Investigation of factors affecting the rate of changes in endurance exercise performance by pre-cooling with ice slurry / 体力科学

To investigate the factors affecting the rate of improvement in endurance exercise performance following pre-cooling with ice slurry, we focused on individual physical characteristics and thermoregulatory capacity. Twenty-four healthy adults (12 males and 12 females) ingested 7.5g kg-1 of either ice slurry at -1°C (ICE) or control water at 20°C (CON) before cycling at 55% VO2max and continued cycling until the rectal temperature reached 38.5°C or untill exhaustion in a hot environment (controlled at 38°C, 40% relative humidity). The relationship between the rate of improvement in exercise performance and physical characteristics and thermoregulatory factors (changes in rectal temperature, the rate of rectal temperature increase, whole body sweat loss, mean metabolic heat production, and heat storage) was investigated. No correlation was noted between the rate of improvement in exercise performance and physical characteristics and heat storage. On the other hand, the rate of improvement in exercise performance showed significant correlations with changes in rectal temperature (r = -0.497), the rate of rectal temperature increases during exercise (r = -0.784), whole body sweat loss (r = 0.407), and mean metabolic heat production (r = -0.436). The rate of inhibition of sweating and the rate of increase in metabolic heat production by ice slurry ingestion during exercise have been suggested to be related to the rate of improvement in exercise performance. On the other hand, there was no relationship between body composition or VO2max and the rate of improvement in exercise performance.

Comparison of sweating components during endurance exercise under the same load in a hot environment and in a neutral thermal environment / 体力科学

Sweat contains electrolytes (minerals), therefore, it is necessary to consider its loss through sweat in the fluid replacement strategy in sports. The purpose of this study was to compare the concentration of components in sweat, such as electrolytes (minerals), when endurance exercise is performed in hot and neutral thermal environments. Eight men cycled for 60 min at 55% VO2peak under two envitonment conditions: a hot environment (WetBulb Globe Temperature (WBGT): 29.0±0.2℃; Heat) and a neutral thermal environment (WBGT: 20.5±0.2℃; Con). During exercise, sweat loss, core temperature, and heart rate (HR) were measured, and sweat from the chest, back, and thigh was collected. The core temperature, sweat loss, and HR increased significantly in Heat. The sweat electrolyte concentration was significantly higher in Heat than in Con only for Na. Regarding the amount of electrolyte loss from sweat, Na and K showed a significantly higher value than Con in Heat in comparison of each region, and the total loss amount of three regions in Cu also had a significantly higher value than Con in Heat. In addition, there was no difference in the concentration of Ca and Cu between the regions, but there was a significant difference in the amount of loss. It was concluded that even if there was no difference in the electrolyte concentration in sweat, the amount of electrolyte loss increased in K and Cu in a hot environment, and that there was a site difference in the amount of loss in Ca and Cu.

Effect of temperature for cooling leg on intermittent exercise performance during half-time in a hot environment / 体力科学

Intermittent exercise performance in a hot environment is lower than in temperate conditions. Cooling strategies at rest are important; however, the appropriate cooling temperature is not clear. The purpose of this study was to investigate the effect of temperature for cooling leg during half-time (HT) on intermittent exercise performance. Eleven men performed two pre-tests and three experimental trials of a 2 × 30 min intermittent exercise protocol in the heat (33°C; 50% relative humidity). During HT, three experimental conditions were set: no cooling (CON), cooling at the thigh using 12°C ice packs (COOL), and cooling at the thigh using 0°C ice packs (ICE) for 15 min. During the 2nd half, which consisted of 5 s maximal power pedaling every minute separated by 50 s of unloaded pedaling (80 rpm) and rest (5 s), the subjects repeated 2 × 15 sets of the intermittent exercise protocol. The peak power output under the COOL condition (694 ± 80 W) was significantly higher than that of the CON (653 ± 84 W). Thigh skin and deep temperatures showed a significant difference between each condition. In the COOL, thermal sensation was significantly lower, and thermal comfort was significantly higher. In a protocol that simulates intermittent athletic competitions such as soccer in a hot environment, using ice packs at 12°C to cool the thigh during HT lowered thigh skin and deep temperatures and improved heat perception and intermittent exercise performance. This cooling strategy is practical, suggesting that it would be effective for actual competitive situations.

Protective effect of qihuo decoction on the liver of rats with sleep deprivation in the humid and hot environment / 解放军医学杂志

Objective To explore the protective effect of Qihuo decoction (QHD) on the livers of sleep-deprived rats housed in the humid and hot environment, and to characterize ultrastructural changes of livers in these rats. Methods Forty male SD rats were randomized into 4 groups (10 each group): blank control group (BC group), humid and hot control group (HC group), humid and hot with sleep deprivation group (HS group), and humid and hot with sleep-deprived treated with QHD group (HSQ group). Rats in BC group were housed in the normal temperature and humidity chamber; while rats in HC group, HS group, and HSQ group were housed in the simulated hot and humid chamber. Rats in BC group, HC group, and HS group were given distilled water to gavage for 15 days, and rats in HSQ group were given QHD to gavage for 15 days. Then rats in HS group and HSQ group were sleep deprived for 72 hours. The serum concentrations of alanine aminotransferase (ALT) and serum aspartate aminotransferase (AST) were detected. The liver tissues contents of hepatic glycogen, malondialdehyde (MDA) and reduced glutathione (GSH) were detected. The expression of β-galactosidase (β-gal) in each group was also detected. Lastly, the rat hepatocytes ultrastructure was observed by a transmission electron microscope. Results In BC group, HC group, HS group, and HSQ group, the serum AST levels were (107.7±8.4)U/L, (126.9±10.4)U/L, (176.9±13.1)U/L, and (140.6±9.6)U/L; the ALT levels were (37.9±3.1)U/L, (45.5±6.2)U/L, (86.5±10.4)U/L, and (64.9±8.7)U/L. Statistical analysis among groups were significantly different (P<0.01). Compared with BC group, the levels of AST and ALT increased significantly in the rest 3 groups (P<0.01). The serum concentrations of AST and ALT in HSQ group were significantly lower than those in HS group (P<0.01). The hepatic glycogen levels were (19.7±1.5)nmol/mg prot, (17.9±0.8) nmol/mg prot, (11.3±0.5)nmol/mg prot, (14.6±0.7)nmol/ mg prot successively in the four groups. The MDA levels were (10.3±1.1)nmol/mg prot, (26.6±1.3)nmol/mg prot, (41.4±2.4) nmol/mg prot, (33.7±1.7)nmol/mg prot successively in the four groups. The GSH levels were (77.6±5.2)U/mg prot, (70.6±5.1) U/mg prot, (45.8±3.8)U/mg prot, (60.7±3.3)U/mg prot successively in the four groups. Comparisons among groups were significantly different (P<0.01). Compared with BC group, the data of HC group, HS group and HSQ group about the contents of hepatic glycogen and GSH decreased significantly (P<0.05), the contents of MDA increased significantly (P<0.01). Compared with HS group, the data of HSQ group about the contents of hepatic glycogen and GSH increased significantly (P<0.01), the contents of MDA decreased significantly (P<0.01). The counts of β-gal positive cells were (0.67±0.52), (6.23±0.42), (13.5±0.48) and (10.16±0.36) successively in rats liver tissues of the four groups. Comparison among groups was significantly different (P<0.01). Compared with the BC group, the data of the HC group, HS group, and HSQ group about the number of β-gal positive cells increased significantly (P<0.01). The number of β-gal positive cells in HSQ group was lower than that in HS group (P<0.01). Light microscopy and transmission electron microscopy showed that the hepatocytes of HC group, HS group and HSQ group were damaged to varying degrees, and the injury of HS group was the most obvious, and the injury of HSQ group was reduced. Conclusion QHD Can obviously alleviate the degree of liver injury that was induced by high temperature and high humidity and sleep deprivation, and the mechanism of which might be related to increasing hepatic glycogen reserve, balancing oxidative stress and slowing process of hepatic cell aging.

Protective effect of curcumin on the intestinal injury and oxidative stress in rats in dry and hot desert environment / 中国比较医学杂志

Objective To investigate the protective effect of curcumin pretreatment on the intestinal mucosa in rats in dry and hot desert environment. Methods Eighty male SPF grade rats were randomly divided into saline control group ( NC group) and curcumin pretreatment group ( HDC group ) ( 40 in each group ) . Rats in the NC group were gavaged with saline, and rats in the HDC group were gavaged with curcumin (200 mg/kg), once a day for 7days. The rats were placed in a cabin simulating the dry and hot desert environment (41 ± 0. 5)℃ and relative humidity of (10 ± 2)%. Rats were randomly taken from each groups ( n=10 ) and sacrificed with 3% sodium pentobarbital intraperitoneally at 0 min, 50 min, 100 min and 150 min time points. The ileal tissue was stained for histological examination and oxidative stress index was detected. Results At time points 0 min and 50 min, the pathological injury scores of the HDC group were not significantly different compared with the NC group (P > 0. 05). At time points 100 min and 150 min, the pathological injury scores of the HDC group were significantly decreased compared with the NC group ( P < 0. 01 ) . At time points 50 min, 100 min and 150 min, the CAT and SOD activity of HDC group were significantly increased compared with the NC group (P< 0. 05 or P< 0. 01). The MDA content of HDC group were significantly decreased compared with the NC group ( P< 0. 05 or P < 0. 01 ) . Exposed to dry and hot environment, the pathological injury scores of the NC group were negatively correlated with CAT and SOD activity (r= -0. 9128, r= -0. 9125, P< 0. 01), and positively correlated with MDA content (r=0. 9258, P< 0. 01). Conclusions Curcumin pretreatment can protect the intestinal mucosa of rats in dry-heat environment of desert, and curcumin can alleviate the pathological damages of intestinal mucosa by inhibiting the oxidative stress in intestinal mucosa.

The Effect of Various Hot Environments on Physiological Responses and Information Processing Performance Following Firefighting Activities in a Smoke-Diving Room

BACKGROUND: Fire service workers often implement multiple duties in the emergency conditions, with such duties being mostly conducted in various ambient temperatures. METHODS: The aim of the current study was to assess the firefighters' physiological responses, information processing, and working memory prior to and following simulated firefighting activities in three different hot environments. Seventeen healthy male firefighters performed simulated firefighting tasks in three separate conditions, namely (1) low heat (LH; 29–31°C, 55–60% relative humidity), (2) moderate heat (MH; 32–34°C, 55–60% relative humidity), and (3) severe heat (SH; 35–37°C, 55–60% relative humidity). It took about 45–50 minutes for each firefighter to finish all defined firefighting activities and the paced auditory serial addition test (PASAT). RESULTS: At the end of all the three experimental conditions, heart rate (HR) and tympanic temperature (TT) increased, while PASAT scores as a measure of information processing performance decreased relative to baseline. HR and TT were significantly higher at the end of the experiment in the SH (159.41 ± 4.25 beats/min; 38.22 ± 0.10°C) compared with the MH (156.59 ± 3.77 beats/min; 38.20 ± 0.10°C) and LH (154.24 ± 4.67 beats/min; 38.17 ± 0.10°C) conditions (p 0.05). Nonetheless, there was a measurable difference in PASAT scores between LH and SH (p < 0.05). CONCLUSION: These consequences demonstrate that ambient temperature is effective in raising the physiological responses following firefighting activities. It is therefore argued that further increase of ambient temperature can impact firefighters' information processing and working memory during firefighting activity.

Hypertension is associated with greater heat exchange during exercise recovery in a hot environment

Individuals with systemic arterial hypertension have a higher risk of heat-related complications. Thus, the aim of this study was to examine the thermoregulatory responses of hypertensive subjects during recovery from moderate-intensity exercise performed in the heat. A total of eight essential hypertensive (H) and eight normotensive (N) male subjects (age=46.5±1.3 and 45.6±1.4 years, body mass index=25.8±0.8 and 25.6±0.6 kg/m2, mean arterial pressure=98.0±2.8 and 86.0±2.3 mmHg, respectively) rested for 30 min, performed 1 h of treadmill exercise at 50% of maximal oxygen consumption, and rested for 1 h after exercise in an environmental chamber at 38°C and 60% relative humidity. Skin and core temperatures were measured to calculate heat exchange parameters. Mean arterial pressure was higher in the hypertensive than in the normotensive subjects throughout the experiment (P<0.05, unpaired t-test). The hypertensive subjects stored less heat (H=-24.23±3.99 W·m−2vs N=-13.63±2.24 W·m−2, P=0.03, unpaired t-test), experienced greater variations in body temperature (H=-0.62±0.05°C vsN=-0.35±0.12°C, P=0.03, unpaired t-test), and had more evaporated sweat (H=-106.1±4.59 W·m−2vs N=-91.15±3.24 W·m−2, P=0.01, unpaired t-test) than the normotensive subjects during the period of recovery from exercise. In conclusion, essential hypertensive subjects showed greater sweat evaporation and increased heat dissipation and body cooling relative to normotensive subjects during recovery from moderate-intensity exercise performed in hot conditions.

Study on rectal temperature and scores of comprehensive sensation during heat acclimatization training in artificial hot-humid environment / 第二军医大学学报

Objective To study the relationship between adaptability improvement to hot-humid environment with the changes of rectal temperature, heart rate, and scores of comprehensive sensation before and after training in hot-humid environment. Methods Thirty healthy male university students were trained and tested under a temperature of 39.0°C and a relative humidity of 80.00% for a week. Their rectal temperature, heart rate, and scores of comprehensive sensation were monitored every time before and after training. The obtained data were subjected to ANOVA analysis and Tukey-tests. The improvement rate of rectal temperature and improvement rate of comprehensive sensation scores were calculated each time after training in hot-humid environment. Results and conclusion We found that rectal temperature and scores of comprehensive sensation were consistent in demonstrating the improvement of the adaptability to hot-humid. It is suggested that rectal temperature and scores of comprehensive sensation should be used as reference standards for adaptability improvement to hot-humid environment, and heart rate is not recommended, but the combination of three indices should be used as safety control standard.

THE GENDER DIFFERENCES IN THERMOREGULATORY RESPONSES DURING EXERCISE RECOVERY / 体力科学

The purpose of this study was to investigate the gender differences in thermoregulatory responses during the recovery from prolonged exercise. Fourteen (7 males and 7 females) subjects cycled for 45 minutes at 55%VO₂max and then rested for 105 minutes in the hot and humid environment (30℃, 80% relative humidity) or cool environment (20℃, 60% relative humidity). Both males and females showed same variations in rectal temperature (Tre) during exercise and recovery periods. Total sweat volume and water intake were significantly larger in males than in females during recovery in the both environments. In the heat condition, mean skin temperature (Tsk) decreased immediately after the cessation of exercise in females but not in males (the recovery period (R) 5–15 min : <i>p</i><0.01, R15–20 min : <i>p</i><0.05). These results suggested there are gender-related differences in the mechanisms and also the process maintaining the balance of heat production and heat loss response during recovery from prolonged exercise. Moreover the heat might modify gender differences of heat loss response during recovery as an important factor.

Effects of carbohydrate and electrolyte solution replacement on metabolic and hormonal responses after a moderate endurance run in hot outdoor conditions / 体力科学

The effect of ingestion of a chilled carbohydrate and electrolyte solution on metabolic and hormonal responses and water-electrolyte balance was studied after two 5-km runs in hot outdoor conditions (Temp, 30.6-30.9°C ; humidity, 61.3-62.4%) . Eight healthy females (mean age 21.8 years) participated in : 1) a control experiment (Copt) with no fluid intake, 2) an experiment with 500 ml of tap water (WI), and 3) an experiment with 500 ml of sports beverage (SB) containing carbohydrate and electrolytes each of which were given after the 1st 5-km run, followed by a second 5-km run with an equivalent to 68.7-72.3% of VO<SUB>2</SUB>max. In the Cont, decreases in %ΔPV and blood glucose (BS) and increases in serum osmolality (Sosm), free fatty acid (sFFA) and plasma hormone concentrations related to regulation of the water-electrolyte balance in the body persisted after the 2 nd run. The intake of the sports beverage prevented hypoglycemia and ketoacidosis, as shown by an increase in sFFA and positive results for qualitative analysis of ketone body in the urine, and quick recovery of plasma volume following an endurance run under a hot environment. This study suggests that fluid replacement with a sports beverage containing carbohydrate and electrolytes was superior to plain water or no fluid ingestion in terms of metabolic and hormonal responses and the recovery of plasma volume and elevated rectal temperature following an endurance run under hot conditions.

Relationship between drinking behavior and body temperature during exercise in heat / 体力科学

Effects of drinking on body temperature during exercise and recovery in heat were studied in the field. Five healthy baseball players participated in baseball training with and without fluid re-placement on summer days, and rectal temperature, body weight loss, rating of thirst and the amount of water consumption were measured.<BR>The rectal temperature was significantly lower throughout exercise when fluid replacements were allowed. The normalization of rectal temperature during rest periods was also significantly accelerated by fluid replacement. The rating of thirst was significantly correlated with the increase in rectal temperature and sweat loss, and also with the volume of fluid intake. Although full rehydration was not observed, body fluid replacement by drinking is suggested to be advantageous for body temperature regulation during exercise in heat.

Cardiovascular function during kendo exercise in a hot environment. Effects of water replacement / 体力科学

A study was carried out to examine the effects of water replacement on cardiovascular function during kendo practice in a hot environment. Five male college kendoists performed moderately severe 30-min kendo practice at a WBGT index of about 27°C with and without water intake. For water replacement, the subjects ingested 700 ml water (500 ml before exercise and 200 ml at 15 min after the start of exercise) . Under both conditions, body weight was decreased significantly, and hematocrit and serum total protein concentration were increased significantly after the exercise. With water replacement, the body weight loss induced by the exercise was similar to that under water deprivation. However, the decrease in body weight from the basal body weight, i. e. body weight measured before water intake, was significantly less with water replacement than under water deprivation. There were no significant differences in the percentage increases of hematocrit and serum total protein concentration between the two conditions, although the percentage change in plasma vasopressin concentration was significantly lower with water replacement than without. In the subjects deprived of water, the left ventricular end-diastolic dimension and left atrial dimension were significantly reduced after the exercise, and stroke volume, ejection fraction, and fractional shortening were also decreased significantly. The ratio of left ventricular end-systolic wall stress to left ventricular end-systolic volume index was increased significantly after the exercise without water intake. With water replacement, however, the percentage decreases in cardiac dimensions, stroke volume, ejection fraction, and fractional shortening were significantly lower than those under water deprivation. There was no significant change in the ratio of left ventricular end-systolic wall stress to left ventricular end-systolic volume index before and after the exercise with water intake. It is suggested that 700 ml water replacement before and during kendo exercise in a hot environment prevents depletion of stroke volume and deterioration of cardiovascular function, although it might not improve significantly the plasma volume loss after exercise.

The effect of different environmental conditions on blood lactate accumulation, LT and OBLA during incremental exercise / 体力科学

The purpose of this study was to compare blood lactate concentration, lactate threshold (LT) and onset of blood lactate accumulation (OBLA) during an incremental bicycle exercise under a hot dry environment with those during the same workload under a thermoneutral environment. Eight unacclimated men performed an incremental test to exhaustion on a cycle ergometer during which the work rate was increased by 30 W every three minutes under thermoneutral (25°C) and hot dry (40°C) environmental conditions. Oxygen consumption (VO<SUB>2</SUB>) -pulmonary ventilation (VE), gas exchange measures and earlobe blood samples for lactate analysis were obtained every minute during the test. LT (p<0.05) and OBLA (p<0.01) occurred at significantly lower VO<SUB>2</SUB> under the hot environment than those under the thermoneutral environment. Additionally blood lactate concentration was significantly higher (p<0.05) at each measurement period under the hot environment compared with that under the ther-moneutral environment. The correlation between LT and ventilatory threshold (VT) was not statistically significant under the thermoneutral (r=0.20) and hot dry (r=0.60) environments, These findings demonstrate that the hot dry environment may increase blood lactate concentration more and causes a leftward shift of LT and OBLA. Since blood lactate accumulation during incremental exercise is not considered to be the only factor which mediates VE, VT does not always accurately predict LT.

Effects of prolonged kendo practice in a hot environment on cardiovascular function / 体力科学

To study the effects of prolonged kendo practice in a hot environment on cardiovascular function, certain hemodynamic parameters were measured in 5 male college kendo fencers before and after 1 hour of kendo practice performed at a dry bulb temperature of 30.4t and wet bulb temperature of 26.2°C After kendo practice, body weight was significantly decreased and both hematocrit and blood viscosity were significantly increased. The left ventricular end-diastolic dimension and the left atrial dimension, measured by echocardiography, were significantly reduced after kendo practice, and stroke volume, ejection fraction, and fractional shortening were also significantly decreased after practice. The same fencers were subjected to lower body negative pressure testing designed to reduce the left ventricular end-diastolic dimension to the same degree as kendo practice, and comparable decreases in stroke volume, ejection fraction, and fractional shortening were observed. The ratio of end-systolic wall stress to end-systolic volume index was significantly increased during both kendo practice and lower body negative pressure testing. We conclude that prolonged kendo practice in a hot environment impairs cardiac pump function by reducing preload in parallel with the decrease in venous return, that myocardial contractility may not deteriorate despite marked hemoconcentration, and that fluid intake during practice may prevent deterioration of cardiovascular function.

STUDIES ON THE EFFECT OF POTASSIUM DEFICIENCY AND POTASSIUM REQUIREMENTS IN HOT ENVIRONMENTS / 营养学报

Potassium metabolism in young adult men exercising in the heat for six consecutive days and the effect of potassium deficiency in mice and rats induced by low potassium diet during heat exposure were observed. Increased potassium loss in sweat and lower potassium intake resulted in negative potassium balance. Individuals with a negative potassium balance had lower se- rum potassium levels and higher body temperature after exercise. Potassium deficient mice accomplished less work done (2.372 vs 4.253 Kg.M) but exih-ibited a markedly greater rate of heat gain (1.36 vs 0.87℃/Kg.M) as compared to the controls. The survival rate and cellular energy metabolism also decreasedThese observations suggest that prevention from potassium deficiency must be emphasized during prolonged physical activity under hot environments. According to the linear regression equations between potassium intake and balance, it is proposed that the potassium requirements in mild and medium physical activity in the heat are 40 and 60 mEq/day respectively, and the allowance of potassium in the latter may be 70-80 mEq/day.