N Caine

The effects of gender and menstrual phase on carbohydrate utilization during acute cold exposure.

OBJECTIVE The purpose of this study was to evaluate the effects of gender and menstrual cycle on the percent of carbohydrate (CHO) utilized during cold water immersion (20 degrees C). Previous research has suggested that males and females utilize CHO differently during submaximal exercise. This study examined whether this differential response is replicated during a submaximal elevation in metabolism, as demonstrated during thermogenesis (i.e., shivering during acute cold exposure). METHODS Male and female subjects between the ages of 18 and 30 years were recruited for this study. Female subjects underwent the experimental trial once during the follicular phase and once during the luteal phase of their menstrual cycle. Subjects were immersed to the first thoracic vertebra until esophageal temperature reached 36.5 degrees C or for a maximum preocclusion period of 40 minutes. Peripheral temperature homeostasis via cuff occlusion (right arm and left leg) took place for 10 minutes, after which the pressure cuffs were released (postocclusion) and the subjects remained in the water for an additional 10 minutes. The following variables were measured: respiratory exchange ratio, percent of CHO utilization, and oxygen consumption (Vo2). RESULTS Analysis of variance demonstrated no significant difference between genders or phases of the menstrual cycle in respiratory exchange ratio, percent CHO utilization, or Vo2 during cold water immersion. A significant difference was observed between men and women for absolute Vo2. CONCLUSIONS These data suggest that although men and women differ with respect to absolute aerobic metabolism, this distinction does not cause a differential response with respect to substrate utilization during acute cold exposure.

Thermal sensation and substrate utilization differs among low- and high-fat women exposed to 17°C water

Objective Thermal sensation and the physiological responses of women (follicular phase) exposed to 17°C immersion for 120 minutes were investigated. Methods The subjects were divided into 2 groups by percent body fat (low fat [LF] = 21%±2% [mean ± SD] vs high fat [HF] = 30%±3%). A 2-way analysis of variance was used to determine differences between the groups in metabolism, metabolism derived from carbohydrate, metabolism derived from fat, blood glucose, rectal temperature, skin temperature, and thermal sensation. Results As anticipated, pooled metabolism increased across the 120-minute immersion. Metabolism derived from carbohydrate was significantly higher in the LF than in the HF group and increased across time. Blood glucose decreased significantly across time, yet there was no group difference, suggesting that the LF group may have utilized a greater proportion of intramuscular glycogen. The HF group demonstrated a higher rectal temperature compared to their LF counterparts. Overall, rectal temperature demonstrated a group × time interaction as immersion continued. However, rectal temperature for all subjects remained above 35°C. Surprisingly, the HF group perceived significantly greater thermal discomfort than did their LF counterparts. Conclusions Since intramuscular glycogen utilization is associated with shivering thermogenesis, the suspected greater utilization of this fuel by the LF group may have contributed to less thermal discomfort than in the HF group. However, since glycogen utilization was not directly measured, this speculation cannot be validated. It is also possible that the modified thermal sensation scale we used may not be an adequate marker of thermal discomfort in females with a high percentage of body fat (28% to 35%) exposed to cold water immersion.

Thermal sensation of old vs young males at 12, 18, and 27°C for 120 min

Research in the field of aging has provided data that suggests that there are physiological changes that occur as ones biological age increases. The present investigation examined the age-related alteration and differential response between old (OLD) and young (YNG) individuals with respect to subjective thermal sensation (TS). Participants were all regularly active and of average percent body fat relative to their age. Subjects were exposed to three different temperature trials (12, 18, and 27°C) on three separate occasions (separated by 48 h) for 120 min, wearing only a bathing suit or shorts. Subjects were instructed to insert a rectal probe to monitor rectal temperature and were instrumented with four thermocouples to monitor skin temperature. Each subject rested for 30 min in a thermoneutral environment outside the environmental chamber, during which time baseline measures were taken. Following the completion of the baseline period, the subjects were wheeled into the environmental chamber. Each trial lasted 120 min or until rectal temperature was less than or equal to 35°C, at which point the subject was immediately removed from the environmental chamber. TS was assessed using both the Gagge and Modified Gagge TS scale. At the completion of each trial the subject was removed from the chamber and allowed to exercise on a cycle ergometer. Both the Gagge and Modified Gagge scale demonstrated main effects for time and trial. Neither scale exhibited significant differences between the groups or interactions relative to the experimental groups. These data suggest that when exposed to a thermal stressor OLD and YNG subjects do not demonstrate a differential response in TS during acute cold exposure.

THE INFLUENCE OF ETHNICITY ON THERMOSENSITIVITY DURING COLD WATER IMMERSION

PURPOSE This investigation evaluated the influence of ethnicity, Caucasian (CAU) vs. African American (AA), on thermosensitivity and metabolic heat production (HP) during cold water immersion (20 degrees C) in 15 CAU (22.7 +/- 2.7 yr) vs. 7 AA (21.7 +/- 2.7 yr) males. METHODS Following a 20-min baseline period (BASE), subjects were immersed in 20 degrees C water until esophageal temperature (Tes) reached 36.5 degrees C or for a maximum pre-occlusion (Pre-OCC) time of 40 min. Arm and thigh cuffs were then inflated to 180 and 220 mm Hg, respectively, for 10 min (OCC). Following release of the inflated cuffs (Post-OCC), the slope of the relationship between the decrease in Tes and the increase in HP was used to define thermosensitivity (beta). RESULTS ANOVA revealed no significant difference in thermosensitivity between CAU and AA (CAU = 3.56 +/- 1.54 vs. AA = 2.43 +/- 1.58 W.kg(-1). degrees C(-1)). No significant differences (p > 0.05) were found for Tsk (CAU = 24.2 +/- 1.1 vs. AA = 25.1 +/- 1.1 degrees C) or HP (p > 0.05; CAU = 2.5 +/- 0.8 vs. AA = 36.5 +/- 1.8 W.kg(-1)). However, a significant (p < 0.05) main effect for ethnicity for Tes was observed (CAU = 36.7 +/- 1.8 vs. AA = 36.5 +/- 1.8 degrees C). CONCLUSION These data suggest, despite a differential response in Tes between AA and CAU groups, the beta of HP during cold water immersion is similar between CAU and AA. Therefore, these data demonstrate that when faced with a cold challenge, there is a similar response in HP between CAU and AA that is accompanied by a differential response in Tes.

THE INFLUENCE OF GENDER AND MENSTRUAL PHASE ON THERMOSENSITIVITY DURING COLD WATER IMMERSION

BACKGROUND This investigation evaluated the influence of gender and phase of menstrual cycle [follicular (FOL: days 2-6) and luteal (LUT: days 19-24) phases] on thermosensitivity and metabolic heat production (HP) during cold water immersion (20 degrees C) in 10 females (22.4 +/- 2.8 yr) and 16 males (22.4 +/- 2.9 yr). METHODS Following a 20-min baseline period (BASE), subjects were immersed until esophageal temperature (Tes) reached 36.5 degrees C or for a maximum pre-occlusion (Pre-OCC) time of 40 min. An arm and thigh cuff were then inflated to 180 and 220 mmHg, respectively, for 10 min (OCC). Following release of the inflated cuffs (Post-OCC), the slope (beta) of the relationship between the decrease in Tes and the increase in HP was used to quantify thermosensitivity. RESULTS ANOVA revealed no significant difference in thermosensitivity between phases of the menstrual cycle or between men and women (FOL = -2.76, LUT = -3.05, Males = -3.24 W x kg(-1) x degrees C(-1)). A significant (p < 0.05) main effect for gender for HP, and a significant (p < 0.05) main effect for menstrual phase for mean skin temperature (Tsk) were observed. CONCLUSIONS These data suggest, despite gender differences in HP, that the thermosensitivity of HP during cold water immersion is similar between males and females and is not influenced by menstrual cycle phase. Therefore, these data indicate that when faced with a cold challenge, women respond similarly to men in both phases of their menstrual cycle.

THERMAL AND METABOLIC RESPONSES OF HIGH AND LOW FAT WOMEN TO COLD WATER IMMERSION

BACKGROUND At rest during cold exposure, the amount of body fat plays an important role in the maintenance of core temperature. High fat (HF) individuals would therefore have an advantage as compared with their low fat (LF) counterparts. Since females usually have a higher amount of body fat than males they are expected to maintain core temperature at a lower energy cost. METHODS The purpose of the present investigation was to dichotomize female subjects by percent fat (LF = 20.5 +/- 2%, n = 6 vs. HF = 30 +/- 3%, n = 6) to elucidate the thermal and metabolic responses during acute exposure to 17 degrees C water for 120 min. The following variables were measured: rectal temperature (Tre; degrees C), mean skin temperature (Tsk; degrees C), oxygen consumption (VO2; ml x kg(-1) x min(-1)), and tissue insulation (I; degrees C x m2 x W(-1)). The experiment-wise error rate was set a priori at p = 0.05. RESULTS Unexpectedly, only one of the variables demonstrated a main effect for fat (p < 0.05). Tre demonstrated a significant (p < 0.05) group by time interaction. However, Tsk and I demonstrated a main effect for time (p < 0.05). While VO2 demonstrated an increase across time, these changes were non-significant (p > 0.05). It appears that the HF group demonstrated a similar thermal (I and Tsk) and metabolic (VO2) response as compared with the LF counterparts. However, the LF groups maintained a lower Tre as compared with the HF subjects. Perhaps leaner subjects or colder water temperatures would elucidate the value of body fat in females, and demonstrate a differential response with respect to females varying in percent body fat.