurements included heart rate, rectal temperature, mean skin temperature, energy expenditure and sweat loss (msw). Emax and Ereq were calculated from environmental conditions, metabolism, clothing insulation and permeability. The ratio Ereq/msw was found to correlate with Emax and not with M. The predictive equation for sweat loss was: msw=18.7×Ereq×(Emax)–0.455 within the limits 50req<360; W·m–2 and 20max<525; W·m–2. This formula predicts sweat loss for specific work loads, climates and clothing ensembles. 相似文献
8.
Lawrence E. Armstrong Roger W. Hubbard Elaine L. Christensen Jane P. De Luca 《European journal of applied physiology》1990,60(3):202-208
Summary It has been reported that scores from a temperate-environment step test describe the heat-tolerance status of prior heatstroke patients (HP). This investigation evaluated the ability of this temperate-environment heat-tolerance test (HTT) to indicate altered heart rate (HR) and rectal temperature (T
re
)responses of HP, after 7 days of heat acclimation. On day 1, ten male HP (61 ± 7 days post-heatstroke) and five control subjects (C) bench-stepped (0.30 m high, 27 steps · min–1) for 15 min (25.8° C dry bulb, 16.2° C wet bulb). On days 2–8, subjects underwent heat acclimation (40.1° C dry bulb, 23.8°C wet bulb; treadmill, 90 min · day–1). Heat acclimation resulted in significant decreases in final HR (152±5 vs 130±3 beats·min–1
P<0.025) and finalT
re (38.62±0.11 vs 38.13±0.07°C,p < 0.01) in HP. One HP but no C was defined heat intolerant, exhibiting inability to adapt to daily exercise in the heat. On day 9, HP repeated HTT, exactly as performed on day 1; mean group HTT scores did not change (day 1=39±6; day 9=48±6,P>0.05). All physical characteristics and physiological responses of HP (days 1, 2, 7, 9) were statistically similar (P>0.05) to those of C. In contrast to heat-acclimation data, HTT scores (score 30) indicated that four HP were heat intolerant on day 1 and two HP were heat intolerant on day 9. It was concluded that HTT was not a substitute for lengthier tests of heat tolerance conducted in hot environments, because HTT scores (at 25.8°C did not reflect HR andT
re
responses (at 40.1° C) in 33% of heat-acclimated (e.g., heat-tolerant) HP. In addition, HTT scores did not validly discriminate between heat tolerant and heat-intolerant HP. 相似文献
9.
Kazuyo Tsuzuki-Hayakawa Yutaka Tochihara Tadakatsu Ohnaka 《European journal of applied physiology》1995,72(1-2):12-17
The study was conducted to investigate the thermoregulation of young children compared to that of adults. A group of 19 children (ages 9 months-4.5 years), with only 3 children aged 3 years or above, and 16 adults first rested in a thermoneutral room (air temperature 25°C relative humidity 50%, air velocity 0.2 m·s–1). They were then exposed to a hot room (air temperature 35°C, relative humidity 70%, air velocity 0.3 m·s–) next door for 30 min, and then returned to the thermoneutral room where they stayed for a further 30 min. The rectal temperature (T
re), skin temperatures (T
sk) at seven sites, heart rate (HR), total sweat rate (
), local sweat rate (
) and the Na+ concentration of the sweat were measured. There was no significant difference inT
re between the children and their mothers in the rest phase. However, theT
re of the children increased as soon as they entered the hot room and was significantly higher than during the control period, and than that of the mothers during heat exposure. MeanT
sk, forehead, abdomen and instepT
sk were significantly higher in the children during both the thermoneutral and heat exposure. The
was significantly higher and Na+ concentrations in the sweat on the back and upperarm were significantly lower for the children during the heat exposure. They had a greater body surface area-to-mass ratio than the mothers by 64%, which indicated that they had advantages for thermal regulation. However, the sweating andT
sk responses of the children were not enough to prevent a rise in body temperature. These results would suggest that the young children had the disadvantage of heating up easily due to their smaller body sizes and there may be maturation-related differences in thermoregulation during the heat exposure between young children and mothers. 相似文献
10.
B. L. Bennett R. D. Hagan K. A. Huey C. Minson D. Cain 《European journal of applied physiology》1995,70(4):322-328
This study evaluated the effectiveness of a six-pack versus a four-pack cool vest in reducing heat strain in men dressed in firefighting ensemble, while resting and exercising in a warm/humid environment [34.4°C (day bulb), 28.9°C (wet bulb)]. Male volunteers (n = 12) were monitored for rectal temperature (T
re), mean skin temperature (T
sk), heart rate, and energy expenditure during three test trials: control (no cool vest), four-pack vest, and six-pack vest. The cool vests were worn under the firefighting ensemble and over Navy dungarees. The protocol consisted of two cycles of 30 min seated rest and 30 min walking on a motorized treadmill (1.12 m · s–1, 0% grade). Tolerance time for the control trial (93 min) was significantly less than both vest trials (120 min). Throughout heat exposure, energy expenditure varied during rest and exercise, but no differences existed among all trials (P > 0.05). During the first 60 min of heat exposure, physiological responses were similar for the four-pack and six-pack vests. However, during the second 60 min of heat exposure the six-pack vest had a greater impact on reducing heat strain than the four-pack vest. PeakT
e andT
sk at the end of heat exposure for 6-pack vest [mean (SD) 38.0(0.3)°C and 36.8(0.7)°C] were significantly lower compared to four-pack [38.6 (0.4)°C and 38.1(0.5)°C] and controls [38.9(0.5)°C and 38.4(0.5)°C]. Our findings suggest that the six-pack vest is more effective than the four-pack vest at reducing heat strain and improves performance of personnel wearing a firefighting ensemble. 相似文献
11.
Y. Epstein R. Arnon D. Moran D. S. Seidman Y. Danon 《European journal of applied physiology》1990,61(1-2):128-132
Summary The effect of pyridostigmine on thermoregulatory responses was evaluated during exercise and heat stress. Eight heat acclimated, young adult male subjects received four doses of pyridostigmine (30 mg) or identical placebo tablets every 8 h, in a double blind, randomized, cross-over trial. A 30.3%, SD 4.6% inhibition of the circulating cholinesterase (ChE) activity was induced in the pyridostigmine-treated group. The subjects were exposed to 170-min exercise and heat-stress (dry bulb temperature, 33° C; relative humidity 60%) consisting of 60 min in a sitting position and two bouts of 50-min walking (1.39 m · s–1, 5% gradient) which were separated by 10-min rest periods. No differences were found between treatments in the physiological responses and heat balance parameters at the end of exposure: heart rate (f
c) was 141 beats · min–1, SD 16 and 150 beats · min–1, SD 12, rectal temperature (T
re) was 38.5°C, SD 0.4° and 38.6°C, SD 0.3°, heat storage was 60 W · m–2, SD 16 and 59 W · m–2, SD 15 and sweat rate was 678 g · h–1, SD 184 and 661 g · h–1, SD 133, in the pyridostigmine and placebo treatments, respectively. The changes in T
re and f
c over the heat-exercise period were parallel in both study and control groups. Pyridostigmine caused a slight slowing of f
c (5 beats·min–1) which was consistent throughout the entire exposure (P<0.001) but was of no clinical significance. The overall change in fc was similar for both groups. We have concluded that pyridostigmine administration, in a dose sufficient to induce a moderate degree of ChE inhibition, does not significantly affect performance of exercise in the heat. 相似文献
12.
Shigeru Katsuta Yoji Kanao Yukitoshi Aoyagi 《European journal of applied physiology》1988,58(1-2):68-73
Summary Our purpose was to test the significance of exhaustive training in aerobic or endurance capacity. The extent of adaptations to endurance training was evaluated by assessing the increase in physical performance capability and oxidative markers in the organs of rats trained by various exercise programs. Rats were trained by treadmill running 5 days · week–1 at 30 m · min–1 for 8 weeks by one of three protocols:T
1 — 60 min · day–1;T
2 — 120 min · day–1; andT
3 — 120 min · day–1 (3 days · week–1) and to exhaustion (2 days · week–1). GroupsT
2 andT
3 ran for longer thanT
1 in an endurance exercise test (P<0.05), in which the animals ran at 30 m · min–1 to exhaustion; no difference was observed between groupsT
2 andT
3. All 3 trained groups showed a similar increase (20–27%) in the fast-twitch oxidative-glycolytic (FOG) fibers with a concomitant decrease in the fast-twitch glycolytic (FG) fiber population in gastrocnemius (p<0.05). The capillary supply in gastrocnemius increased with the duration of exercise (p<0.05): no difference was found between groupsT
2 andT
3. Likewise, no distinction was seen between groupsT
2 andT
3 in the increase in succinate dehydrogenase activity in gastrocnemius and the heart. These results suggest that the maximal adaptive response to endurance training does not require daily exhaustive exercise. 相似文献
13.
C. M. Windle I. F. G. Hampton P. Hardcastle M. J. Tipton 《European journal of applied physiology》1994,68(3):194-199
Two experiments were undertaken to investigate the effects of warming the body upon the responses during a subsequent cold water immersion (CWI). In both experiments the subjects, wearing swimming costumes, undertook two 45-min CWIs in water at 15° C. In experiment 1, 12 subjects exercised on a cycle ergometer until their rectal temperatures (T
re) rose by an average of 0.73°C. They were then immediately immersed in the cold water. Before their other CWI they rested seated on a cycle ergometer (control condition). In experiment 2, 16 different subjects were immersed in a hot bath (40° C) until their T
re rose by an average of 0.9° C; they were then immediately immersed in the cold water. Before their other CWI they were immersed in thermoneutral water (35° C; control condition). Heart rate in both experiments and respiratory frequency in experiment 1 were significantly (P < 0.05) higher during the first 30 s of CWI following active warming. In experiment 1, the rate of fall of T
re during the final 15 min of CWI was significantly (P < 0.01) faster when CWI followed active warming (2.46° C · h–1) compared with the control condition (1.68°C · h–1). However, this rate was observed when absolute T
re was still above that seen in the control CWIs. It is possible, therefore, that if longer CWIs had been undertaken, the two temperature curves may have converged and thereafter fallen at similar rates; this was the case with the aural temperature (T
au) seen in experiment 1 and the T
au and T
re in experiment 2. It is concluded that pre-warming is neither beneficial nor detrimental to survival prospects during a subsequent CWI. 相似文献
14.
J. E. Greenleaf T. Hutchinson M. Shaffer-Bailey R. Looft-Wilson 《European journal of applied physiology》1996,72(4):303-309
The purpose was to investigate the mechanism for the excessive exercise hyperthermia following deconditioning (reduction of physical fitness). Rectal (T
re) and mean skin (
) temperatures and thermoregulatory responses were measured in six men [mean (SD) age, 32 (6) years; mass, 78.26 (5.80) kg; surface area, 1.95 (0.11)m2; maximum oxygen uptake (
), 48 (6) ml·min–1·kg–1; whilst supine in air at dry bulb temperature 23.2 (0.6)°C, relative humidity 31.1 (11.1)% and air speed 5.6 (0.1) m·min–1] during 70 min of leg cycle exercise [51 (4)%
] in ambulatory control (AC), or following 6 h of chair rest (CR), 6° head-down bed rest (BR), and 20° (WI20) and 80° (WI80) foot-down water immersion [water temperature, 35.0 (0.1)°C]. Compared with the AC exercise T
re [mean (SD) 0.77 (0.13)°C], T
re after CR was 0.83 (0.08)°C (NS), after BR 0.92 (0.13)°C (*P<0.05), after WI80 0.96 (0.13)°C*, and after WI20 1.03 (0.09)°C*. All
responded similarly to exercise: they decreased (NS) by 0.5–0.7°C in minutes 4–8 and equilibrated at +0.1 to +0.5°C at 60–70. Skin heat conductance was not different among the five conditions (range = 147–159 kJ·m–2·h–1·°C–1). Results from an intercorrelation matrix suggested that total body sweat rate was more closely related toT
re at 70 min (T
re70) than limb sweat rate or blood flow. Only 36% of the variability inT
re70 could be accounted for by total sweating, and less than 10% from total body dehydration. It would appear that multiple factors are involved which may include change in sensitivity of thermo- and osmoreceptors. 相似文献
15.
Summary The purpose of this study was to evaluate the role of knit structure in underwear on thermoregulatory responses. Underwear manufactured from 100% polypropylene fibres in five different knit structures (1-by-1 rib, fleece, fishnet, interlock, double-layer rib) was evaluated. All five underwear prototypes were tested as part of a prototype clothing system. Measured on a thermal manikin these clothing systems had total thermal resistances of 0.243, 0.268, 0.256, 0.248 and 0.250 m2 · K · W–1, respectively (including a value for the thermal resistance of the ambient environment of 0.104 m2 · K · W–1). Human testing was done on eight male subjects and took place at ambient temperature (T
a)=5°C, dew point temperature (T
dp)=–3.5° C and air velocity (V
a)=0.32 m · s–1. The test comprised a repeated bout of 40-min cycle exercise (315 W · m–2; 52%, SD 4.9% maximal oxygen uptake) followed by 20 min of rest (62 W · m–2). The oxygen uptake, heart rate, oesophageal temperature, skin temperature,T
a,T
dp at the skin and in the ambient air, onset of sweating, evaporation rate, non-evaporated sweat accumulated in the clothing and total evaporative loss of mass were measured. Skin wettedness was calculated. The differences in knit structure of the underwear in the clothing systems resulted in significant differences in mean skin temperature, local and average skin wettedness, non-evaporated and evaporated sweat during the course of the intermittent exercise test. No differences were observed over this period in the core temperature measurements.The views, opinions and/or findings in this report are those of the authors and should not be construed as an official Department of the Army position, policy, or decision, unless so designated by other official documentation 相似文献
16.
G. Dewasmes B. Bothorel A. Hoeft V. Candas 《European journal of applied physiology》1993,66(6):542-546
Summary Thermoregulatory sweating [total body (m
sw,b), chest (m
sw,c) and thigh (m
sw,t) sweating], body temperatures [oesophageal (T
oes) and mean skin temperature (T
sk)] and heart rate were investigated in five sleep-deprived subjects (kept awake for 27 h) while exercising on a cycle (45 min at approximately 50% maximal oxygen consumption) in moderate heat (T
air andT
wall at 35° C. Them
sw,c andm
sw,t were measured under local thermal clamp (T
sk,1), set at 35.5° C. After sleep deprivation, neither the levels of body temperatures (T
oes,T
sk) nor the levels ofm
sw, b,m
sw, c orm
sw, t differed from control at rest or during exercise steady state. During the transient phase of exercise (whenT
sk andT
sk,1 were unvarying), them
sw, c andm
sw, t changes were positively correlated with those ofT
oes. The slopes of them
sw, c versusT
oes, orm
sw, t versusT
oes relationships remained unchanged between control and sleep-loss experiments. Thus the slopes of the local sweating versusT
oes, relationships (m
sw, c andm
sw, t sweating data pooled which reached 1.05 (SEM 0.14) mg·cm–2·min–1°C–1 and 1.14 (SEM 0.18) mg·cm–2·min–1·°C–1 before and after sleep deprivation) respectively did not differ. However, in our experiment, sleep deprivation significantly increased theT
oes threshold for the onset of bothm
sw, c andm
sw, t (+0.3° C,P<0.001). From our investigations it would seem that the delayed core temperature for sweating onset in sleep-deprived humans, while exercising moderately in the heat, is likely to have been due to alterations occurring at the central level. 相似文献
17.
The purpose of the present study was to investigate the influence of hypohydration and fluid replacement on tolerance to
an uncompensable heat stress. Eight healthy young males completed a matrix of six trials in an environmental chamber, set
at 40°C and 30% relative humidity, while wearing nuclear, biological, and chemical protective clothing. Subjects performed
either light (3.5 km · h−1, 0% grade, no wind) or heavy (4.8 km · h−1, 4% grade, no wind) treadmill exercise combined with three hydration states [euhydration with fluid replacement (EU/F), euhydration
without fluid replacement (EU/NF), and hypohydration with fluid replacement (H/F)]. Hypohydration of 2.2% body mass was achieved
by exercise and fluid restriction on the day preceding the trials. No differences in the endpoint mean skin temperature (Tˉsk), sweat rate, or rectal temperature (T
re) were observed among the hydration conditions for either work rate. During light exercise, the change in T
re (ΔT
re) was significantly higher with H/F than EU/F after 40 min, and heart rate was greater after 25 min. The heart rate was greater
during EU/NF than during EU/F after 60 min. Tolerance times were significantly greater for EU/F than for either EU/NF or H/F.
With heavy exercise, no differences in ΔT
re were observed across hydration conditions. Compared to EU/F, heart rates were higher after 10 and 30 min for H/F and EU/NF,
respectively. Tolerance times were significantly less during H/F than with either of the EU conditions. Stroke volume was
significantly decreased in H/F trials compared to EU/F trials for both light and heavy work rates, but no differences in cardiac
output were observed. It was concluded that even minor levels of hypohydration significantly impaired exercise tolerance in
a severely uncompensable heat stress environment at both light and heavy exercise intensities.
Accepted: 17 June 1997 相似文献
18.
Yoshio Kobayashi Yoshiro Ando Shinya Takeuchi Kazuko Takemura Noriaki Okuda Yoshiaki Isobe Shozo Takaba Kokichi Ohara 《European journal of applied physiology》1980,45(2-3):189-198
Summary Five distance runners (H group) performed a 60 min bicycle exercise at a load of 60–70% VO2 max in a moderately hot environment (T
a: 33.5 C, 60% RH). Following a period of heat acclimation with bench-stepping at a load equal to about 25–30% VO2 max, in a hot environment (T
a: 45–50 C, 30–40% RH) for 9 days, the work test was repeated. Two control subjects (R) performed the same work tests with no heat acclimation. Heat acclimation increased performance time. Rectal temperature, mean skin temperature, heart rate, and Na+ concentrations in sweat were lower in H and, with one exception, sweat rate was higher after heat acclimation. All H subjects demonstrated that the linear relationship between sweat rate and rectal temperature was shifted to a lower temperature (threshold shift). This shift correlated with a lowering of resting rectal temperature. The magnitude of the reduction in those two temperatures due to heat acclimation was identical. The observed improvement of work performance in moderate heat following heat acclimation to a higher temperature is attributed to a more efficient thermoregulatory mechanism. 相似文献
19.
A. Buguet R. Gati G. Soubiran J. P. Straboni A. M. Hanniquet G. Livecchi-Gonnot J. Bittel 《European journal of applied physiology》1988,58(3):334-339
Summary Seven volunteers (3 females and 4 males; 3 Caucasians and 4 Africans) participated in two 24 h sessions during the cool dry (CD) and the hot dry (HD) seasons of the sahelian tropical climate. Body temperatures were taken on portable cassette recorders for 24 h. Rectal (T
re) and mean skin (¯T
sk) temperatures decreased in the HD compared to the CD conditions, meeting one of the criteria for adaptation to heat. No ethnic differences in thermal responses were found. Males and females differed in their body temperature rhythms and in their reactions to heat. Body temperatures were higher in females than in males. Males reacted to heat with a decrease in T
re, without change in the T
re-¯T
sk gradient. Females showed a decrease in both T
re and ¯T
sk, more marked for ¯T
sk, with an increase in the T
re-¯T
sk gradient. It was concluded that males showed seasonal acclimatization to heat via a decrease in metabolism confirmed by a decrease in plasma levels of thyroid stimulating hormone (TSH) in the HD condition. Females showed a mixed metabolic and thermolytic type of acclimatization, with an absence of variation in plasma TSH levels. In conclusion, the steady rise in temperature between the CD and HD conditions was sufficient to trigger an acclimatization to heat similar in Caucasian and African subjects, although exposure to the external climate differed widely. 相似文献
20.
George Havenith Yoshimitsu Inoue Viktor Luttikholt W. Larry Kenney 《European journal of applied physiology》1995,70(1):88-96
Cross-section comparisons of the effect of age on physiological responses to heat stress have yielded conflicting results, in part because of the inability to separate chronological age from factors which change in concert with the biological aging process. The present study was designed to examine the relative influence of age on cardiovascular and thermoregulatory responses to low intensity cycle exercise (60 W for 1 h) in a warm humid environment (35°C, 80% relative humidity). Specifically, the relative importance of age compared to other individual characteristics [maximal oxygen uptake (
max), physical activity level, anthropometry, and adiposity] was determined by multiple regression analysis in a heterogeneous sample of 56 subjects in which age (20–73 years) and
max (1.864–44 l · min–1) were not interrelated. Dependent variables (with ranges) included final values of thermoregulatory responses [rectal temperature (T
re, 37.8–39.2°C), calculated heat storage (S, 3.4–8.1 J · g–1), sweat loss (238–847 g · m–2)] and cardiovascular responses [heart rate (HR, 94–176 beats min–1), forearm blood flow (FBF, 5.3–31.3 ml · 100 ml–1 · min–1), mean arterial blood pressure (MAP, 68–122 mmHg), and forearm vascular conductance (FVC = FBF · MAP–1, 0.06–0.44 ml · 100 ml–1 · min–1 · mmHg–1). Age had no significant influence onT
re,S, or sweat loss, all of which were closely related to
max. On the other hand, HR, MAP, FBF, and FVC were related to both age and
max. Anthropometric variables and adiposity had secondary, but statistically significant, effects on MAP, FBF, FVC, and sweat loss. With respect to exercise in a warm humid environment, it was concluded that the effect of age on body temperature and sweating was negligible compared to effects related to
max, but that chronological age had an independent effect on cardiovascular effector responses. 相似文献