Effect of physical training on peripheral sweat production

The purpose of this study was to determine the in vivo secretory activity of sweat glands from sedentary and trained subjects. Peripheral sweat production was determined using pilocarpine iontophoresis in 40 volunteers (10 sedentary men, 10 endurance-trained men, 10 sedentary women, 10 endurance-trained women). Peripheral sweat rate was significantly (P less than 0.05) greater in trained men [6.9 +/- 0.6 (SE) g.m2.min-1] and women (6.1 +/- 0.7) compared with sedentary men (3.1 +/- 0.5) and women (2.5 +/- 0.4). Furthermore, peripheral sweat rate was significantly correlated (r = 0.73) with maximal O2 uptake. The above two findings would suggest that physical training improves the secretory activity of the human sweat gland. Such a result supports previous findings that have suggested that the potentiation in sweating seen after training is achieved via a peripheral mechanism. In addition, several gender-related differences were found in the sudorific response of men and women. Specifically, women have a significantly greater sweat gland density, whereas men have a greater sweat production per gland.     

Sex differences in thermoeffector responses during exercise at fixed requirements for heat loss

To assess potential mechanisms responsible for the lower sudomotor thermosensitivity in women during exercise, we examined sex differences in sudomotor function and skin blood flow (SkBF) during exercise performed at progressive increases in the requirement for heat loss. Eight men and eight women cycled at rates of metabolic heat production of 200, 250, and 300 W/m(2) of body surface area, with each rate being performed sequentially for 30 min. The protocol was performed in a direct calorimeter to measure evaporative heat loss (EHL) and in a thermal chamber to measure local sweat rate (LSR) (ventilated capsule), SkBF (laser-Doppler), sweat gland activation (modified iodine-paper technique), and sweat gland output (SGO) on the back, chest, and forearm. Despite a similar requirement for heat loss between the sexes, significantly lower increases in EHL and LSR were observed in women (P ≤ 0.001). Sex differences in EHL and LSR were not consistently observed during the first and second exercise periods, whereas EHL (348 ± 13 vs. 307 ± 9 W/m(2)) and LSR on the back (1.61 ± 0.07 vs. 1.20 ± 0.09 mg·min(-1)·cm(-2)), chest (1.33 ± 0.06 vs. 1.08 ± 0.09 mg·min(-1)·cm(-2)), and forearm (1.53 ± 0.07 vs. 1.20 ± 0.06 mg·min(-1)·cm(-2), men vs. women) became significantly greater in men during the last exercise period (P < 0.05). At each site, differences in LSR were solely due to a greater SGO in men, as opposed to differences in sweat gland activation. In contrast, no sex differences in SkBF were observed throughout the exercise period. The present study demonstrates that sex differences in sudomotor function are only evidenced beyond a certain requirement for heat loss, solely through differences in SGO. In contrast, the lower EHL and LSR in women are not paralleled by a lower SkBF response.     

Postprandial triacylglycerol responses in simulated night and day shift: gender differences.

A number of reports suggest that shift workers have an increased risk of coronary heart disease (CHD). One contributing factor may be the consumption of meals at night with consequent altered postprandial responses. This study investigated circulating triacylglycerol (TAG), a possible risk factor for CHD, after meals during a simulated day and night shift. Twenty-five healthy participants (10 women and 15 men) were studied. They were given a pre-meal at 0800 h and a test meal at 1330 h on a simulated day shift and then an identical pre-meal at 2000 h and test meal at 0130 h, respectively, on a simulated night shift with maintained wakefulness. Blood was sampled for 9 h after the test meal for analysis of basal and postprandial plasma TAG levels. ANOVA for repeated measures indicated higher TAG in men compared with women (p < 0.0001) and higher responses at night in both genders (p = 0.027). Incremental area under the curve (IAUC) analysis indicated that men had significantly increased postprandial TAG levels at night compared with the day: (IAUC 0-540 min, mean +/- SEM) 253.29 +/- 28.73 versus 148.33 +/- 17.28 mmol/L x min, respectively, p = 0.025. In women, night and day responses (61.16 +/- 8.93 versus 34.09 +/- 7.87 mmol/L x min, respectively, p = 0.457) were not significantly different. Circulating TAG remained elevated for longer at night in the men compared with the women (p = 0.009). This study demonstrates the existence of gender and time-of-day differences in TAG responses to a meal. These raised TAG levels at night, for a prolonged time in men, may be relevant to the increased risk of CHD in shift workers.     

Sex, Lies and fMRI-Gender Differences in Neural Basis of Deception

Deception has always been a part of human communication as it helps to promote self-presentation. Although both men and women are equally prone to try to manage their appearance, their strategies, motivation and eagerness may be different. Here, we asked if lying could be influenced by gender on both the behavioral and neural levels. To test whether the hypothesized gender differences in brain activity related to deceptive responses were caused by differential socialization in men and women, we administered the Gender Identity Inventory probing the participants' subjective social sex role. In an fMRI session, participants were instructed either to lie or to tell the truth while answering a questionnaire focusing on general and personal information. Only for personal information, we found differences in neural responses during instructed deception in men and women. The women vs. men direct contrast revealed no significant differences in areas of activation, but men showed higher BOLD signal compared to women in the left middle frontal gyrus (MFG). Moreover, this effect remained unchanged when self-reported psychological gender was controlled for. Thus, our study showed that gender differences in the neural processes engaged during falsifying personal information might be independent from socialization.     

Gender differences in insulin action after a single bout of exercise.

Effects of a single exercise bout on insulin action were compared in men (n = 10) and women (n = 10). On an exercise day, subjects cycled for 90 min at 85% lactate threshold, whereas on a rest (control) day, they remained semirecumbent. The period of exercise, or rest, was followed by a 3-h hyperinsulinemic-euglycemic clamp (30 mU.m(-2).min(-1)) and indirect calorimetry. Glucose kinetics were measured isotopically by using an infusion of [6,6-2H2]glucose. Glucose infusion rate (GIR) during the clamp on the rest day was not different between the genders. However, GIR on the exercise day was significantly lower in men compared with women (P = 0.01). This was mainly due to a significantly lower glucose rate of disappearance in men compared with women (P = 0.05), whereas no differences were observed in the endogenous glucose rate of appearance. Nonprotein respiratory quotient (NPRQ) increased significantly during the clamp from preclamp measurements in men and women on the rest day (P < 0.01). Exercise abolished the increase in NPRQ seen during the clamp on the rest day and tended to decrease NPRQ in men. Our results indicate the following: 1) exercise abolishes the usual increase in NPRQ observed during a hyperinsulinemic-euglycemic clamp in both genders, 2) men exhibit relatively lower whole body insulin action in the 3-4 h after exercise compared with women, and 3) gender differences in insulin action may be explained by a lower glucose rate of disappearance in the men after acute exercise. Together, these data imply gender differences in insulin action postexercise exist in peripheral tissues and not in liver.     

Does gender influence human cardiovascular and renal responses to water immersion?

We hypothesized that women and men exhibit similar cardiovascular and renal responses to thermoneutral water immersion (WI) to the neck. Ten women and nine men underwent two sessions in random order: 1) seated nonimmersed for 5.5 h (control) and 2) WI for 3 h, with subjects seated nonimmersed for 1.5 h pre- and 1 h postimmersion. We measured left atrial diameter, heart rate, arterial pressure, urine volume and osmolality, and urinary endothelin, urodilatin, sodium, and potassium excretion. No significant difference existed between groups in cardiovascular responses. The groups also exhibited mostly similar renal responses to immersion after adjustment for body mass. However, female urodilatin excretion per kilogram during immersion was over twofold that of men, and the female kaliuretic response to immersion was delayed and less pronounced relative to that in men. Men may excrete more potassium than women during immersion because men possess greater lean body mass (potassium per kilogram). Results obtained in men during WI may be cautiously extrapolated to women, yet urodilatin and potassium responses exhibit gender differences.     

Gender Differences in Survival and the Use of Primary Care Prior to Diagnosis of Three Cancers: An Analysis of Routinely Collected UK General Practice Data

Objective

To explore whether there are gender differences in the number of GP recorded cases, the probability of survival and consulting pattern prior to diagnosis amongst patients with three non-sex-specific cancers.

Design

Cross sectional study.

Setting

UK primary care.

Subjects

12,189 patients aged 16 years or over diagnosed with colorectal cancer (CRC), 11,081 patients with lung cancer and 4,352 patients with malignant melanoma, with first record of cancer diagnosis during 1997–2006.

Main outcome measures

Cancer cases recorded in primary care; probability of survival following diagnosis; and number of GP contacts within the 24 months preceding diagnosis.

Results

From 1997–2006, overall rates of GP recorded CRC and lung cancer cases recorded were higher in men than in women, but rates of malignant melanoma were higher in women than in men. Gender differences in survival were small; 49% of men and 53% of women survived at least 5 years following CRC diagnosis; 9% of men and 12% of women with lung cancer, and 77% of men and 86% of women with malignant melanoma. The adjusted male to female relative hazard ratio of death in all patients was 1.20 (95%CI 1.13–1.30), 1.24 (95%CI 1.16–1.33) and 1.73 (95%CI 1.51–2.00) for CRC, lung cancer and malignant melanoma respectively. However, gender differences in the relative risk were much smaller amongst those who died during follow-up. For each cancer, there was little evidence of gender difference in the percentage who consulted and the number of GP contacts made within 24 months prior to diagnosis.

Conclusions

This study found that patterns of consulting prior to cancer diagnosis differed little between two genders, providing no support for the hypothesis that gender differences in survival are explained by gender differences in consultation for more serious illness, and suggests the need for a more critical view of gender and consultation.     

Gender Differences in 1-Year Clinical Characteristics and Outcomes after Stroke: Results from the China National Stroke Registry

Background

Previous reports have shown inconsistent results on clinical outcomes between women and men after stroke, and little is known about gender differences on outcomes in Chinese post-stroke patients. The aim of this study was to explore whether there were gender differences on clinical characteristics and outcomes in Chinese patients after ischemic stroke by using the data from the China National Stroke Registry (CNSR).

Methods and Findings

Out of 12,415 consecutively recruited patients with acute ischemic stroke in the CNSR from 2007 to 2008, 11,560 (93.1%) patients were followed up for 12 months. Their clinical characteristics and outcomes on death, recurrence, and dependency were recorded. The multivariate logistic regression was performed to determine whether there were gender differences in these outcomes. Women were older than men at baseline (67.9 vs. 64.0 years, P<0.001). Women had a higher mortality, recurrence rate, and dependency rate at 3, 6, and 12 months than men, but after adjusting for age, history of diabetes, pre-stroke dependency, stroke severity, in-hospital complications, and other confounders, there were no statistically significant differences in gender on mortality and recurrence rate at 3, 6, and 12 months; and dependency rate at 3, and 6 months. However, the dependency rate at 12 months remained significantly higher in women (odds ratio, 1.24; 95% confidence interval, 1.06 to 1.45).

Conclusions

There are many differences in clinical characteristics between women and men after ischemic stroke in China. Compared with men, women are more dependent at 12 months after stroke. This difference still exists after controlling the potential confounders.     

Gender alters impact of hypobaric hypoxia on adductor pollicis muscle performance.

Recently, we reported that, at similar voluntary force development during static submaximal intermittent contractions of the adductor pollicis muscle, fatigue developed more slowly in women than in men under conditions of normobaric normoxia (NN) (Acta Physiol Scand 167: 233-239, 1999). We postulated that the slower fatigue of women was due, in part, to a greater capacity for muscle oxidative phosphorylation. The present study examined whether a gender difference in adductor pollicis muscle performance also exists during acute exposure to hypobaric hypoxia (HH; 4,300-m altitude). Healthy young men (n = 12) and women (n = 21) performed repeated static contractions at 50% of maximal voluntary contraction (MVC) force of rested muscle for 5 s followed by 5 s of rest until exhaustion. MVC force was measured before and at the end of each minute of exercise and at exhaustion. Exhaustion was defined as an MVC force decline to 50% of that of rested muscle. For each gender, MVC force of rested muscle in HH was not significantly different from that in NN. MVC force tended to decline at a faster rate in HH than in NN for men but not for women. In both environments, MVC force declined faster (P < 0.01) for men than for women. For men, endurance time to exhaustion was shorter (P < 0.01) in HH than in NN [6.08 +/- 0.7 vs. 8.00 +/- 0.7 (SE) min]. However, for women, endurance time to exhaustion was similar (not significant) in HH (12.86 +/- 1.2 min) and NN (13.95 +/- 1.0 min). In both environments, endurance time to exhaustion was longer for women than for men (P < 0.01). Gender differences in the impact of HH on adductor pollicis muscle endurance persisted in a smaller number of men and women matched (n = 4 pairs) for MVC force of rested muscle and thus on submaximal absolute force and, by inference, ATP demand in both environments. In contrast to gender differences in the impact of HH on small-muscle (adductor pollicis) exercise performance, peak O(2) uptake during large-muscle exercise was lower in HH than in NN by a similar (P > 0.05) percentage for men and women (-27.6 +/- 2 and -25.1 +/- 2%, respectively). Our findings are consistent with the postulate of a higher adductor pollicis muscle oxidative capacity in women than in men and imply that isolated performance of muscle with a higher oxidative capacity may be less impaired when the muscle is exposed to HH.     

Respiratory control stability and upper airway collapsibility in men and women with obstructive sleep apnea.

Obstructive sleep apnea (OSA) is two to three times more common in men as in women. The mechanisms leading to this difference are currently unclear but could include gender differences in respiratory stability [loop gain (LG)] or upper airway collapsibility [pharyngeal critical closing pressure (Pcrit)]. The aim of this study was to compare LG and Pcrit between men and women with OSA to determine whether the factors contributing to apnea are similar between genders. The first group of 11 men and 11 women were matched for OSA severity (mean +/- SE apnea-hypopnea index = 43.8 +/- 6.1 and 44.1 +/- 6.6 events/h). The second group of 12 men and 12 women were matched for body mass index (BMI; 31.6 +/- 1.9 and 31.3 +/- 1.8 kg/m2, respectively). All measurements were made during stable supine non-rapid eye movement sleep. LG was determined using a proportional assist ventilator. Pcrit was measured by progressively dropping the continuous positive airway pressure level for three to five breaths until airway collapse. Apnea-hypopnea index-matched women had a higher BMI than men (38.0 +/- 2.4 vs. 30.0 +/- 1.9 kg/m2; P = 0.03), but LG and Pcrit were similar between men and women (LG: 0.37 +/- 0.02 and 0.37 +/- 0.02, respectively, P = 0.92; Pcrit: 0.35 +/- 0.62 and -0.18 +/- 0.87, respectively, P = 0.63). In the BMI-matched subgroup, women had less severe OSA during non-rapid eye movement sleep (30.9 +/- 7.4 vs. 52.5 +/- 8.1 events/h; P = 0.04) and lower Pcrit (-2.01 +/- 0.62 vs. 1.16 +/- 0.83 cmH2O; P = 0.005). However, LG was not significantly different between genders (0.38 +/- 0.02 vs. 0.33 +/- 0.03; P = 0.14). These results suggest that women may be protected from developing OSA by having a less collapsible upper airway for any given degree of obesity.     

Gender differences in polysomnographic sleep in young healthy sleepers

Middle-aged and elderly populations exhibit gender differences in polysomnographic (PSG) sleep; however, whether young men and women also show such differences remains unclear. Thirty-one young healthy sleepers (16 men and 15 women, aged 18 to 30 yr, mean+/-SD, 20.5+/-2.4 yr) completed 3 consecutive overnight sessions in a sleep laboratory, after maintaining a stable sleep-wake cycle for 1 wk before study entry. Standard PSG sleep and self-rated sleepiness data were collected each night. Across nights, women showed better sleep quality than men: they fell asleep faster (shorter sleep onset latency) and had better sleep efficiency, with more time asleep and less time awake (all differences showed large effect sizes, d=0.98 to 1.12). By contrast, men were sleepier than women across nights. Both men and women demonstrated poorer overall sleep quality on the first night compared with the subsequent 2 nights of study. We conclude young adult healthy sleepers show robust gender differences in PSG sleep, like older populations, with better sleep quality in women than in men. These results highlight the importance of gender in sleep and circadian rhythm research studies employing young subjects and have broader implications for women's health issues relating to these topics.     

Effect of gender on vestibular sympathoexcitation

Studies have suggested that premenopausal women are more prone to orthostatic intolerance than men. Additionally, it has been postulated that the vestibulosympathetic reflex is important in regulating postural-related changes in sympathetic activity. The purpose of the present study was to determine whether men and women differ in their sympathetic and cardiovascular responses to stimulation of the otolith organs elicited by head-down rotation (HDR). Heart rate (HR), arterial pressure, calf blood flow (CBF), and leg muscle sympathetic nerve activity (MSNA) were measured during 3 min of HDR in the prone posture in 33 women and 30 men. With the exception of HR (71 +/- 2 and 63 +/- 1 beats/min for women and men, respectively; P < 0.01), all baseline variables were not different between genders. There were no gender differences in responses to HDR. MSNA increased 72 +/- 33 units (43%) in the men and 88 +/- 15 units (59%) in the women during HDR (P < 0.01). CBF decreased [-0.6 +/- 0.1 (15%) and -0.5 +/- 0.1 (19%) ml. min(-1). 100 ml(-1)] and calf vascular resistance increased [8 +/- 2 (21%) and 11 +/- 3 (25%) units during HDR for men and women, respectively (P < 0.01)]. Both in the men and women, HR increased 2 +/- 1 beats/min (P < 0.01). These results demonstrate that sympathetic activation during HDR in the prone posture is similar in men and women. Therefore, these findings suggest that the vestibulosympathetic reflex is not different between healthy men and women.     

Gender difference in C-reactive protein concentrations in individuals with atherothrombotic risk factors and apparently healthy ones.

Recent studies have shown that C-reactive proteins have a pathogenetic role in atherothrombosis and concentrations of these substances could be used as a marker for future vascular events. The objective of this study was to determine gender differences in highly sensitive C-reactive protein (hs-CRP) in individuals with atherothrombotic risk factors and apparently healthy ones. We have presently matched 469 females and 469 males having the same age and body mass index (BMI). Of these, 210 men and 210 women had no atherothrombotic risk factors. In this group the hs-CRP concentrations were 1.6+/-3.4 mg l(-1) in women and 1.0+/-2.7 mg l(-1) in men (p<0.0005). These values were 2.1+/-3.4 mg l(-1) and 1.5+/-2.8 mg l(-1), respectively, in the entire cohort (p<0.0005), which included also individuals with atherothrombotic risk factors. We conclude that significant gender differences exist in hs-CRP concentrations despite perfect matching for age and BMI. These differences should be reflected in guidelines that suggest hs-CRP cut-off points for the stratification of vascular risk.     

Relative health effects of education, socioeconomic status and domestic gender inequity in Sweden: a cohort study

Introduction

Limited existing research on gender inequities suggests that for men workplace atmosphere shapes wellbeing while women are less susceptible to socioeconomic or work status but vulnerable to home inequities.

Methods

Using the 2007 Northern Swedish Cohort (n = 773) we identified relative contributions of perceived gender inequities in relationships, financial strain, and education to self-reported health to determine whether controlling for sex, examining interactions between sex and other social variables, or sex-disaggregating data yielded most information about sex differences.

Results and Discussion

Men had lower education but also less financial strain, and experienced less gender inequity. Overall, low education and financial strain detracted from health. However, sex-disaggregated data showed this to be true for women, whereas for men only gender inequity at home affected health. In the relatively egalitarian Swedish environment where women more readily enter all work arenas and men often provide parenting, traditional primacy of the home environment (for women) and the work environment (for men) in shaping health is reversing such that perceived domestic gender inequity has a significant health impact on men, while for women only education and financial strain are contributory. These outcomes were identified only when data were sex-disaggregated.     

Effect of morning exercise on counterregulatory responses to subsequent, afternoon exercise.

The aim of this study was to determine whether a bout of morning exercise (EXE(1)) can alter neuroendocrine and metabolic responses to subsequent afternoon exercise (EXE(2)) and whether these changes follow a gender-specific pattern. Sixteen healthy volunteers (8 men and 8 women, age 27 +/- 1 yr, body mass index 23 +/- 1 kg/m(2), maximal O(2) uptake 31 +/- 2 ml x kg(-1) x min(-1)) were studied after an overnight fast. EXE(1) and EXE(2) each consisted of 90 min of cycling on a stationary bike at 48 +/- 2% of maximal O(2) uptake separated by 3 h. To avoid the confounding effects of hypoglycemia and glycogen depletion, carbohydrate (1.5 g/kg body wt po) was given after EXE(1), and plasma glucose was maintained at euglycemia during both episodes of exercise by a modification of the glucose-clamp technique. Basal insulin levels (7 +/- 1 microU/ml) and exercise-induced insulin decreases (-3 microU/ml) were similar during EXE(1) and EXE(2). Plasma glucose was 5.2 +/- 0.1 and 5.2 +/- 0.1 mmol/l during EXE(1) and EXE(2), respectively. The glucose infusion rate needed to maintain euglycemia during the last 30 min of exercise was increased during EXE(2) compared with EXE(1) (32 +/- 4 vs. 7 +/- 2 micromol x kg(-1) x min(-1)). Although this increased need for exogenous glucose was similar in men and women, gender differences in counterregulatory responses were significant. Compared with EXE(1), epinephrine, norepinephrine, growth hormone, pancreatic polypeptide, and cortisol responses were blunted during EXE(2) in men, but neuroendocrine responses were preserved or increased in women. In summary, morning exercise significantly impaired the body's ability to maintain euglycemia during later exercise of similar intensity and duration. We conclude that antecedent exercise can significantly modify, in a gender-specific fashion, metabolic and neuroendocrine responses to subsequent exercise.     

Gender differences in skeletal muscle fatigability are related to contraction type and EMG spectral compression.

The purposes of this study were 1) to evaluate gender differences in back extensor endurance capacity during isometric and isotonic muscular contractions, 2) to determine the relation between absolute load and endurance time, and 3) to compare men [n = 10, age 22.4 +/- 0.69 (SE) yr] and women (n = 10, age 21.7 +/- 1.07 yr) in terms of neuromuscular activation patterns and median frequency (MF) shifts in the electromyogram (EMG) power spectrum of the lumbar and hip extensor muscles during fatiguing submaximal isometric trunk extension exercise. Subjects performed isotonic and isometric trunk extension exercise to muscular failure at 50% of maximum voluntary contraction force. Women exhibited a longer endurance time than men during the isometric task (146.0 +/- 10.9 vs. 105.4 +/- 7.9 s), but there was no difference in endurance performance during the isotonic exercise (24.3 +/- 3.4 vs. 24.0 +/- 2.8 repetitions). Absolute load was significantly related to isometric endurance time in the pooled sample (R(2) = 0.34) but not when men and women were analyzed separately (R(2) = 0.05 and 0.04, respectively). EMG data showed no differences in neuromuscular activation patterns; however, gender differences in MF shifts were observed. Women demonstrated a similar fatigability in the biceps femoris and lumbar extensors, whereas in men, the fatigability was more pronounced in the lumbar musculature than in the biceps femoris. Additionally, the MF of the lumbar extensors demonstrated a greater association with endurance time in men than in women (R(2) = 0.45 vs. 0.19). These findings suggest that gender differences in muscle fatigue are influenced by muscle contraction type and frequency shifts in the EMG signal but not by alterations in the synergistic activation patterns.     

The determinants of fracture in men

Osteoporosis represents an increasingly important clinical and public health problem among older men. Estimates indicated that 1-2 million (3-6%) men aged 50 years and over in the United States have osteoporosis and 8-13 million (28- 47%) have osteopenia. The lifetime risk of suffering a hip, spine or forearm fracture for a 50-year-old man is 13%, similar to the risk for prostate cancer. The number of osteoporotic fractures in men is expected to increase dramatically due to aging of the population and secular increases in fracture rates. Identification of men who are at greatest risk of osteoporosis and the risk factors, which predispose men to fracture, are essential so that preventive steps can be taken. Data on risk factors are emerging but many questions remain. Men may fracture at a higher bone mineral density (BMD) level than women. However, estimates of volumetric BMD, which correct in part for gender differences in bone size, and risk of fracture, may actually show similar relationships in men and women. Fracture rates are similar in older African American women and Caucasian men. Improved understanding of ethnic differences in fracture could identify potential reasons for gender differences. Family history and genetic factors are also important risk factors for fractures but the specific candidate genes are not known and whether gender modifies the effects of these genetic polymorphisms on BMD and the risk of fracture is also not known. In general, lifestyle factors and anthropometric measurements show similar relationships with fractures in men and women although few comprehensive prospective studies have been conducted. Current data will be reviewed on the relationships between markers of skeletal health, genetic polymorphisms, lifestyle and anthropometric factors and fracture.     

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.     

Hypohydration and exercise: effects of heat acclimation, gender, and environment

This study examined the effects of heat acclimation and subject gender on treadmill exercise in comfortable (20 degrees C, 40% rh), hot-dry (49 degrees C, 20% rh), and hot-wet (35 degrees C, 79% rh) environments while subjects were hypo- or euhydrated. Six male and six female subjects, matched for maximal aerobic power and percent body fat, completed two exercise tests in each environment both before and after a 10-day heat acclimation program. One exercise test was completed during euhydration and one during hypohydration (-5.0% from baseline body weight). In general, no significant (P greater than 0.05) differences were noted between men and women at the completion of exercise for rectal temperature (Tre), mean skin temperature (Tsk), or heat rate (HR) during any of the experimental conditions. Hypohydration generally increased Tre and HR values and decreased sweat rate values while not altering Tsk values. In the hypohydration experiments, heat acclimation significantly reduced Tre (0.19 degrees C) and HR (13 beats X min-1) values in the comfortable environment, but only HR values were reduced in hot-dry (21 beats X min-1) and hot-wet (21 beats X min-1) environments. The present findings indicated that men and women respond in a physiologically similar manner to hypohydration during exercise. They also indicated that for hypohydrated subjects heat acclimation decreased thermoregulatory and cardiovascular strain in a comfortable environment, but only cardiovascular strain decreased in hot environments.