Creatine supplementation alters the response to a graded cycle ergometer test.

To determine the effects of creatine supplementation on cardiorespiratory responses during a graded exercise test (GXT) 36 trained adults (20 male, 16 female; 21-27 years old) performed two maximal GXTs on a cycle ergometer. The first GXT was done in a nonsupplemented condition, and the second GXT was done following 7 days of ingesting either 5 g creatine monohydrate, encased in gelatin capsules, four times daily (CS, 13 male, 6 female), or the same number of glucose capsules (PL, 7 male, 10 female). CS significantly (P<0.05) improved total test time [pre-CS = 1217 (240) s, mean (std. dev.) versus post-CS = 1289 (215) s], while PL administration had no effect (P>0.05) on total test time [pre-PL= 1037 (181) s. versus post-PL= 1047 (172) s]. In addition, both oxygen consumption (VO2) and heart rate at the end of each of the first five GXT stages were significantly lower after CS, but were unchanged after PL. Moreover, the ventilatory threshold occurred at a significantly greater VO2 for CS [pre-CS = 2.2 (0.4) l x min(-1) or 66% of peak VO2 versus post-CS = 2.6 (0.5) l x min(-1) or 78% of peak Vo2; pre-PL = 2.6 (0.9) l x min(-1) or 70% peak VO2 versus post-PL = 2.6 (1.1) l x min(-1) or 68% of peak Vo2]. Neither CS nor PL had an effect on peak Vo2 [pre-CS = 3.4 (0.7) l x min(-1) versus post-CS = 3.3 (0.7) l x min(-1); pre-PL = 3.7 (1.1) l x min(-1) versus post-PL = 3.7 (1.1) l x min(-1)]. Apparently, CS can alter the contributions of the different metabolic systems during the initial stages of a GXT. Thus, the body is able to perform the sub-maximal workloads at a lower oxygen cost with a concomitant reduction in the work performed by the cardiovascular system.

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

OBJECTIVE: Thermal sensation and the physiological responses of women (follicular phase) exposed to 17 degrees 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 x time interaction as immersion continued. However, rectal temperature for all subjects remained above 35 degrees 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.

Influence of gender and menstrual cycle on a cold air tolerance test and its relationship to thermosensitivity.

This investigation evaluated the influence of gender and phase of menstrual cycle [follicular (FOL): Days 2-6) and luteal (LUT: Days 19-24)] on a cold air tolerance test (CATT: 90-min of exposure to 5 degrees C air) in 8 females (22.7 +/- 3.0 yr) and 15 males (22.3 +/- 2.9 yr). In addition, central thermosensitivity (beta; W x kg(-1) x degrees C(-1) [i.e., the slope of the relationship between the decrease in esophageal temperature (Tes) and the increase in heat production (HP)], gathered during a separate water trial in 20 degrees C water, was correlated to the change (delta) in Tes and HP across the 90 min of resting exposure during the CATT. Analysis of variance revealed no significant differences between phase of menstrual cycle or gender for HP, mean skin temperature (Tsk), and insulation; however, a main effect for time for these parameters was demonstrated. Despite these similarities, Tes differed (P < 0.05) between males and females. Additionally, no relationship was found between beta and deltaHP and deltaTes in the males and females. Also, there was no relationship between beta and thermoregulation during the CATT in these subjects. These data suggest that menstrual cycle phase did not cause a differential response in Tes, Tsk, and HP during a CATT. Furthermore, women maintained a higher Tes than men during the CATT despite similarities in HP and Tsk.

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.

Thermal and metabolic responses of women with high fat versus low fat body composition during exposure to 5 and 27 degrees C for 120 min.

BACKGROUND: Men with high fat body composition maintain higher core temperatures, and lower aerobic metabolic rates than their low fat counterparts thus, verifying the insulatory benefit of body fat. Females, on average have more body fat and less muscle mass than males, and may maintain rectal temperature (Tre) at a lower energy cost. METHODS: The present investigation dichotomized female subjects by percent fat (low fat; n = 3, LF = 19.2+/-3% vs. high fat; n = 4 HF: 29.9+/-3%) to elucidate the thermal and metabolic responses during acute exposure to 5 and 27 degrees C air for 120 min. An ANOVA was used to examine the following: 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)). For Tre, a significant fat x time interaction (p < 0.05) was demonstrated at both 5 and 27 degrees C, whereby Tre tended to be lower in the LF group than the HF group. VO2 at 5 degrees C demonstrated a main effect for time only. For I, a main effect for time was noted at 5 degrees C. Also for I, a trend (p = 0.06) toward a main effect of fat during exposure to 5 degrees C was noted while at 27 degrees C a main effect (p < 0.05) was demonstrated. RESULTS: From this data it appears that under these conditions, the HF group demonstrated higher Tre and I values than their LF counterparts that was not accompanied with a differential response with respect to aerobic metabolic rate. Thus, the impact of body composition on energy expenditure to maintain Tre differs between LF and HF males and females.

Does capsaicin affect physiologic and thermal responses of males during immersion in 22 degrees C?

BACKGROUND: Capsaicin alters thermoregulation in adult rats by producing a dose-dependent fall in body temperature and metabolism. The present investigation examined the thermal and metabolic responses in males who were fed capsaicin (CAP: 2 mg.kg(-1) body weight) vs. a placebo (PL: a maltodextrin capsule) prior to immersion in cold water. METHODS: Seven Caucasian males aged 20-28 yr were immersed in 22 degrees C twice (PL vs. CAP), for 120 min. The following were examined: metabolism (M; W.m(-2)), rectal temperature (Tre; degrees C), mean skin temperature (Tsk; degrees C), tissue insulation (I; degrees C.m(-2).W(-1) and proportion of energy derived from carbohydrate (%CHO). RESULTS: For M, Tre, I, and Tsk there was no significant differences between treatments (PL vs. CAP) when the variables were pooled jointly over time. However, significant differences across time was detected for Tre (p = 0.0003), Tsk (p = 0.0147), and M (p = 0.0036). Values for %CHO demonstrate a main effect for treatment (p = 0.0210) suggesting the CAP (46.7-/+25.9%) treatment demonstrated a decreased reliance on carbohydrate utilization for energy provision as compared to the PL (75.0+/-21.9%) treatment. Additionally, the treatment x time interaction was significant (p = 0.0096) whereby, PL differed from CAP at 5 min only. CONCLUSION: From these data it appears that while M, Tre, and Tsk differed across time, a CAP (which differentially affected percent of energy derived from carbohydrate) feeding did not differentially affect the thermal and metabolic responses of males during acute cold water immersion.

The perceptual and physiological responses of high and low fat women exposed to 5 degrees C air for 120 minutes.

The present investigation dichotomized female subjects by percentage of fat (low fat [LF] = 19.2+/-3% [n = 4] vs high fat [HF] = 29.9+/-3% [n = 4]) to elucidate the perceptual and physiological responses during acute exposure to 5 degrees C air for 120 min. Correlational analyses were used to assess the relationship between thermal sensection (TS) and differences between LF and HF groups. Significant (p < 0.01) differences existed between the groups for TS when values were pooled over time, where HF had a lower TS (5.9+/-0.6) than LF (7.9+/-0.5). Additionally, a significant (p < 0.01) main effect for time existed, where TS, when pooled over groups T5 (3.8+/-0.7) and T30 (5.4+/-0.9), was less than T60 (7.4+/-0.6), T90 (8.6+/-0.5), and T120 (9.1+/-0.4). No significant fat x time interaction was noted despite apparent perceptual differences between the groups at most of the time points. Further, the relationships between TS and percentage of fat and fat mass were either significant or exhibited strong trends toward significance at time points T5, T30, and T60. When rectal temperature (Tre) was pooled over the four time points, the fat groups differed significantly (p < 0.05); LF (-0.21+/-0.04 degrees C) exhibited a greater ATre than HF (-0.03+/-0.04 degrees C). When Tre was pooled across the fat groups, significant (p < 0.01) differences over time were detected. From these data, it appears that the modified TS scale tested may be a good marker of thermal discomfort in females exposed to the cold because perceptual differences were noted between the groups, accompanied by apparent differences in Tre between the LF and HF groups.

A submaximal treadmill test for developing target ratings of perceived exertion for outpatient cardiac rehabilitation.

For patient populations whose heart rates cannot be used to regulate exercise intensity, the Borg Rating of Perceived Exertion (RPE) Scale is the preferred way to prescribe exercise intensity. Individual perceptual variations are best quantified by measuring perceptual intensity during maximal exercise testing; however, many situations require a submaximal protocol. Here, a submaximal treadmill procedure for establishing individualized target Ratings of Perceived Exertion is described. Target ratings of exertion were developed for outpatient cardiac rehabilitation patients using the new method and compared to target Ratings of Perceived Exertion obtained using standard techniques. A total of 144 target ratings at intensities ranging from 50% to 85% VO2max were compared. Over-all, the average difference between the two methods was 0.27 units and was not significant at any intensity. Therefore, the Treadmill Slope Method appears to be a valid submaximal test for generating target Ratings of Perceived Exertion for outpatient cardiac rehabilitation patients.

Three-point method of prescribing exercise with ratings of perceived exertion is valid for cardiac patients.

It is often difficult to use heart rate to prescribe exercise for cardiac patients due to the effects of medications and procedures such as cardiac transplantation. Ratings of Perceived Exertion (RPE) is the preferred method of regulating exercise intensity in these situations. An RPE-based exercise prescription has previously depended on perceptual data from a maximal Graded Exercise Test (GXT). Recently, using 13 healthy subjects, we validated a Three-point RPE for prescribing exercise using RPE which can be used when ratings from a GXT are not available Currently, we examined the accuracy of this method for developing target RPEs for patients in Phase II cardiac rehabilitation. Such target RPEs did not differ from those obtained using standard procedures. We conclude that the Three-point Method is valid for preparing RPE-based exercise prescriptions for Phase II cardiac rehabilitation patients.

Influence of cold water immersion on heat debt and substrate utilization in males varying in body composition: a retrospective analysis.

The present article is a retrospective analysis of previously published data. This analysis examined the effect of immersion in 18, 22 and 26 degrees C cold water, on heat debt (kJ), substrate utilization [i.e., R (respiratory exchange ratio) calculated using indirect calorimetry], and aerobic metabolic rate (i.e., VO2 (oxygen consumption) 1 # min(-1)] in 24 male volunteers (20-35 years) given a preexposure meal (60.2 g carbohydrate, 12.0 g protein, and 2.8 g fat at 60 min prior to the experimental trial) and examined during 90 min of immersion to the first thoracic vertebrae. Body composition was determined via underwater densitometry. Subjects were divided with respect to high body fat (HF; 18-22%, n = 12) or low body fat (LF; 8-12%, n = 12) and randomly assigned to one of three water temperatures. Body heat debt and R did not differ between the LF or HF groups, between temperatures, or across time. Percent calories utilized indicated that for these experimental conditions the predominant substrate utilized between the LF and HF groups across time was derived from carbohydrate. In addition, VO2 was greater (p = .0004) in the LF than HF group, and the latter was greater (p = .0013) in the 18 degrees C group versus the 26 degrees C group and increased across time (p = .0001); that is, VO2 after 5 min of immersion was less than at 60 and 90 min, and values obtained after 30 min of immersion were less than those at 90 min of immersion. Based on these data, it appears that the LF group would expend more calories (308.9 vs. 199.9 kcal, respectively) and more likely derive these calories from a carbohydrate source than the HF group during 90 min of cold water immersion. It would appear beneficial to consider a feeding supplement for the low-fat individual if immersion was in a more thermal stressful environment or extended for a protracted period of time.

A thermal perception scale for use during resting exposure to cold air.

The present investigation introduces a thermal perception scale (TS) for use during protracted resting cold exposure. The scale contains categories ranging consecutively from 0, i.e., Nothing at all, to 10, i.e., Very, very cold. Eight Caucasian men were randomly exposed to ambient air in a climatically controlled environmental chamber of 8 degrees, 12 degrees, and 27 degrees C for 120 min. on 3 separate occasions and monitored for rectal temperature (Tre), mean skin temperature (Tsk), ventilation (VE), and oxygen consumption (VO2). The terminal perceptual categories were anchored for 8 subjects and a standard set of instructions was presented prior to each trial. The anchor temperature was the room air in the anteroom which was 27 degrees C, representing 0, i.e., "Nothing at all," to extend the scale so that subsequent judgments on the scale were expressed in relation to this category. In addition, the subjects were also asked to imagine the coldest that they have ever experienced and this was designed to anchor "Very, very cold." The relations between scale scores and the thermoregulatory variables were examined with a simple linear regression and coefficients of correlation and determination for each subject. High coefficients of determination between Tsk, VO2, and VE indicated that, for individual subjects, the scores on the scale were related to VE, Tsk, and VO2. High reliability coefficients for TS were also reported. In addition, the ratings and VO2 relation tended to be similar between subjects. Therefore, this scale appears to be a valid and reliable tool for measuring the perception of cold when at rest in air.

The thermogenic effect of a carbohydrate feeding during exposure to 8, 12 and 27 degrees C.

The increased metabolic heat production in humans exposed to cold stress results from an increased oxidation of both carbohydrate and fat to provide energy to sustain temperature homeostasis. Research suggests that dietary manipulations may enhance metabolic heat production, thereby delaying hypothermia. Therefore, the present investigation examined the thermogenic effect of a sequential timed feeding regime of either a carbohydrate (CHO) or a placebo beverage (PL) before and again midway through 120 min of exposure to 8, 12 and 27 degrees C in well-nourished men. The following were examined: tissue insulation (I), rectal temperature (Tre), mean skin temperature (Tsk), metabolism (M), time-weighted heat production and respiratory exchange ratio (R). Tre, delta Tre, Tsk, M, delta M, I and time-weighted heat production revealed no significant differences between treatment (PL vs CHO) at any temperature (8, 12 and 27 degrees C). However, Tre decreased (P < 0.05) as time increased at 8, 12 and 27 degrees C while M increased (P < 0.05) and I decreased (P < 0.05) at 8 and 12 degrees C. At 8 and 27 degrees C, R differed (P < 0.05) between the PL and CHO treatments. In addition, at 8 and 12 degrees C, R increased (P < 0.05) across time reflecting the feeding. From these data it appears that while substrate utilization differed between dietary treatment (8 and 27 degrees C) and across time, this feeding regime did not differentially affect M, Tre, Tsk and I during 120 min of exposure to 8, 12 and 27 degrees C.

Are beta-endorphins and thermoregulation during cold-water immersion related?

The purpose of this investigation was to determine the relationship between core temperature (Tre), tissue insulation (I), and beta-endorphins (beta-END) during immersion in cold water. To test this, 21 males were immersed to the first thoracic vertebra for 120 min in stirred water at either 18 degrees, 22 degrees, or 26 degrees C. Subjects were divided with respect to body fat [high fat (HF) = 18-22%, n = 11; low fat (LF) = 8-12%, n = 10] and randomly assigned to one of the three temperatures. Blood was drawn at 25 and 5 min (T-25 and T-5, respectively) before immersion, after 1 h of immersion, and 5 min before the completion of the second hour (T + 60 and T + 120, respectively). No significant relationship was found between delta beta-END and delta I or delta Tre. The relationship between the changes in thermoregulatory variables and delta beta-END did not differ between the HF and LF groups. Also, beta-END (adjusted for plasma volume) was lower (P < 0.05) in the HF vs. the LF group. beta-END (pg.ml-1) increased (P < 0.05) as time increased from T-25 to T + 60 and were not progressive with duration of immersion. Thus, beta-END did not increase in proportion to level of heat loss.

Does feeding regime affect physiologic and thermal responses during exposure to 8, 20, and 27 degrees C?

When the loss of body heat is accelerated by exposure to low environmental temperatures, additional substrates must be oxidized to provide energy to sustain temperature homeostasis. Therefore, the present investigation examined the relation between feeding regime [pre-experimental carbohydrate feeding (FED) vs a fast (FAST)], during 120 min of exposure to 8, 20, and 27 degrees C in well-nourished men. The following were examined: tissue insulation (I; degrees C.m2:W-1), rectal temperature (Tre; degrees C), and oxygen consumption (VO2; ml,kg-1.min-1). VO2, Tre, and I revealed no significant differences between treatments (FED vs FAST) at any temperature. At 27 degrees C, I was less (P < 0.05) than at 20 and 8 degrees C, and decreased (P < 0.05) as exposure time increased. At 8 degrees C, VO2 was higher (P < 0.5) than at 20 or 27 degrees C, and VO2 increased as time increased (P < 0.05). Tre decreased (P < 0.05) as time increased for all conditions. Respiratory exchange ration (R) differed (P < 0.05) between treatments (FED vs FAST), temperature (8 vs 20 degrees C), and across time. Values for R suggests that carbohydrate accounted for 56% and 33% of caloric utilization during the FED vs FAST conditions, respectively. At 8 vs 20 degrees C, R represented 54% vs 30% of carbohydrate utilization. Across time, R demonstrated that in both conditions (FED vs FAST) there was a decreased reliance on carbohydrate utilization for energy provision.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of body morphology and mass on thermal responses to cold water: revisited.

Seven male volunteers were divided into two groups based on body morphology and mass. The large body mass (LM) group (n = 4) was 21.2 kg heavier and 0.32 m2.kg-1 smaller in surface area-to-mass ratio (P < 0.05) than the small body mass (SM) group (n = 3). Both groups were similar in total body fat and regional skinfold thicknesses. All subjects were immersed to the first thoracic vertebrae for 120 min in stirred water at 18 degrees C. Overall, tissue insulation was similar (P > 0.05) between the SM and LM groups across time. Perceptual ratings of thermal sensation increased (P < 0.05) across time. Therefore, as cold water immersion progressed, tissue insulation was similar and thermal sensation increased (P < 0.05) in males matched for subcutaneous fat and total fat but differing in body mass and morphology.

Physiological and thermal responses of males with varying body compositions during immersion in moderately cold water.

The effect of body composition on the thermal and metabolic responses of 24 male volunteers (20 to 35 years) was examined during 90 min of moderately cold (18, 22, or 26 degrees C) water immersion to the first thoracic vertebrae. Body composition was determined via underwater densitometry. Subjects were divided with respect to body fat (high fat (HF) = 18-22%, n = 12; Low fat (LF) = 8-12%, n = 12) and randomly assigned to one of three water temperatures. Rectal temperature (degree C) after 90 min of immersion did not differ in LF and HF at 18 degrees C (35.9 vs. 36.2), 22 degrees C (36.0 vs. 36.0), and 26 degrees C (36.0 vs. 36.3). Oxygen uptake (VO2, ml-kg-1.min-1) was greater in LF than in HF in all water temperatures. Oxygen uptake at 90 min was greater for LF than HF in 18 degrees C (11.48 vs. 9.19), 22 degrees C (9.79 vs. 4.70), and 26 degrees C (6.21 vs. 5.44). Mean skin temperature in LF and HF approached water temperature within the first 5 min. Despite the thermal strain of cold water immersion, the LF subjects were able to maintain a similar Tre compared to the HF due to a significantly greater shivering thermogenesis.