A COMPARISON OF THE IMMEDIATE EFFECTS OF MODERATE EXERCISE IN THE EARLY MORNING AND LATE AFTERNOON ON CORE TEMPERATURE AND CUTANEOUS THERMOREGULATORY MECHANISMS

Twelve healthy male subjects each undertook two bouts of moderate exercise (70% VO₂max for 30 minutes) in the morning (08:00) and late afternoon (18:00) at least 4 days apart. Measurements were made of heart rate, core (rectal) temperature, sternum skin temperature, and forearm skin blood flow during baseline conditions, during the bout of exercise, and throughout a 30-minute recovery period. Comparisons were made of the changes of heart rate, temperature, and skin blood flow produced by the exercise at the two times of day. Student t tests indicated that baseline values for core temperature (37.15°C ±. 06°C vs. 36.77°C ± 0.06°C) and sternum temperature (33.60°C ± 0.29°C vs. 32.70°C ± 0.38°C) were significantly (p <. 05) higher in the late afternoon than the early morning. Two-way analysis of variance (ANOVA) indicated that the increases in core and sternum temperatures during exercise were significantly less (p =. 0039 and. 0421, respectively) during the afternoon bout of exercise compared with the morning, even though the work loads, as determined by changes in heart rate, were not significantly different (p =. 798) at the two times of testing. There were also tendencies for resting forearm skin blood flow to be higher in the afternoon than in the morning and for exercise to produce a more rapid rise in this variable in the afternoon. The possible mechanisms producing these responses to exercise are discussed in terms of those that are responsible for the normal circadian rhythm of core temperature. It is concluded that the body's ability to remove a heat load is less in the early morning, when the circadian system is in a “heat gain” mode, than in the late afternoon, when heat gain and “heat loss” modes are balanced more evenly. (Chronobiology International, 17(2), 197–207, 2000)     

A comparison of the immediate effects of moderate exercise in the late morning and late afternoon on core temperature and cutaneous thermoregulatory mechanisms

Twelve healthy male subjects each undertook two bouts of moderate exercise (70% VO2max for 30 minutes) in the morning (08:00) and late afternoon (18:00) at least 4 days apart. Measurements were made of heart rate, core (rectal) temperature, sternum skin temperature, and forearm skin blood flow during baseline conditions, during the bout of exercise, and throughout a 30-minute recovery period. Comparisons were made of the changes of heart rate, temperature, and skin blood flow produced by the exercise at the two times of day. Student t tests indicated that baseline values for core temperature (37.15 degrees C +/- 0.06 degrees C vs. 36.77 degrees C +/- 0.06 degrees C) and sternum temperature (33.60 degrees C +/- 0.29 degrees C vs. 32.70 degrees C + 0.38 degrees C) were significantly (p < .05) higher in the late afternoon than the early morning. Two-way analysis of variance (ANOVA) indicated that the increases in core and sternum temperatures during exercise were significantly less (p = .0039 and .0421, respectively) during the afternoon bout of exercise compared with the morning, even though the work loads, as determined by changes in heart rate, were not significantly different (p = .798) at the two times of testing. There were also tendencies for resting forearm skin blood flow to be higher in the afternoon than in the morning and for exercise to produce a more rapid rise in this variable in the afternoon. The possible mechanisms producing these responses to exercise are discussed in terms of those that are responsible for the normal circadian rhythm of core temperature. It is concluded that the body's ability to remove a heat load is less in the early morning, when the circadian system is in a "heat gain" mode, than in the late afternoon, when heat gain and "heat loss" modes are balanced more evenly.     

Time-of-Day Effects on Anaerobic Muscular Power in a Moderately Warm Environment

This study evaluated the influence of a neutral vs. a moderately warm environment on the diurnal variation in muscular power. Twelve male subjects [27.0 (±4) years] performed two different jump tests [a squat jump (SJ) and a counter-movement jump (CMJ)] and a brief maximal sprint on cycle ergometer (CS) in four different conditions (morning/neutral, morning/moderately warm and humid, afternoon/neutral, and afternoon/moderately warm and humid). The morning experiments were conducted between 07:00 and 09:00 h, and the afternoon experiments were conducted between 17:00 and 19:00 h. The mean laboratory temperatures and humidity were 20 (±1)°C, 70 (±5)% and 29 (±1)°C, 57 (±4)% for the neutral and moderately warm and humid conditions, respectively. Rectal temperature and leg skin temperature were significantly dependent on both time-of-day and ambient temperature. An interaction effect (P < 0.05) was noted between time-of-day and ambient temperature for the power developed for the CMJ, the SJ, and half of a pedal revolution during the cycling sprint. In summary, (i) the same subjects were influenced by time-of-day differently, depending on the ambient temperature during testing; (ii) time-of-day affected muscular performance only in the neutral condition, (iii) the moderately warm and humid condition blunted the diurnal variation in muscular performance, and (iv) the effect of the ambient temperature was dependent on time-of-day.     

Thermoregulatory responses of lower limb amputees during exercise in a hot environment

Lower limb amputees (LLAs) have less skin surface required for sweating; thus, the ability to dissipate heat from the body may decrease and the risk of heat illness may increase during exercise in a hot environment. However, no study has compared the thermoregulatory responses during exercise between LLAs and able-body (AB) individuals with different body surface areas. This study aimed to compare the thermoregulatory responses of LLAs with those of AB individuals during exercise in a hot environment. Seven LLAs (LLA group) and 7 able-body individuals (AB group) participated in the study. A 60% peak power output of arm crank upper-body exercise was performed for 60 min in a hot environment (32 °C, 50% relative humidity). There was no difference in the increase in rectal temperature (LLA: 0.8 ± 0.2 °C, AB: 0.8  ± 0.2 °C) and mean skin temperature between the groups during the 60-min exercise. In the LLA group, the accumulated local sweat rate of the thigh during exercise was significantly higher on the non-cut side than on the cut side (64.6 ± 43.0 mg/h vs. 37.0 ± 27.2 mg/h, p < 0.05). The total sweat rate was significantly higher in the LLA group than in the AB group (1.18 ± 0.37 kg/h vs. 0.84 ± 0.10 kg/h, p < 0.05). Thermal sensation and comfort were lower in the LLA group than in the AB group. Different heat loss responses were observed in the AB and LLA groups during exercise in the heat. The LLA group compensates for sweating on the cut side due to an increase in sweat loss on the intact limb, thereby preserving appropriate thermoregulation during exercise.     

Differences between sexes in thermoregulatory responses and exercise time during endurance exercise in a hot environment following pre-cooling with ice slurry ingestion

This study aimed to examine differences between sexes in thermoregulatory responses and exercise time after ice slurry ingestion in a hot environment. Twenty-four healthy adults (male n = 12, body weight (BW) = 65.8 ± 10.3; female n = 12, BW = 58.2 ± 10.0) ingested 7.5 g/kg of either ice slurry at −1 °C (ICE) or control water at 20 °C (CON) before cycling at 55%VO₂ max in a hot environment (controlled at 38 °C, 40% relative humidity). Rectal (Tre) and skin (Tsk) temperature, heart rate, sweat rate, respiratory gases, ratings of thermal sensation (TS), thermal comfort (TC), and rating of perceived exertion (RPE) were measured. Ice slurry did not improve exercise time in both sexes despite Tre was significantly lower in ICE than CON in both sexes. Tre, Tsk, HR, sweat rate and TS did not differ between sexes. TC and RPE in ICE were significantly higher during exercise in males than in females. In conclusion, there were no sex differences in the effects of pre-cooling with ice slurry ingestion; however, pre-cooling with ice slurry may be more effective in mitigating ratings of TC and RPE in females than males.     

Rectal temperature,distal sweat rate,and forearm blood flow following mild exercise at two phases of the circadian cycle

Changes in rectal temperature during mild exercise in the middle of the rising (11:00 h) and falling (23:00 h) phases of the circadian rhythm of resting core temperature have been compared. Seven healthy males were studied at rest, while exercising on a cycle ergometer (60 min at 80 W), and during the first 30 min of recovery. Rectal temperature, forearm blood flow, and forearm sweat rate were measured at 1 min intervals throughout. During exercise, there were significant time‐of‐day differences in the profiles of all three variables, and in the thresholds for increases in forearm blood flow and sweating. Forearm blood flow and sweat rate were recruited more rapidly and to a greater extent with evening exercise, and rectal temperature rose less. Analysis of covariance, with rectal temperature as the covariate, indicated the associations between it and forearm blood flow or sweating were significantly different (p<0.05) between the two times of day. There were also significant (p<0.05) time‐of‐day effects for forearm blood flow and sweating that were independent of rectal temperature. During recovery, rectal temperature fell more quickly in the late evening than late morning. Forearm blood flow and sweating also showed time‐of‐day differences, but these did not co‐vary with rectal temperature. Control of rectal temperature during exercise and recovery appears to be more effective in the late evening than late morning, and differences in forearm blood flow and sweating, as well as factors independent of these two variables, contribute to this difference. The results support our “heat‐gain/heat‐loss modes” hypothesis.     

MAXIMAL POWER,BUT NOT FATIGABILITY,IS GREATER DURING REPEATED SPRINTS PERFORMED IN THE AFTERNOON

The present study was designed to investigate if the suggested greater fatigability during repeated exercise in the afternoon, compared to the morning, represents a true time-of-day effect on fatigability or a consequence of a higher initial power. In a counterbalanced order, eight subjects performed a repeated-sprint test [10?×?(6 s of maximal cycling sprint?+?30 s of rest)] on three different occasions between: 08:00–10:00, 17:00–19:00, and 17:00-19:00?h controlled (17:00–19:00?h_cont, i.e., initial power controlled to be the same as the two first sprints of the 08:00–10:00?h trial). Power output was significantly (p?<?0.05) higher for sprints 1, 2, and 3 in the afternoon than in the morning (e.g., sprint 1: 23.3 ±1 versus 21.2 ±1 W·kg^?1), but power decrement for the 10 sprints was also higher in the afternoon. Based on the following observations, we conclude that this higher power decrement is a consequence of the higher initial power output in the afternoon. First, there was no difference in power during the final five sprints (e.g., 20.4 ±1 versus 19.7 ±1 W·kg^?1 for sprint 10 in the afternoon and morning, respectively). Second, the greater decrement in the afternoon was no longer present when participants were producing the same initial power output in the afternoon as in the morning. Third, electromyographic activity of the vastus lateralis decreased during the exercise (p?<?0.05), but without a time-of-day effect. (Author correspondence: sebastien.racinais@aspetar.com)     

Seasonal Rhythms of Body Temperature in the Free‐Ranging Raccoon Dog (Nyctereutes procyonoides) with Special Emphasis on Winter Sleep

The raccoon dog (Nyctereutes procyonoides) is the only canid with passive overwintering in areas with cold winters, but the depth and rhythmicity of wintertime hypothermia in the wild raccoon dog are unknown. To study the seasonal rhythms of body temperature (T_b), seven free‐ranging animals were captured and implanted with intra‐abdominal T_b loggers and radio‐tracked during years 2004–2006. The average size of the home ranges was 306±26 ha, and the average 24 h T_b was 38.0±<0.01°C during the snow‐free period (May–November). The highest and lowest T_b were usually recorded around midnight (21∶00–02∶00 h) and between 05∶00–11∶00 h, respectively, and the range of the 24 h oscillations was 1.2±0.01°C. The animals lost approximately 43±6% of body mass in winter (December–April), when the average size of the home ranges was 372±108 ha. During the 2–9‐wk periods of passivity in January–March, the average 24 h T_b decreased by 1.4–2.1°C compared to the snow‐free period. The raccoon dogs were hypothermic for 5 h in the morning (06∶00–11∶00 h), whereas the highest T_b values were recorded between 16∶00–23∶00 h. The range of the 24 h oscillations increased by approximately 0.6°C, and the rhythmicity was more pronounced than in the snow‐free period. The ambient temperature and depth of snow cover were important determinants of the seasonal T_b rhythms. The overwintering strategy of the raccoon dog resembled the patterns of winter sleep in bears and badgers, but the wintertime passivity of the species was more intermittent and the decrease in the T_b less pronounced.     

Effect of change in ambient temperature on core temperature during the daytime

In this study, the hypothesis is tested that continuous increases in ambient temperature (T_a) during daytime would give elevated core and skin temperatures, and consequently better thermal sensation and comfort. Rectal temperature (T_re), skin temperatures and regional dry heat losses at 7 sites were continuously measured for 10 Japanese male subjects in three thermal conditions: cond. 1, stepwise increases in T_a from 26 °C at 9 h00 to 30 °C at 18 h00; cond. 2, steady T_a at 28 °C from 9 h00 to 18 h00 and cond. 3, stepwise decreases in T_a from 30 °C at 9 h00 to 26 °C at 18 h00. Oxygen consumption was measured and thermal sensation and comfort votes were monitored at 15 min intervals. Body weight loss was measured at 1 h intervals. While T_re increased continuously in the morning period in any condition, it increased to a significantly greater (p?<?0.05) 36.9?±?0.3 °C at 18 h00 in cond. 1 relative to 36.7?±?0.28 °C in Cond. 2 and 36.5?±?0.37 °C in cond. 3. Better thermal comfort was observed in the afternoon and the evening in Cond.1 as compared with the other 2 conditions. Thus, a progressive and appropriate increase in T_a may induce optimal cycle in core temperature during daytime, particularly for a resting person.     

Regional differences in sweat rate response of steers to short-term heat stress

Six Angus steers (319 ± 8.5 kg) were assigned to one of two groups (hot or cold exposure) of three steers each, and placed into two environmental chambers initially maintained at 16.5–18.8°C air temperature (T _a). Cold chamber T _a was lowered to 8.4°C, while T _a within the hot chamber was increased to 32.7°C over a 24-h time period. Measurements included respiration rate, and air and body (rectal and skin) temperatures. Skin temperature was measured at shoulder and rump locations, with determination of sweat rate using a calibrated moisture sensor. Rectal temperature did not change in cold or hot chambers. However, respiration rate nearly doubled in the heat (P < 0.05), increasing when T _a was above 24°C. Skin temperatures at the two locations were highly correlated (P < 0.05) with each other and with T _a. In contrast, sweat rate showed differences at rump and shoulder sites. Sweat rate of the rump exhibited only a small increase with T _a. However, sweat rate at the shoulder increased more than four-fold with increasing T _a. Increased sweat rate in this region is supported by an earlier report of a higher density of sweat glands in the shoulder compared to rump regions. Sweat rate was correlated with several thermal measurements to determine the best predictor. Fourth-order polynomial expressions of short-term rectal and skin temperature responses to hot and cold exposures produced r values of 0.60, 0.84, and 0.98, respectively. These results suggest that thermal inputs other than just rectal or skin temperature drive the sweat response in cattle.     

Effect of sport practice and warm-up duration on the morning–evening difference in anaerobic exercise performance and perceptual responses to it

This study was designed to assess the effect of sport practice and warm-up duration on the morning–evening differences in muscle power and fatigue during performance of anaerobic exercise and perceptual responses to it. Twenty-two male physical education students – twelve trained (TG) (21.51 ± 1.25 years, 182.17 ± 4.37 cm and 82.88 ± 11.23 kg) and ten untrained (NTG) (23.89 ± 3.17 years, 176.8 ± 2.2 cm and 82.24 ± 8.43 kg) – participated in a crossover randomized study. They were asked to perform a 30-s Wingate test during six experimental sessions (three at 08:00 and three at 18:00 h) after different active warm-up (AWU) durations (5 min, 15 min, or 20 min). The AWU consisted of pedaling at a constant pace of 60 rpm against 50% of maximal aerobic power. Rate of perceived exertion (RPE) was recorded after the AWU and again immediately after the Wingate test. Heart rate and temperature (T) were recorded during each session at rest, after AWU and immediately at the end of the Wingate test. During the Wingate test, peak power (PP), mean power (MP), and the fatigue index were recorded. While the RPE estimations were higher in NTG, no time-of-day effect was recorded in either experimental group (morning or evening). T, PP, and MP were higher in the afternoon than in the morning (p < 0.001 for PP and MP; p < 0.05 for T). Similarly, PP and MP during the Wingate test were significantly higher in the TG than in the NTG (p < 0.001). The morning–evening difference of PP and MP was affected by AWU duration; AWU₁₅ was best in the morning for improving lower limb power for both the TG and NTG, whereas reducing this period to 5 min in the evening was appropriate for TG only.     

Rectal temperature, distal sweat rate, and forearm blood flow following mild exercise at two phases of the circadian cycle

Changes in rectal temperature during mild exercise in the middle of the rising (11:00 h) and falling (23:00 h) phases of the circadian rhythm of resting core temperature have been compared. Seven healthy males were studied at rest, while exercising on a cycle ergometer (60 min at 80 W), and during the first 30 min of recovery. Rectal temperature, forearm blood flow, and forearm sweat rate were measured at 1 min intervals throughout. During exercise, there were significant time-of-day differences in the profiles of all three variables, and in the thresholds for increases in forearm blood flow and sweating. Forearm blood flow and sweat rate were recruited more rapidly and to a greater extent with evening exercise, and rectal temperature rose less. Analysis of covariance, with rectal temperature as the covariate, indicated the associations between it and forearm blood flow or sweating were significantly different (p<0.05) between the two times of day. There were also significant (p<0.05) time-of-day effects for forearm blood flow and sweating that were independent of rectal temperature. During recovery, rectal temperature fell more quickly in the late evening than late morning. Forearm blood flow and sweating also showed time-of-day differences, but these did not co-vary with rectal temperature. Control of rectal temperature during exercise and recovery appears to be more effective in the late evening than late morning, and differences in forearm blood flow and sweating, as well as factors independent of these two variables, contribute to this difference. The results support our "heat-gain/heat-loss modes" hypothesis.     

Time-of-Day Effect on Cardiac Responses to Progressive Exercise

This study was designed to examine time-of-day effects on markers of cardiac functional capacity during a standard progressive cycle exercise test. Fourteen healthy, untrained young males (mean?±?SD: 17.9?±?0.7 yrs of age) performed identical maximal cycle tests in the morning (08:00–11:00?h) and late afternoon (16:00–19:00?h) in random order. Cardiac variables were measured at rest, submaximal exercise, and maximal exercise by standard echocardiographic techniques. No differences in morning and afternoon testing values at rest or during exercise were observed for oxygen uptake, heart rate, cardiac output, or markers of systolic and diastolic myocardial function. Values at peak exercise for Vo₂ at morning and afternoon testing were 3.20?±?0.49 and 3.24?±?0.55?L min^?1, respectively, for heart rate 190?±?11 and 188?±?15?bpm, and for cardiac output 19.5?±?2.8 and 19.8?±?3.5?L min^?1. Coefficients of variation for morning and afternoon values for these variables were similar to those previously published for test-retest reproducibility. This study failed to demonstrate evidence for significant time-of-day variation in Vo₂max or cardiac function during standard progressive exercise testing in adolescent males. (Author correspondence: thomas.rowland@bhs.org)     

Effect of time of day on soccer specific skills in children: psychological and physiological responses

The aim of this study was to examine the effect of time of day on soccer-specific skills and physiological and psychological parameters in children. Ten male children soccer players (age: 14.6?±?0.8 years; height: 1.63?±?0.4 m; body mass: 52.5?±?4.9 kg) performed two shooting accuracy tests before and after a 10?×?20-m dribbling sprint test with 20-s of passive recovery between repetitions. The measurements were taken at 08:00 h, 13:00 h, and 17:00 h in a randomized order. Mean heart rate (HR) was monitored during the dribbling test. At the beginning of each test session, blood pressure and intra-aural temperature were measured. Likewise, children were asked to complete the profile of mood state (POMS) and the Hooper Index questionnaires. Lactate concentration ([La]) was recorded at rest, post-fifth recovery periods and post-second accuracy test. Moreover, they indicate their rating of perceived exertion (RPE) score immediately at the end of each test session. The results of this study showed that dribbling performance was higher at 13:00 h and 17:00 h in comparison with 08:00 h (p?p?r?=?0.6, p?相似文献   

Effect of Time of Day on Aerobic Contribution to the 30‐s Wingate Test Performance

The purpose of this study was to evaluate the effects of time of day on aerobic contribution during high‐intensity exercise. A group of 11 male physical education students performed a Wingate test against a resistance of 0.087 kg · kg^?1 body mass. Two different times of day were chosen, corresponding to the minimum (06:00 h) and the maximum (18:00 h) levels of power. Oxygen uptake (V˙O₂) was recorded breath by breath during the test (30 sec). Blood lactate concentrations were measured at rest, just after the Wingate test, and again 5 min later. Oral temperature was measured before each test and on six separate occasions at 02:00, 06:00, 10:00, 14:00, 18:00, and 22:00 h. A significant circadian rhythm was found in body temperature with a circadian acrophase at 18:16±00:25 h as determined by cosinor analysis. Peak power (P_peak), mean power (P_mean), total work done, and V˙O₂ increased significantly from morning to afternoon during the Wingate Test. As a consequence, aerobic contribution recorded during the test increased from morning to afternoon. However, no difference in blood lactate concentrations was observed from morning to afternoon. Furthermore, power decrease was greater in the morning than afternoon. Altogether, these results indicate that the time‐of‐day effect on performances during the Wingate test is mainly due to better aerobic participation in energy production during the test in the afternoon than in the morning.     

Comparison of heat dissipation response between Malaysian and Japanese males during exercise in humid heat stress

This study investigated the differences in heat dissipation response to intense heat stress during exercise in hot and humid environments between tropical and temperate indigenes with matched physical characteristics. Ten Japanese (JP) and ten Malaysian (MY) males participated in this study. Subjects performed exercise for 60 min at 55% peak oxygen uptake in 32°C air with 70% relative humidity, followed by 30 min recovery. The increase in rectal temperature (T _re) was smaller in MY during exercise compared to JP. The local sweat rate and total body mass loss were similar in both groups. Both skin blood flow and mean skin temperature was lower in MY compared to JP. A significantly greater increase in hand skin temperature was observed in MY during exercise, which is attributable to heat loss due to the greater surface area to mass ratio and large number of arteriovenous anastomoses. Also, the smaller increase in T _re in MY may be explained by the presence of a significantly greater core–skin temperature gradient in MY than JP. The thermal gradient is also a major factor in increasing the convective heat transfer from core to skin as well as skin blood flow. It is concluded that the greater core–skin temperature gradient observed in MY is responsible for the smaller increase in T _re.     

Human thermoregulatory responses during prolonged walking in water at 25, 30 and 35°C

Eight healthy and physically well-trained male students exercised on a treadmill for 60 min while being immersed in water to the middle of the chest in a laboratory flowmill. The water velocity was adjusted so that the intensity of exercise correspond to 50% maximal oxygen uptake of each subject, and experiments were performed once at each of three water temperatures: 25, 30, 35°C, following a 30-min control period in air at 25°C, and on a treadmill in air at an ambient temperature of 25°C. Thermal states during rest and exercise were determined by measuring rectal and skin temperatures at various points, and mean skin temperatures were calculated. The intensity of exercise was monitored by measuring oxygen consumption, and heart rate was monitored as an indicator for cardiovascular function. At each water temperature, identical oxygen consumption levels were attained during exercise, indicating that no extra heat was produced by shivering at the lowest water temperature. The slight rise in rectal temperature during exercise was not influenced by the water temperature. The temperatures of skin exposed to air rose slightly during exercise at 25°C and 30°C water temperature and markedly at 35°C. The loss of body mass increased with water temperature indicating that both skin blood flow and sweating during exercise increased with the rise in water temperature. The rise in body temperature provided the thermoregulatory drive for the loss of the heat generated during exercise. Heart rate increased most during exercise in water at 35°C, most likely due to enhanced requirements for skin blood flow. Although such requirements were certainly smallest at 25°C water temperature, heart rate at this temperature was slightly higher than at 30°C suggesting reflex activation of sympathetic control by cold signals from the skin. There was a significantly greater increase in mean skin and rectal temperatures in subjects exercising on the treadmill in air, compared to those exercising in water at 25°C. Accepted: 22 May 1998     

Comparison of thermoregulatory responses to heat between Malaysian and Japanese males during leg immersion

The objective of this study was to investigate thermoregulatory responses to heat in tropical (Malaysian) and temperate (Japanese) natives, during 60 min of passive heating. Ten Japanese (mean ages: 20.8 ± 0.9 years) and ten Malaysian males (mean ages: 22.3 ± 1.6 years) with matched morphological characteristics and physical fitness participated in this study. Passive heating was induced through leg immersion in hot water (42°C) for 60 min under conditions of 28°C air temperature and 50% RH. Local sweat rate on the forehead and thigh were significantly lower in Malaysians during leg immersion, but no significant differences in total sweat rate were observed between Malaysians (86.3 ± 11.8 g m⁻² h⁻¹) and Japanese (83.2 ± 6.4  g m⁻² h⁻¹) after leg immersion. In addition, Malaysians displayed a smaller rise in rectal temperature (0.3 ± 0.1°C) than Japanese (0.7 ± 0.1°C) during leg immersion, with a greater increase in hand skin temperature. Skin blood flow was significantly lower on the forehead and forearm in Malaysians during leg immersion. No significant different in mean skin temperature during leg immersion was observed between the two groups. These findings indicated that regional differences in body sweating distribution might exist between Malaysians and Japanese during heat exposure, with more uniform distribution of local sweat rate over the whole body among tropical Malaysians. Altogether, Malaysians appear to display enhanced efficiency of thermal sweating and thermoregulatory responses in dissipating heat loss during heat loading. Thermoregulatory differences between tropical and temperate natives in this study can be interpreted as a result of heat adaptations to physiological function.     

Circadian variations in self-monitoring,a component of executive functions

The objective of this study was to identify circadian rhythms in self-monitoring, a component of executive functions. Participants were 10 undergraduate students, age: 18.5 ± 2.68 years, two male and eight female. They were recorded on a 30-h constant routine protocol; rectal temperature was recorded every minute and performance on a tracking task was assessed every 100 min. Self-monitoring indicators were adjustments of responses to random changes of speed and trajectory of a circle moving on the computer screen. Participants showed better accuracy during the afternoon, with decreases in the morning (06:20 and 08:00 h). These variations showed a phase delay of 2:29 ± 2:19 h with respect to the circadian rhythm of body temperature. In conclusion, there are circadian variations in self-monitoring. The decline in this component of executive functions could cause serious accidents among people working or studying during a morning shift, as well as commuting to and from work or school.     

The effect of heat stress on intestinal integrity and Salmonella invasion in broiler birds

The intestinal mucosa works as a barrier to protect the internal environment of the animal from bacteria and bacterial toxins found in the gut lumen. Heat stress may harm this function. Therefore, we designed the current experiment to investigate the effect of heat stress on intestinal integrity, physiological and immunological responses and Salmonella invasion in broiler chickens. At 26 days of age, 72 birds were randomly distributed into 3 treatments, with 8 replicates per treatment and 3 birds per replicate. The three treatments were control treatment; kept at thermoneutral environmental conditions (20 ± 2 °C), chronic heat stress treatment (exposed to 30 ± 2 °C; 24 h/day) and acute heat stress treatment (exposed to 35 ±2 °C from 09:00 to 13:00 and kept at 20 ± 1 °C from 13:00 to 09:00). The heat stress exposure was conducted for 10 successive days. Compared with the control treatment, birds subject to chronic and acute heat stress had reduced (P < 0.05) body weight and body gain and increased (P < 0.05) feed conversion ratio. However, feed intake and mortality rate were only increased (P < 0.05) in the acute heat stress treatment. Rectal temperature and Δ rectal temperature (°C/h) increased (P < 0.05) sharply during the first 2 days of exposure followed by gradual decreases until a plateau was achieved. Heat-stressed birds had increased (P < 0.05) serum concentrations of corticosterone, endotoxin lipopolysaccharide and the systemic inflammatory cytokine: TNF-α and IL-2, as well as a higher (P < 0.05) prevalence of Salmonella spp. in meat and livers, as compared with control treatment. It can be concluded that heat stress impaired intestinal integrity which resulted in increased intestinal permeability to endotoxin, translocation of intestinal pathogens (Salmonella spp.) and serum inflammatory cytokines. Therefore, avoiding thermal dysfunction of intestinal barrier is a significant factor in maintaining welfare, immune status and meat safety of broiler birds.