Thermal and metabolic responses to cold by men and by eumenorrheic and amenorrheic women

Thermal stress associated mortality risk and effect modification by sex and obesity in an elderly cohort of Chinese in Hong Kong

We assessed the effects of apparent temperature (AT) on mortality and the effect modifications attributable to individual characteristics in Hong Kong with subtropical climate conditions. Two datasets are used for analyses: one from mortality data of the general elderly population in 1998-2009; the other from an elderly cohort with 66,820 subjects recruited in 1998-2001 with mortality outcomes followed up until 2009. We found that AT below 20.8 °C was associated with an increase in mortality risk of 1.99% (95% confidence interval: 0.64%, 2.64%) for all causes, 2.48% (0.57%, 4.36%) for cardiovascular disease, and 3.19% (0.59%, 5.73%) for respiratory disease for every 1 °C decrease in AT over the following 3 days. The associations were modified by sex and body mass index, in particular stronger associations were observed for females and for obese subjects.

Environmental effects on brain function

Environmental extremes can result in local and systemic illness, or even death. A majority of cases involving environmental mishap are related to excessive heat, cold, or high altitude exposure. Heat- or cold-related illness occurs when the body's homeostatic mechanisms are overwhelmed, resulting in an accumulation or loss of heat, respectively. Altitude illness results from a combination of low temperature and hypoxia. All three environmental injuries have significant effects upon brain function. This article discusses the pathophysiology of heat, cold, and altitude illness and their effects upon brain function.

American College of Sports Medicine position stand: prevention of cold injuries during exercise

It is the position of the American College of Sports Medicine that exercise can be performed safely in most cold-weather environments without incurring cold-weather injuries. The key to prevention is use of a comprehensive risk management strategy that: a) identifies/assesses the cold hazard; b) identifies/assesses contributing factors for cold-weather injuries; c) develops controls to mitigate cold stress/strain; d) implements controls into formal plans; and e) utilizes administrative oversight to ensure controls are enforced or modified. The American College of Sports Medicine recommends that: 1) coaches/athletes/medical personnel know the signs/symptoms and risk factors for hypothermia, frostbite, and non-freezing cold injuries, identify individuals susceptible to cold injuries, and have the latest up-to-date information about current and future weather conditions before conducting training sessions or competitions; 2) cold-weather clothing be chosen based on each individual's requirements and that standardized clothing ensembles not be mandated for entire groups; 3) the wind-chill temperature index be used to estimate the relative risk of frostbite and that heightened surveillance of exercisers be used at wind-chill temperatures below -27 degrees C (-18 degrees F); and 4) individuals with asthma and cardiovascular disease can exercise in cold environments, but should be monitored closely.

Temperature regulation during rest and exercise in the cold in premenarcheal and menarcheal girls

Temperature regulation during exercise in the cold was examined in 13 adolescent female individuals, aged 13-18 yr. Six girls with established menstrual cycles comprised the eumenorrheic menarcheal (EM) group, and seven nonmenstruating girls comprised the premenarcheal (PM) group. During the first visit, maximal oxygen consumption (V̇o2 max), height, weight, and percent body fat were measured. The second visit included a determination of metabolic rate in thermoneutrality (21°C), consisting of a 10-min rest period and 20 min of cycling (30% of V̇o2 max), and a cold test (5°C, 40% humidity, <0.3 m/s air velocity) involving a 20-min rest period and 40 min of cycling (30% of V̇o2 max). Subjects in the EM group were tested twice in the chamber: once during the follicular and once during the luteal phase. Heat production per kilogram in thermoneutrality and in the cold was significantly ( P < 0.05) higher in the PM compared with the EM girls. However, the PM girls had a significantly ( P < 0.05) lower core temperature in the cold than the EM group. PM girls also had a significantly higher body surface area-to-mass ratio compared with the EM girls. Although percent body fat between groups was not significantly different, within the PM group percent body fat explained 79% ( P < 0.01) of the variance in the decrease of core temperature. There were no menstrual phase-related differences in temperature regulation in either the thermoneutral or cold environment. In conclusion, menstrual phase does not influence temperature regulation in female individuals during adolescence. EM girls had lower metabolic heat production but maintained their core temperature more effectively in the cold than did the PM girls. This thermoregulatory difference between PM and EM girls is mainly a function of geometric differences with maturation-related peripheral vasoconstrictive differences maybe limiting the effectiveness of the mechanism of increased heat storage in younger female individuals.

Comparison of thermoregulatory responses between men and women immersed in cold water

Eleven women (age = 24.4 +/- 6.3 yr, mass = 65.0 +/- 7.8 kg, height = 167 +/- 8 cm, body fatness = 22.4 +/- 5.9%, mean +/- SD) were immersed to neck level in 18 degrees C water for up to 90 min for comparison of their thermal responses with those of men (n = 14) in a previous similarly conducted protocol. Metabolic rate increased about three times resting levels in men and women, whereas the rate of rectal temperature cooling (DeltaT(re)/Deltat) in women (0.47 degrees C/h) was about one-half that in men. With use of all data, DeltaT(re)/Deltat correlates with the ratio of body surface area to size and the metabolic rate of shivering correlates inversely to the square root of body fatness. No significant gender differences in total metabolic heat production normalized for body mass or surface area were found among subjects who completed 90 min of immersion (9 women and 7 men). Nor was there a gender difference in the overall percent contribution ( approximately 60%) of fat oxidation to total heat production. Blood concentrations of free fatty acids, glycerol, beta-hydroxybutyrate, and lactate increased significantly during the 90-min immersion, whereas muscle glycogen sampled from the right quadriceps femoris vastus lateralis decreased (free fatty acids, glycerol, and beta-hydroxybutyrate were higher in women). When the subjects were subgrouped according to similar body fatness and 60 min of immersion (6 women and 5 men), no significant gender differences emerged in DeltaT(re)/Deltat, energy metabolism, and percent fat oxidation. These findings suggest that no gender adjustments are necessary for prediction models of cold response if body fatness and the ratio of body surface area to size are taken into account and that a potential gender advantage with regard to carbohydrate sparing during cold water immersion is not supported.

Metabolic and endocrine responses to cold air in women differing in aerobic capacity

PURPOSE

The purpose of this study was to measure resting metabolic rate, plasma norepinephrine, and plasma immunoreactive beta endorphin during exposures to cold air during two consecutive 5-d periods, separated by 2 weekend days, in two groups of women differing in aerobic fitness.

METHODS

Plasma norepinephrine (NE), plasma immunoreactive beta-endorphin (IBE), and resting metabolic response (RMR) were measured during repeated exposures to 3.5 degrees C air in two groups of women differing in aerobic fitness. Ten women, separated into highly fit (HFW) and less fit (LFW) groups, sat in 22 degrees C air for 45 min followed by 45 min in 3.5 degrees C air each day during two consecutive 5-d periods separated by two weekend days.

RESULTS

Norepinephrine was not different between groups during warm air exposure; however, following 45 min of cold air, NE was two times higher in HFW compared with that in LFW (P < 0.001). Plasma IBE was elevated (P < 0.02) in HFW compared with that in LFW but was not affected by exposure to cold on any test day. Warm RMR was not different between groups and remained unchanged during the study period. Cold RMR was significantly higher in LFW compared with that in HFW (P < 0.01). Resting metabolic rate peaked at 30% of VO2peak in LFW by the 5th minute of cold exposure on day 1 before declining to 21% and remaining steady. In contrast, RMR in HFW peaked at about 13% and then fell to 9.4% before slowly increasing to 14% by the end of 45 min. On other test days HFW RMR increased to 14% of VO2peak and rose slowly through 45 min of cold exposure while LFW RMR peaked at 24% of VO2peak before declining to 20% and remaining steady.

CONCLUSIONS

Our findings suggest that, in women, aerobic fitness alters the endocrine and metabolic responses to acute cold air exposure. The norepinephrine response is exaggerated in highly fit women exposed to cold but not the metabolic response. Immunoreactive beta endorphin was not affected by exposure to cold but was elevated in highly fit women. We further conclude that the temperature threshold for acclimation to cold air by women may be higher than the air temperature used in this study.

Exercise-induced menstrual cycle changes. A functional, temporary adaptation to metabolic stress

Chronic exercise is now known to alter the menstrual cycle. Yet, we do not yet know the true incidence of menstrual cycle alterations in athletes, because good normative data do not exist and the metabolic cost of training has not been considered in many studies. Secondary amenorrhoea is not easily induced by exercise training alone but seems to require additional metabolic stressors. Induction of secondary amenorrhoea in prospective exercise studies has not occurred, although the onset of short luteal or inadequate luteal phase cycles may occur in women even when running distances are not extensive. Such menstrual cycles may cause infertility, but this is only a temporary phenomenon since pregnancy, if desired, will usually occur upon cessation of training. Exercise-related changes in the menstrual cycle can be viewed as a functionally adaptive rather than a maladaptive dysfunction. A strong case can be made that the changes in the menstrual cycle as a result of exercise are an energy conserving strategy to protect more important biological processes. This hypothesis is consistent with the theory of metabolic arrest that has been identified in lower organisms and hibernating mammals.

Thermal responses of men and women during cold-water immersion: influence of exercise intensity

The influence of exercise intensity on thermoregulation was studied in 8 men and 8 women volunteers during three levels of arm-leg exercise (level I: 700 ml oxygen (O2).min-1; level II: 1250 ml O2.min-1; level III: 1700 ml O2.min-1) for 1 h in water at 20 and 28 degrees C (Tw). For the men in Tw 28 degrees C the rectal temperature (Tre) fell 0.79 degree C (P less than 0.05) during immersion in both rest and level-I exercise. With level-II exercise a drop in Tre of 0.54 degree C (P less than 0.05) was noted, while at level-III exercise Tre did not change from the pre-immersion value. At Tw of 20 degrees C, Tre fell throughout immersion with no significant difference in final Tre observed between rest and any exercise level. For the women at rest at Tw 28 degrees C, Tre fell 0.80 degree C (P less than 0.05) below the pre-immersion value. With the two more intense levels of exercise Tre did not decrease during immersion. In Tw 20 degrees C, the women maintained higher Tre (P less than 0.05) during level-II and level-III exercise compared to rest and exercise at level I. The Tre responses were related to changes in tissue insulation (I(t)) between rest and exercise with the largest reductions in I(t) noted between rest and level-I exercise across Tw and gender. For mean and women of similar percentage body fat, decreases in Tre were greater for the women at rest and level-I exercise in Tw 20 degrees C (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)