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.     

Physiological reaction of women during exercise and recovery, in a comfortable environment and a hot environment

Physiological reaction and oxygen intake during exercise and recovery were measured in fourteen young female Japanese during the follicular phase of their menstrual cycle at 25 degree C with 50% relative humidity and at 35 degree C with 50% relative humidity. Subjects, clad in bathing suits only, performed a bicycle ergometer exercise at a constant work load of 600 kg . m/min at a cycling rate of 50 rpm for 20 min and recovered while remaining on the bicycle ergometer for 40 min. The mean values of sweat volume and skin temperature were significantly greater at 35 degree C than at 25 degree C. It has been shown that heart rate and rectal temperature during exercise were slightly higher at 35 degree C than at 25 degree C, while those during recovery were significantly higher at 35 degree C than at 25 degree C. Oxygen intake, oxygen debt, and the fall in diastolic blood pressure after exercise were considerably greater at 35 degree C than at 25 degree C. The increase in oxygen intake in a hot environment might result from an increased metabolism due to higher body temperature and increased energy requirement for heat dissipation such as profuse sweating, higher heart rate, and increased ventilatory volume. The increase in oxygen debt in a hot environment might reflect the increased metabolism caused by higher body temperature and the increased production of lactic acid in the working muscle as a result of an insufficient blood supply to the muscle. The increases in sweat volume, oxygen intake during exercise, and oxygen debt in women in a hot environment were considerably smaller than corresponding values for men. The smaller increase in sweat volume in women in a hot environment could reflect a smaller oxygen intake and a more marked dilation of skin vessels in women than in men.     

Skin blood flow during incremental exercise in a thermoneutral and a hot dry environment

Eight physically fit men performed two incremental bicycle ergometer tests, one in an ambient temperature of 25 degrees C and the other at 40 degrees C. Oesophageal temperature (Tes) increased continuously throughout the tests up to 38.0 and 38.3 degrees C, respectively. In both environments, forearm blood flow (plethysmography) was linearly related to Tes above the Tes threshold for vasodilation, but at the heaviest work loads this relationship was clearly attenuated and therefore indicated skin vasoconstriction, which tended to be more pronounced at 25 degrees C. During recovery at 25 degrees C, in some subjects the forearm blood flow increased above the levels observed at the end of the graded exercise in spite of a decreasing Tes. Skin blood flow, measured by laser Doppler flow meter at the shoulder, was quantitatively different but, on average, seemed to reveal the same response pattern as the forearm blood flow. In spite of the higher level of skin blood flow in the heat, blood lactate accumulation did not differ between the two environments. The present results suggest that there is competition between skin vasoconstriction and vasodilation at heavy work rates, the former having precedence in a thermoneutral environment to increase muscle perfusion. During short-term graded exercise in a hot environment, skin vasoconstriction with other circulatory adjustments seems to be able to maintain adequate muscle perfusion at heavy work levels, but probably not during maximum exercise.     

Characteristics of body heat balance of paraplegics during exercise in a hot environment

The purpose of this investigation was to clarify the characteristics of body temperature regulation in paraplegics due to spinal cord injury (SCI) during an arm cranking exercise in a hot environment. Twelve paraplegics with lesions located between Th3 and L1,2 and seven able-bodied subjects (AB) participated in this study. The subjects were exposed to a hot (33 degrees C) or a moderate temperature (25 degrees C) environment for one hour and during the last 10 min of the exposure, the subjects performed arm cranking exercises at an exercise intensity of 40 W. The skin temperatures at the chest, the upper arm, the thigh and the calf, the tympanic membrane temperature (Tty), and the skin blood flow of the thigh (SBFT) were continuously monitored during the experiment. Although no systematical variation was found in the Tty at 25 degrees C, the Tty at 33 degrees C in paraplegics during exercise was significantly greater than that at rest (P < 0.01), which indicated a pronounced heat stress for paraplegics at 33 degrees C. SBFT of paraplegics with high lesions of the SCI remained unchanged during the experiment at 25 degrees C and 33 degrees C, while paraplegics with low lesions in this study showed consecutive increases in SBFT during exercise in both environmental conditions similar to AB. The increased core temperature in paraplegics with high lesions was considered to be due to a lack of sweat response and vasomotor activity in the paralyzed area. On the basis of the findings in this study, it can be suggested that high core temperature without any increment of SBFT may be characterized as body heat balance of paraplegics with high lesions during exercise in a hot environment.     

Effect of continuous negative-pressure breathing on skin blood flow during exercise in a hot environment

To assessthe impact of continuous negative-pressure breathing (CNPB) on theregulation of skin blood flow, we measured forearm blood flow (FBF) byvenous-occlusion plethysmography and laser-Doppler flow (LDF) at theanterior chest during exercise in a hot environment (ambienttemperature = 30°C, relative humidity = ~30%). Seven malesubjects exercised in the upright position at an intensity of 60% peakoxygen consumption rate for 40 min with and without CNPB after 20 minof exercise. The esophageal temperature(T_es) in both conditionsincreased to 38.1°C by the end of exercise, without any significantdifferences between the two trials. Mean arterial pressure (MAP)increased by ~15 mmHg by 8 min of exercise, without any significantdifference between the two trials before CNPB. However, CNPB reducedMAP by ~10 mmHg after 24 min of exercise (P < 0.05). The increasein FBF and LDF in the control condition leveled off after 18 min ofexercise above a T_es of37.7°C, whereas in the CNPB trial the increase continued, with arise in T_es despite the decreasein MAP. These results suggest that CNPB enhances vasodilation of skinabove a T_es of ~38°C bystretching intrathoracic baroreceptors such as cardiopulmonarybaroreceptors.

     

Thermoregulatory responses during exercise and a hot water immersion and the affective responses to peripheral thermal stimuli

Tympanic (Tty), mean skin (¯Tsk) and mean body (¯Tb) temperatures and heart rate (HR) increased more in low Vo₂ max group (LG) than in high Vo₂ max group (HG) during exercise. The regression coefficient of body temperatures (Tty and ¯Tb) on HR and the increased rate of heat storage were larger in LG than in HG during exercise. The local sweat rate (per min/cm²) during a hot water bath exhibited a considerable large quantity in comparison with the amount during exercise. Internal and skin temperatures during a hot water bath increased more immediately than those during exercise. The levels of comfort sensation during the preovulatory phase in women and pre-exercise period in men were higher at 40C than at 20C as peripheral thermal stimulus. The levels during the postovulatory and post-exercise phases in the same subjects were higher with the cool stimuli than with the warm stimuli. Above results suggest that thermoregulatory responses during submaximal exercise are different according to physical fitness and that these responses are different from those during hot water immersion. In addition, these suggest that the scores of thermal sensation with warm and cool stimuli are different during the pre- and post-ovulatory phases and the pre- and post-exercise periods.     

Effects of profuse sweating induced by exercise on urinary uric acid excretion in a hot environment

In order to determine whether exercise-induced profuse sweating could reduce urinary uric acid excretion, we simulated badminton players training and measured their uric acid in urine, sweat and blood during the training period. Thirteen male volunteers who were well-trained badminton players were recruited in this study. On the first 2 days and the last 2 days of the study period none of the subjects engaged in any intense exercise- or activity-inducing profuse sweat, but they accepted routine training 2 h per day during the middle 3 days. The results show that mean serum urate levels of thirteen volunteers rose significantly on day 4, when the concentrations increased by 18.2% over day 2 (P < 0.05). The mean ten-hour urinary uric acid excretion of seven volunteers on the 3 training days was significantly less at 178.5 micromol/day and 118.3 micromol/day than those on the preceding and subsequent days of the training days, respectively (P < 0.05). Furthermore, for six volunteers, the mean ratio of clearance of uric acid to creatinine was 6.6% on day 2, which significantly decreased to 5.4% on day 4 (P < 0.05). It is concluded profuse sweating exercise results in a decrease of urinary uric acid excretion amounts and leads to increased serum uric acid after the exercise. We suggest that persons who take vigorous exercise or are exposed to hot environments need drinking enough fluids to prevent dehydration and maintain adequate urinary output. People with profuse sweat after rigorous exercise are recommended taking sports drinks containing abundant sodium in order to decrease serum uric acid.     

Effects of menstrual cycle and physical training on heat loss responses during dynamic exercise at moderate intensity in a temperate environment

We evaluated the effects of the menstrual cycle and physical training on heat loss (sweating and cutaneous vasodilation) responses during moderate exercise in a temperate environment. Ten untrained (group U) and seven endurance-trained (group T) women (maximal O2 uptake of 36.7+/-1.1 vs. 49.4+/-1.7 ml.kg-1.min-1, respectively; P<0.05) performed a cycling exercise at 50% maximal O2 uptake for 30 min during both the midfollicular and midluteal menstrual phase in a temperate environment (ambient temperature of 25 degrees C, relative humidity of 45%). In group U, plasma levels of estrone, estradiol, and progesterone at rest and esophageal temperature (Tes) during exercise were significantly higher during the midluteal than during the midfollicular phase (P<0.05). Sweating rate and cutaneous blood flow (measured via laser-Doppler flowmetry) on the chest, back, forearm, and thigh were lower during the midluteal than during the midfollicular phase during exercise. Tes threshold for heat loss responses was significantly higher and sensitivity of the heat loss responses was significantly lower in the midluteal than in the midfollicular phase, regardless of body site. These effects of the menstrual cycle in group U were not observed in group T. The sweating rate and cutaneous blood flow were significantly higher in group T than in group U, regardless of menstrual phase or body site. Tes threshold for heat loss responses was significantly lower and sensitivity of heat loss responses was significantly greater in group T than in group U in the midluteal phase; however, sensitivity of the sweating response was significantly greater in the midfollicular phase. These results suggest that heat loss responses in group U were inhibited in the midluteal phase compared with in the midfollicular phase. Menstrual cycle had no remarkable effects in group T. Physical training improved heat loss responses, which was more marked in the midluteal than in the midfollicular phase.     

Seasonal effects of sleep deprivation on thermoregulatory responses in a hot environment

Effects of sleep deprivation and season on thermoregulation during 60 min. of leg-bathing (water temperature of 42 degrees C, air temperature of 30 degrees C, and relative humidity of 70%) were studied in eight men who completed all 4 experiments for normal sleep and sleep deprivation in summer and winter. Rectal temperature (T(re)), skin temperature, total body sweating rate (M(sw-t)), local sweating rate on the back (M(sw-back)) and forearm (M(sw-forearm)), and skin blood flow on the back (SBF(back)) and forearm (SBF(forearm)) were measured. The changes in T(re) (DeltaT(re)) were smaller (P<0.05) for sleep deprivation than for normal sleep regardless of the season. This decrease in DeltaT(re) was significant only in summer (P<0.05). Mean skin temperature (T(mean of)(sk)) was higher (P<0.05) for sleep deprivation than for normal sleep regardless of the season. M(sw-t) was smaller (P<0.05) for sleep deprivation than for normal sleep regardless of season, although M(sw-back) and M(sw-forearm) were similar. SBF(back) and SBF(forearm) tended to be higher for sleep deprivation than normal sleep. The sensitivity of SBF to T(re) was higher (P<0.05) for sleep deprivation than for normal sleep. These data indicate that seasonal differences in thermoregulation were small because of morning time. Sleep deprivation increased dry heat loss and restrained T(re) rise, in spite of decreased sweating rate.     

The effects of wind and thermal radiation on thermal responses during rest and exercise in a cold environment

1. 1. The purpose of this study was to investigate the effects of thermal radiation and wind on thermal responses at rest and during exercise in a cold environment.

2. 2. The experimental conditions were radiation and wind (R + W), no radiation and wind (W), radiation and no wind (R), no radiation and no wind (C).

3. 3. The air temperature was −5°C. Thermal radiation was 360 W/m². Air velocities were 0.76, 1.73 and 2.8 m/s. Rectal and skin temperatures, heart rate and oxygen consumption were recorded. Thermal and comfort sensations were questioned.

4. 4. There are no significant effects of thermal radiation and wind on the physiological responses except the mean skin temperature. There are significant effects on the mean skin temperature (P < 0.01) and thermal sensation (P < 0.05).

Effects of estrus cycle on thermoregulatory responses during exercise in rats

In female rats, rectal temperature (Tre), tail vasomotor response, oxygen uptake (VO2), and carbon dioxide production (VCO2) were measured in proestrus and estrus stages during treadmill running at two different speeds at an ambient temperature (Ta) of 24 degrees C. Experiments were performed at 2.00-6.00 a.m., when the difference in Tre was greatest between the two stages; Tre at rest in the estrus stage was 0.54 degrees C higher than in the proestrus stage. In a mild warm environment, threshold Tre for a rise in tail skin temperature (Ttail) was also higher in the estrus stage than in the proestrus stage. In contrast, no difference was seen in the threshold Tre and steady state Tre at the end of exercise between proestrus and estrus stages. These values were higher at the higher work intensity. VO2 was also similar between the two stages, except in the second 5 min after the beginning of exercise, when VO2 was greater and Tre rose more steeply in the proestrus stage. These data indicate that deep body temperature during exercise is regulated at a certain level depending on the work intensity and is not influenced by the estrus cycle.     

Comparison of techniques for the measurement of skin temperature during exercise in a hot,humid environment

Exercising or working in a hot, humid environment can results in the onset of heat-related illness when an individual''s temperature is not carefully monitored. The purpose of the present study was to compare three techniques (data loggers, thermal imaging, and wired electrodes) for the measurement of peripheral (bicep) and central (abdominal) skin temperature. Young men and women (N = 30) were recruited to complete the present study. The three skin temperature measurements were made at 0 and every 10-min during 40-min (60% VO₂max) of cycling in a hot (39±2°C), humid (45±5% RH) environment. Data was statistically analyzed using the Bland-Altman method and correlation analysis. For abdominal skin temperature, the Bland-Altman limits of agreement indicated that data loggers (1.5) were a better index of wired than was thermal imaging (3.5), For the bicep skin temperature the limits of agreement was similar between data loggers (1.9) and thermal (1.9), suggesting the both were suitable measurements. We also found that when skin temperature exceeded 35°C, we observed progressively better prediction between data loggers, thermal imaging, and wired skin sensors. This report describes the potential for the use of data loggers and thermal imaging to be used as alternative measures of skin temperature in exercising, human subjects.