A Single Dose of Ibuprofen Impacts IL-10 Response to 164-km Road Cycling in the Heat

Purpose: The purpose was to determine the effect of a single-dose prophylactic ibuprofen use before a 164-km road cycling event in high ambient temperature on the circulating cytokine and leukocyte responses. Methods: Twenty-three men (53 ± 8 y, 172.0 ± 22.0 cm, 85.1 ± 12.8 kg, 19.6 ± 4.4% body fat) completed a 164-km self-paced recreational road cycling event in a hot, humid, sunny environment (WBGT = 29.0 ± 2.9°C) after consuming 600 mg of ibuprofen (n = 13) or a placebo (n = 10). Blood samples were obtained one to two hours before (PRE) and immediately after (POST) the event, and analyzed for concentrations of circulating cytokines interleukins (IL)-1β, IL-2, IL-4, IL-5, IL-6, IL-7, IL-8, IL-10, IL-12, IL-13, GM-CSF, IFN-γ, and TNF-α and leukocytes (total leukocytes, granulocytes, monocytes, and lymphocytes). Results: Event completion time was 400.2 ± 74.8 min. Concentrations of all cytokines (except IL-1β, IL-2, IL-5, IL-12, GM-CSF, and IFN-γ) and of all leukocyte subsets increased from PRE to POST. Ibuprofen ingestion attenuated the increase in IL-10 (86% increase with Ibuprofen; 270% increase with placebo). Conclusions: Consuming 600 mg of Ibuprofen prior to a 164-km road cycling event in a hot-humid environment attenuates exercise-induced increases in the concentration of the anti-inflammatory cytokine IL-10, but does not alter the effect of the exercise event on concentrations of other circulating cytokines or leukocyte subset concentrations.

Direct and Indirect Effects of Fibroblast Growth Factor (FGF) 15 and FGF19 on Liver Fibrosis Development

Farnesoid X receptor (FXR) induces fibroblast growth factor 15 (FGF15; human ortholog FGF19) in the gut to potently inhibit bile acid (BA) synthesis in the liver. FXR activation in hepatic stellate cells (HSCs) reduces liver fibrosis (LF). Fgf15^-/- mice develop attenuated LF, but the underlying mechanisms for this protection are unclear. We hypothesized that FGF15/19 functions as a profibrotic mediator or mitogen to HSCs and increased BAs in Fgf15^-/- mice leads to enhanced FXR activation in HSCs, subsequently reducing fibrogenesis. In this study, complimentary in vivo and in vitro approaches were used: (1) CCl₄ -induced LF model in wild type (WT), Fgf15^-/- , and Fgf15 transgenic (TG) mice with BA levels modulated by feeding cholestyramine- or cholic acid-containing diets; (2) analysis of primary HSCs isolated from WT and Fgf15^-/- mice; and (3) treatment of a human HSC line, LX-2, with FXR activators and/or recombinant FGF19 protein. The results showed that Fgf15^-/- mice had lower basal collagen expression, which was increased by BA sequestration. CCl₄ induced fibrosis with similar severity in all genotypes; however, cholestyramine increased fibrosis severity only in Fgf15^-/- mice. HSCs from Fgf15^-/- mice showed increased FXR activity and reduced expression of profibrotic mediators. In LX-2 cells, FXR activation increased peroxisome proliferator-activated receptor gamma activity and reduced proliferation. FGF19 activated both signal transducer and activator of transcription 3 and c-Jun N-terminal kinase pathways and reduced nuclear factor kappa-light-chain-enhancer of activated B cells signaling without increasing fibrogenic gene expression or cell proliferation. Conclusion: FGF15/19 does not act as a direct profibrotic mediator or mitogen to HSCs in our models, and the protection against fibrosis by FGF15 deficiency may be mediated through increased BA activation of FXR in HSCs.

Weight bias among exercise and nutrition professionals: a systematic review

Obesity affects approximately one-third of American adults. Recent evidence suggests that weight bias may be pervasive among both exercise and nutrition professionals working with adults who have obesity. However, the published literature on this topic is limited. This review aimed to (i) systematically review existing literature examining weight bias among exercise and nutrition professionals; (ii) discuss the implications of this evidence for exercise and nutrition professionals and their clients; (iii) address gaps and limitations of this literature; and (iv) identify future research directions. Of the 31 studies that met the criteria for this review, 20 examined weight bias among exercise professionals, of which 17 (85%) found evidence of weight bias among professionals practicing physical therapy (n = 4), physical education (n = 8) and personal/group fitness training (n = 5). Of 11 studies examining weight bias among nutrition professionals, eight (73%) found evidence of weight bias. These findings demonstrate fairly consistent evidence of weight bias among exercise and nutrition professionals. However, the majority of studies were cross-sectional (90%). Given that weight bias may compromise quality of care and potentially reinforce weight gain and associated negative health consequences in patients with obesity, it is imperative for future work to examine the causes and consequences of weight bias within exercise and nutrition professions using more rigorous study designs.

Factors Associated with Pre-Event Hydration Status and Drinking Behavior of Middle-Aged Cyclists

OBJECTIVES

Water is an essential nutrient for thermoregulation, metabolism, cognition, and overall physiological homeostatic function. However, aging adults display a blunted thirst mechanism and subsequently have an increased risk for dehydration or hyponatremia. Fluid consumption behaviors are modifiable and the importance of practicing adequate drinking behaviors for aging adults is amplified during exercise. Identification of aging adult's hydration beliefs and how they attain hydration advice could provide valuable information into ways to promote better drinking habits to reduce fluid imbalances. Thus, this investigation evaluated the knowledge, beliefs and behaviors of middle-aged cyclists (MA) that were associated with hydration status and drinking behavior, before and during a 164-km mass-participation event (ambient temperature, 33.3±2.8ºC(mean±SD)).

DESIGN

This cross-sectional field study retrospectively grouped participants by their second urine specific gravity (Usg) measurement of the event morning prior to a mass participation cycling event. Usg was assessed via handheld refractometer.

SETTING

The Hotter N' Hell Hundred 164-km cycling event in Wichita Falls, Texas during the month of August.

PARTICIPANTS

36 male recreational cyclists (age, 53±9 y(mean±SD)).

MEASUREMENTS

Participants were grouped according their urine specific gravity as either slightly hyperhydrated (SH; n=12, Usg≤1.014), euhydrated (EUH; n=12, Usg, 1.015-1.020), or slightly dehydrated (SD; n=12, Usg≥1.021). Exercise histories and questionnaires were recorded 24-48 h prior to the cycling event.

RESULTS

Regardless of pre-event hydration status, all groups experienced a similar body mass loss during the 164-km event and finished with statistically similar exercise times; also, drinking behavior within all groups was influenced by multiple factors. The primary factors associated with MA cyclist drinking behavior were trial and error/personal history and thirst; further, the majority of cyclists (≥65%) in SH, EUH, and SD believed that dehydration affects performance negatively. The least important factors included rehydration recommendations from scientific and sports medicine organizations, plus information from sports drink manufacturers.

CONCLUSION

Considering the complexity of the present findings and the physiological changes that accompany aging such as delayed thirst perception, we recommend that MA cyclists formulate an individualized drinking plan that is based on observations during exercise.

Relation between urinary hydration biomarkers and total fluid intake in healthy adults

BACKGROUND/OBJECTIVES

In sedentary adults, hydration is mostly influenced by total fluid intake and not by sweat losses; moreover, low daily fluid intake is associated with adverse health outcomes. This study aimed to model the relation between total fluid intake and urinary hydration biomarkers.

SUBJECTS/METHODS

During 4 consecutive weekdays, 82 adults (age, 31.6±4.3 years; body mass index, 23.2±2.7 kg/m(2); 52% female) recorded food and fluid consumed, collected one first morning urine (FMU) void and three 24-h (24hU) samples. The strength of linear association between urinary hydration biomarkers and fluid intake volume was evaluated using simple linear regression and Pearson's correlation. Multivariate partial least squares (PLS) modeled the association between fluid intake and 24hU hydration biomarkers.

RESULTS

Strong associations (|r| &#8805; 0.6; P<0.001) were found between total fluid intake volume and 24hU osmolality, color, specific gravity (USG), volume and solute concentrations. Many 24hU biomarkers were collinear (osmolality versus color: r=0.49-0.76; USG versus color: r=0.46-0.78; osmolality versus USG: 0.86-0.97; P<0.001). Measures in FMU were not strongly correlated to intake. Multivariate PLS and simple linear regression using urine volume explained >50% of the variance in fluid intake volume (r(2)=0.59 and 0.52, respectively); however the error in both models was high and the limits of agreement very large.

CONCLUSIONS

Hydration biomarkers in 24hU are strongly correlated with daily total fluid intake volume in sedentary adults in free-living conditions; however, the margin of error in the present models limits the applicability of estimating fluid intake from urinary biomarkers.

Interpreting common hydration biomarkers on the basis of solute and water excretion

BACKGROUND/OBJECTIVES

This investigation evaluated 12 hydration biomarkers, to determine which represent 24-h whole-body water balance (that is, measured as water retention or clearance (WR-C) by the kidneys).

SUBJECTS/METHODS

Healthy males (n=59; body mass, 75.1±7.9 kg; height, 178±6 cm; age, 22±3 years; body mass index, 23.9±2.4 kg/m(2)) met with a registered dietitian each morning (days 1-11) to optimize completeness and accuracy of food and fluid records, then went about ordinary daily activities. These men visited the laboratory for blood samples and collected all urine produced on days 1, 3, 6, 9 and 12. The reference standard (WR-C) was calculated using 24-h urine volume, 24-h urine osmolality, and serum osmolality (single morning venous sample).

RESULTS

Statistical regression analyses indicated that, among the 12 hydration biomarkers, only 24-h urine osmolality (r(2)=0.60, P<0.0001) and 24-h urine specific gravity (r(2)=0.52, P<0.0001) strongly predicted WR-C. The 24-h fluid intake, 24-h body mass change, 24-h urine color and 24-h urine volume were weak (P>0.05) predictors of WR-C, similar to serum osmolality and other single measurements (range of r(2) values, 0.19-0.0001).

CONCLUSIONS

These observations of healthy, active young men demonstrate that WR-C is strongly related to the 24-h concentration of urine, which in turn reflects the excretion of total solids in the diet. Although morning urine assessments provided information about a single time point, 24-h urine osmolality and 24-h urine specific gravity were the best predictors of 24-h body water balance.

Recommendations for healthier hydration: addressing the public health issues of obesity and type 2 diabetes

Given the rapid increase in the prevalence of overweight, obesity, type 2 diabetes and other obesity-related conditions across the world, despite a plethora of evidence-based guidance for clinicians, innovative campaigns aimed at the general public and widespread government public health initiatives, it is clear that a novel approach is required. The importance of fluid intake has been overlooked in campaigns and guidelines and also in the clinical setting, where the question 'what do you drink?' is often omitted. It is a significant oversight that food pyramids and healthy-eating plates across the world omit fluids from their graphics and advice. While guidelines include recommendations on changes in physical activity and diet, often little or no advice is offered on the importance of healthier hydration practices, neglecting to highlight the contribution of beverages high in sugar, alcohol or additives. An interdisciplinary group of experts in medicine, nutrition, physiology and public health discussed issues surrounding healthy-hydration practices in March 2010 in Paris to create a consensus statement on hydration and gain of body weight and provide recommendations.

Rehydration with fluid of varying tonicities: effects on fluid regulatory hormones and exercise performance in the heat

This study examined the effects of rehydration (Rehy) with fluids of varying tonicities and routes of administration after exercise-induced hypohydration on exercise performance, fluid regulatory hormone responses, and cardiovascular and thermoregulatory strain during subsequent exercise in the heat. On four occasions, eight men performed an exercise-dehydration protocol of ∼185 min (33°C) to establish a 4% reduction in body weight. Following dehydration, 2% of the fluid lost was replaced during the first 45 min of a 100-min rest period by one of three random Rehy treatments (0.9% saline intravenous; 0.45% saline intravenous; 0.45% saline oral) or no Rehy (no fluid) treatment. Subjects then stood for 20 min at 36°C and then walked at 50% maximal oxygen consumption for 90 min. Subsequent to dehydration, plasma Na+, osmolality, aldosterone, and arginine vasopressin concentrations were elevated ( P < 0.05) in each trial, accompanied by a −4% hemoconcentration. Following Rehy, there were no differences ( P > 0.05) in fluid volume restored, post-rehydration (Post-Rehy) body weight, or urine volume. Percent change in plasma volume was 5% above pre-Rehy values, and plasma Na+, osmolality, and fluid regulatory hormones were lower compared with no fluid. During exercise, skin and core temperatures, heart rate, and exercise time were not different ( P > 0.05) among the Rehy treatments. Plasma osmolality, Na+, percent change in plasma volume, and fluid regulatory hormones responded similarly among all Rehy treatments. Neither a fluid of greater tonicity nor the route of administration resulted in a more rapid or greater fluid retention, nor did it enhance heat tolerance or diminish physiological strain during subsequent exercise in the heat.

Effect of hydration state on testosterone and cortisol responses to training-intensity exercise in collegiate runners

Exercise intensity powerfully influences testosterone, cortisol, and testosterone : cortisol ratio (T:C) responses to endurance exercise. Hydration state may also modulate these hormones, and therefore may alter the anabolic/catabolic balance in response to endurance exercise and training. This study examined the effect of running intensity on testosterone, cortisol, and T : C when exercise was initiated in a hypohydrated state. Nine male collegiate runners (age = 20 +/- 0 y, height = 178 +/- 2 cm, mass = 67.0 +/- 1.8 kg, body fat % = 9.8 +/- 0.7 %, V.O2max = 65.7 +/- 1.1 ml.kg (-1).min (-1)) completed four 10-min treadmill runs differing in pre-exercise hydration status (euhydrated, or hypohydrated by 5 % of body mass) and exercise intensity (70 % or 85 % V.O2max). Body mass, urine osmolality, and urine-specific gravity documented fluid balance; blood samples drawn pre-, immediately post-, and 20 min post-exercise were analyzed for testosterone, cortisol, and T : C. Except for heart rate measured during the 70 % V.O2max trials, heart rate, V.O2, and plasma lactate were similar between euhydrated and hypohydrated conditions for a given intensity, suggesting hypohydration did not measurably increase the physiological stress of the exercise bouts. Furthermore, hydration state had no measurable effect on testosterone concentrations before, during, or after exercise at either intensity. Regardless of exercise intensity, cortisol concentrations were greater during hypohydration than euhydration pre-exercise and 20 min post-exercise. Additionally, T : C was significantly lower 20 min post-exercise at 70 % V.O2max when subjects were initially hypohydrated (T : C = 0.055) versus euhydrated (T : C = 0.072). These findings suggest that depending on exercise intensity, T : C may be altered by hydration state, therefore influencing the balance between anabolism and catabolism in response to running exercise performed at typical training intensities.

Effect of hydration status on thirst, drinking, and related hormonal responses during low-intensity exercise in the heat

During exercise-heat stress, ad libitum drinking frequently fails to match sweat output, resulting in deleterious changes in hormonal, circulatory, thermoregulatory, and psychological status. This condition, known as voluntary dehydration, is largely based on perceived thirst. To examine the role of preexercise dehydration on thirst and drinking during exercise-heat stress, 10 healthy men (21 ± 1 yr, 57 ± 1 ml·kg−1·min−1 maximal aerobic power) performed four randomized walking trials (90 min, 5.6 km/h, 5% grade) in the heat (33°C, 56% relative humidity). Trials differed in preexercise hydration status [euhydrated (Eu) or hypohydrated to −3.8 ± 0.2% baseline body weight (Hy)] and water intake during exercise [no water (NW) or water ad libitum (W)]. Blood samples taken preexercise and immediately postexercise were analyzed for hematocrit, hemoglobin, serum aldosterone, plasma osmolality (Posm), plasma vasopressin (PAVP), and plasma renin activity (PRA). Thirst was evaluated at similar times using a subjective nine-point scale. Subjects were thirstier before (6.65 ± 0.65) and drank more during Hy+W (1.65 ± 0.18 liters) than Eu+W (1.59 ± 0.41 and 0.31 ± 0.11 liters, respectively). Postexercise measures of Posm and PAVP were significantly greater during Hy+NW and plasma volume lower [Hy+NW = −5.5 ± 1.4% vs. Hy+W = +1.0 ± 2.5% ( P = 0.059), Eu+NW = −0.7 ± 0.6% ( P < 0.05), Eu+W = +0.5 ± 1.6% ( P < 0.05)] than all other trials. Except for thirst and drinking, however, no Hy+W values differed from Eu+NW or Eu+W values. In conclusion, dehydration preceding low-intensity exercise in the heat magnifies thirst-driven drinking during exercise-heat stress. Such changes result in similar fluid regulatory hormonal responses and comparable modifications in plasma volume regardless of preexercise hydration state.

Effect of overhydration on time-trial swim performance

The effect of hydration status on performance has not been adequately emphasized or examined in swimmers. Theoretically, moderate overhydration might reduce the proportionate fluid loss from the circulation during exercise of this nature. To explore this issue, 11 (5 women, 6 men) collegiate swimmers swam 2 183-m (200-yd) time trials (3 days apart) in alternate, randomized euhydrated (EUH) and overhydrated (OH) states. Pre-exercise plasma osmolality (EUH: 288.5 +/- 2.5 and OH: 284.6 +/- 3.3 mOsmol.kg(-1); p < 0.001), urine specific gravity (EUH: 1.022 +/- 0.003 and OH: 1.012 +/- 0.003; p < 0.001), and body weight (EUH: 72.1 +/- 9.3 and OH: 72.6 +/- 9.2 kg; p < 0.01) values distinguished the two hydration states of the swimmers. There was no difference (p > 0.05) between hydration states in postexercise plasma osmolality (EUH: 312.8 +/- 4.8 and OH: 307.2 +/- 9.9 mOsmol.kg(-1)), plasma volume (EUH: -16.5 +/- 10.0 and OH: -17.7 +/- 6.8 %Delta), plasma lactate (EUH: 18.6 +/- 3.6 and OH: 17.8 +/- 3.4 mmol.1(-1)), heart rate (EUH: 167 +/- 11 and OH: 166 +/- 16 beats.min(-1)), or perceived exertion (EUH: 16 +/- 1 and OH: 16 +/- 2) responses. Although performance time improved for 7 of the 11 swimmers during OH, there was not a statistically significant difference between the EUH (121.2 +/- 8.1 seconds) and OH (120.8 +/- 7.7 seconds) conditions. However, there was a modest bivariate correlation (r = -0.602; p < 0.05) between the change in body weight and change in performance time in going from the EUH to OH trials. These data demonstrated that overhydration provided no performance advantage for this group during a 183-m time-trial swim but emphasized the importance of adequate hydration in swim performance.

Perceptual responses in the heat after brief intravenous versus oral rehydration

PURPOSE

The purpose of the study was to compare the effects of a brief period (20 min) of intravenous (IV) fluid rehydration and oral (ORAL) rehydration on ratings of perceived exertion (RPE), thirst, and thermal sensation (TS) during exercise in the heat.

METHODS

After dehydration (-4% of body weight), eight nonacclimated highly trained cyclists (age = 24 +/- 1 yr; VO2 = 61.4 +/- 0.8 mL.kg.min-1) performed three experimental trials. Rehydration (randomized, cross-over design) included: 1) ORAL (0.45% NaCl) equal to 50% of prior dehydration; 2) IV (0.45% NaCl) equal to 50% of prior dehydration; and 3) a control (CON), no fluid trial. Subjects then cycled at 74% VO2peak until volitional exhaustion in a hot environment (37 degrees C).

RESULTS

Central (C-), local (L-), and overall-RPE (O-RPE) were significantly higher in CON compared to ORAL and IV at minutes 5 and 15 of exercise. C-RPE responses at minute 5 of exercise were lower (P < 0.05) during ORAL compared with IV, and C-RPE and O-RPE responses at minute 15 were lower (P < 0.05) during ORAL compared with IV. TS responses during CON were higher (P < 0.05) than ORAL and IV at minute 5, and TS was higher (P < 0.05) during IV versus ORAL at minute 15. TS were significantly correlated with all RPE responses at minute 15 in all trials. Thirst ratings were lower (P < 0.05) during ORAL compared with CON and IV at minutes 0, 5, and 15.

CONCLUSION

It was concluded that ORAL resulted in lower RPE, thirst, and TS compared with CON and IV during exercise in the heat.

Blood glucose responses to carbohydrate feeding prior to exercise in the heat: effects of hypohydration and rehydration

This study assessed the plasma glucose (PG) and hormonal responses to carbohydrate ingestion, prior to exercise in the heat, in a hypohydrated state versus partial rehydration with intravenous solutions. On separate days, 8 subjects (21.0 +/- 1.8 years; 57.3 +/- 3.7 ml x kg(-1) x min(-1)) exercised at 50% VO2max in a 33 degree C environment until a 4% body weight loss was achieved. Following this, subjects were rehydrated (25 ml x kg(-1)) with either: 0.45% IV saline (45IV), 0.9% IV saline (9IV), or no fluid (NF). Subjects then ingested 1 g x kg(-1) of carbohydrate and underwent an exercise test (treadmill walking, 50% VO2max, 36 degrees C) for up to 90 min. Compared to pre-exercise level (294 mg x dl(-1)), PG increased significantly (>124 mg x dl(-1)) at 15 min of the exercise test in all trials and remained significantly elevated for 75 min in NF, 30 min more than in the 2 rehydration trials. Although serum Insulin increased significantly at 15 min of exercise in the 45IV trial (7.2 +/- 1.2 vs. 23.7 +/- 4.7 mIU x ml(-1)), no significant differences between trials were observed. Peak plasma norepinephrine was significantly higher in NF (640 +/- 66 pg x ml(-1)) compared to the 45IV and 9IV trials (472 +/- 55 and 474 +/- 52 pg x ml(-1), respectively). In conclusion, ingestion of a small solid carbohydrate load prior to exercise in the 4% hypohydration level resulted in prolonged high PG concentration compared to partial IV rehydration.

Cortisol and testosterone concentrations in wheelchair athletes during submaximal wheelchair ergometry

It is yet unknown how upper body exercise combined with high ambient temperatures affects plasma testosterone and cortisol concentrations and furthermore, how these hormones respond to exercise in people suffering spinal cord injuries. The purpose of this study was to characterize plasma testosterone and cortisol responses to upper body exercise in wheelchair athletes (WA) compared to able-bodied individuals (AB) at two ambient temperatures. Four WA [mean age 36 (SEM 13) years, mean body mass 66.9 (SEM 11.8) kg, injury level T7-T11], matched with five AB [mean age 33.4 (SEM 8.9) years, mean body mass 72.5 (SEM 13.1) kg] exercised (cross-over design) for 20 min on a wheelchair ergometer (0.03 kg resistance.kg-1 body mass) at 25 degrees C and 32 degrees C. Blood samples were obtained before (PRE), at min 10 (MID), and min 20 (END) of exercise. No differences were found between results obtained at 25 degrees C and 32 degrees C for any physiological variable studied and therefore these data were combined. Pre-exercise testosterone concentration was lower (P < 0.05) in WA [18.3 (SEM 0.9) nmol.l-1] compared to AB [21.9 (SEM 3.6) nmol.l-1], and increased PRE to END only in WA. Cortisol concentrations were similar between groups before and during exercise, despite higher rectal temperatures in WA compared to AB, at MID [37.21 (SEM 0.14) and 37.02 (SEM 0.08) degrees C, respectively] and END [37.36 (SEM 0.16) and 37.19 (SEM 0.10) degrees C, respectively]. Plasma norepinephrine responses were similar between groups. In conclusion, there were no differences in plasma cortisol concentrations, which may have been due to the low relative exercise intensities employed. The greater exercise response in WA for plasma testosterone should be confirmed on a larger population. It could have been the result of the lower plasma testosterone concentrations at rest in our group.

Plasma vasopressin and aldosterone responses to oral and intravenous saline rehydration

This investigation examined plasma arginine vasopressin (AVP) and aldosterone (Ald) responses to 1) oral and intravenous (IV) methods of rehydration (Rh) and 2) different IV Rh osmotic loads. We hypothesized that AVP and Ald responses would be similar between IV and oral Rh and that the greater osmolality and sodium concentration of a 0.9% IV saline treatment would stimulate a greater AVP response compared with a 0.45% IV saline treatment. On four occasions, eight men (age: 22.1 +/- 0.8 yr; height: 179.6 +/- 1.5 cm; weight: 73.6 +/- 2.5 kg; maximum O(2) consumption: 57.9 +/- 1.6 ml. kg(-1). min(-1), body fat: 7.7 +/- 0.9%) performed a dehydration (Dh) protocol (33 degrees C) to establish a 4-5% reduction in body weight. After Dh, subjects underwent each of three randomly assigned Rh (back to -2% body wt) treatments (0.9 and 0.45% IV saline, 0.45% oral saline) and a no Rh treatment during the first 45 min of a 100-min rest period. Blood samples were obtained pre-Dh, immediately post-Dh, and at 15, 35, and 55 min post-Rh. Before Dh, plasma AVP and Ald were not different among treatments but were significantly elevated post-Dh. In general, at 15, 35, and 55 min post-Rh, AVP, Ald, osmolality, and plasma volume shifts did not differ between IV and oral fluid replacement. These results demonstrated that the manner in which plasma AVP and Ald responded to oral and IV Rh or to different sodium concentrations (0.9 vs. 0.45%) was not different given the degree of Dh (-4.5% body wt) and Rh and amount of time after Rh (55 min).

Intravenous versus oral rehydration during a brief period: stress hormone responses to subsequent exhaustive exercise in the heat

The purpose of this study was to determine if intravenous fluid rehydration, versus oral rehydration, during a brief period (20 min) differentially affects plasma ACTH, cortisol, and norepinephrine concentrations during subsequent exhaustive exercise in the heat. Following dehydration (DHY) to Eth 4% of body weight, 8 nonacclimated highly trained males (age = 23.5 +/- 1.2 years, VáO2peak = 61.4 +/- 0.8 ml á kg á min-1, % body fat = 13.5 +/- 0. 6%) cycled to exhaustion at 74% VáO2peak in 36.8 C on three different occasions. These included: (a) no fluid (NF), where no fluid was provided during the rehydration period; (b) DRINK, where oral rehydration (0.45% NaCl) was provided equal to 50% of the prior DHY; and (c) IV, where intravenous infusion (0.45% NaCl) was provided equal to 50% of the prior DHY. Exercise time to exhaustion was not different (p =.07) between the DRINK (34.86 +/- 4.01) and IV (29.48 +/- 3.50) trials, but both were significantly (p <.05) longer than the NF (18.95 +/- 2.73) trial. No differences (p >.05) were found for any of the hormone measures among trials. The endocrine responses at exhaustion were similar regardless of hydration state and mode of rehydration, but rehydration prolonged the exercise time to exhaustion.

National athletic trainers' association position statement: fluid replacement for athletes

OBJECTIVE

To present recommendations to optimize the fluid-replacement practices of athletes.

BACKGROUND

Dehydration can compromise athletic performance and increase the risk of exertional heat injury. Athletes do not voluntarily drink sufficient water to prevent dehydration during physical activity. Drinking behavior can be modified by education, increasing accessibility, and optimizing palatability. However, excessive overdrinking should be avoided because it can also compromise physical performance and health. We provide practical recommendations regarding fluid replacement for athletes.

RECOMMENDATIONS

Educate athletes regarding the risks of dehydration and overhydration on health and physical performance. Work with individual athletes to develop fluid-replacement practices that optimize hydration status before, during, and after competition.

Intravenous versus oral rehydration during a brief period: responses to subsequent exercise in the heat

PURPOSE

The purpose of this study was to assess whether a brief period (20 min) of intravenous (i.v.) fluid rehydration versus oral rehydration differentially affects cardiovascular, thermoregulatory, and performance factors during exhaustive exercise in the heat.

METHODS

Following dehydration (-4% of body weight), eight nonacclimated highly trained cyclists (age = 23.5 +/- 1.2 yr; VO2peak = 61.4 +/- 0.8 mL x kg x min(-1); body fat = 13.5 +/- 0.6%) rehydrated and then cycled at 70% VO2peak to exhaustion in 37 degrees C. Rehydration (randomized, cross-over design) included: 1) CONTROL (no fluid), 2) DRINK (oral rehydration, 0.45% NaCl) equal to 50% of prior dehydration, and 3) IV (intravenous rehydration, 0.45% NaCl), equal to 50% of prior dehydration. Thus, in the DRINK and IV treatments subjects began exercise (EX) at -2% of body weight.

RESULTS

Exercise time to exhaustion was not different (P = 0.07) between DRINK (34.9 +/- 4 min) and IV (29.5 +/- 3.5 min), but both were significantly (P < 0.05) longer than CONTROL (18.9 +/- 2.7 min). Plasma volume was better (P < 0.05) restored during IV than CONTROL and DRINK at pre-exercise and 5 min EX, but different (P < 0.05) from only CONTROL at 15 min EX. Plasma lactate during DRINK was lower (P < 0.05) than IV at 15 min EX and postexercise. Heart rate during CONTROL was greater (P < 0.05) than DRINK and IV from 0-8 min EX, and greater (P < 0.05) than DRINK from 10-14 min EX. Rectal temperature during DRINK was less (P < 0.05) than IV from 0-24 min EX. Mean weighted skin temperature during DRINK was less (P < 0.05) than IV from 4-12 min EX.

CONCLUSIONS

Thus, despite no statistically significant performance differences between DRINK and IV, it appears that certain physiological parameters were better maintained in the DRINK trial, and the trend toward performance differences may be important to elite athletes.

T cells contribute to disease severity during coxsackievirus B4 infection

By using a model of coxsackievirus B4-induced disease, the question of whether tissue damage is due to the virus or to immune-mediated mechanisms was addressed. Both viral replication and T-cell function were implicated in contributing to the severity of disease. Three stages (I to III) of disease, which correspond to periods of high viral titers, low viral titers, and no infectious virus, have been identified. Stage I disease is considered to be primarily the result of viral replication. Immunopathological mechanisms appear to contribute to the severity of stage II and III disease. To investigate the role of T cells in contributing to the severity of disease, viral infection in CD8 knockout (ko) mice and CD4 ko mice was analyzed. CD8 T-cell responses appear to be beneficial during early, viral disease but detrimental in later disease when viral titers are diminishing. CD4 ko mice, unlike the parental strain, survived infection. Viral replication was lower in the CD4 ko mice. Was survival due to decreased viral replication or to the lack of T-helper-cell function? To investigate further the role of T helper cells in contributing to tissue damage, viral infection in two additional ko strains (interleukin-4 [IL-4] ko and gamma interferon ko strains) was examined. A clear correlation between viral replication and the outcome of infection was not observed. The absence of IL-4, which may influence T-helper-cell subset development, was advantageous during early viral disease but deleterious in later disease. The results suggest that T-cell-mediated immunity is both beneficial and detrimental during coxsackievirus B4 infection.

Fluid-electrolyte balance during labor and exercise: concepts and misconceptions

Body water and electrolyte balance are essential to optimal physiological function and health. During exercise, work, or high temperatures, a significant level of dehydration can develop, and the ratio of extracellular to intracellular fluid can change, despite an ample supply of water. Physical and cognitive performance are impaired at 1-2% dehydration, and the body can collapse when water loss approaches 7%. Because fluid needs and intakes vary, formulating one general guideline for fluid replacement is difficult. Knowing the amount of water lost in sweat may enable predicting fluid needs via mathematical models for industrial, athletic, and military scenarios. Sodium imbalance might result from excessive Na+ loss or from gross overhydration. In most work or exercise lasting < 3-4 hr, the major concern is that fluid be available to prevent heat-related illnesses, which can be prevented if fluid and electrolyte losses are balanced with intake, using the recommendations presented.

Urinary indices during dehydration, exercise, and rehydration

This investigation evaluated the validity and sensitivity of urine color (Ucol), specific gravity (Usg), and osmolality (Uosm) as indices of hydration status, by comparing them to changes in body water. Nine highly trained males underwent a 42-hr protocol involving dehydration to 3.7% of body mass (Day 1, -2.64 kg), cycling to exhaustion (Day 2, -5.2% of body mass, -3.68 kg), and oral rehydration for 21 hr. The ranges of mean (across time) blood and urine values were Ucol, 1-7; Usg, 1.004-1.029; Uosm, 117-1,081 mOsm x kg-1; and plasma osmolality (Posm), 280-298 mOsm x kg-1. Urine color tracked changes in body water as effectively as (or better than) Uosm, Usg, urine volume, Posm, plasma sodium, and plasma total protein. We concluded that (a) Ucol, Uosm, and Usg are valid indices of hydration status, and (b) marked dehydration, exercise, and rehydration had little effect on the validity and sensitivity of these indices.

Effects of training, environment, and host factors on the sweating response to exercise

Because metabolic heat production is proportional to the amount of work performed, the differences in core body temperature (Tcore) of humans exercising at similar absolute exercise intensities are due to differences in their efficiency of heat dissipation. The purpose of this paper is to delineate the effects of training status, heat acclimation, environmental conditions and host factors on the sweating response to exercise. These factors are reviewed in light of their effects on the biophysical enhancement or suppression of sweating, and modifications of the relationship between local sweat rate and Tcore (degrees C). Athletes are advised to optimize those factors that enhance, and eliminate those factors that diminish, the onset and responsiveness of sweating.

Plasma testosterone and cortisol responses to training-intensity exercise in mild and hot environments

Seven endurance-trained and heat-nonacclimated men (Mean+/-SEM: 20+/-1 yr; VO2max = 67+/-2 ml x kg(-1) x min(-1)) ran in two environments (M: 23 degrees C, H: 38 degrees C; 7 days apart) at two absolute training-intensity velocities (S1: 240 m x min(-1); followed by S2: 270 m x min(-1); 10 min each) during the winter months. Blood samples were taken via cannula before (pre) S1 and after S1 and S2. Plasma testosterone (TEST) concentrations increased (p<0.05) above pre levels after S1 in M (19+/-3 versus 24+/-3 nmol x L(-1)) and H (18+/-2 versus 23+/-3 nmol x L(-1)), and after S2 in H (18+/-2 versus 24+/-1 nmol x L(-1)). Plasma cortisol (CORT) and the molar ratio of TEST/CORT were unchanged from pre levels after S1 and S2 during M and H. No differences were found in plasma TEST, CORT, or the molar ratio of TEST/CORT between M and H. These results indicated that circulating levels of TEST and CORT were not changed in endurance-trained, heat-nonacclimated athletes in response to short-duration running performed at the same absolute intensity in the heat, compared to mild environmental conditions. The lack of significant differences in the molar ratio of TEST/CORT, between the 23 degrees C and 38 degrees C trials, suggested that this short-duration exercise challenge performed in the heat was no more of an anabolic or catabolic stimulus for these athletes.

Cardiovascular responses in a whirlpool bath at 40 degrees C versus user-controlled water temperatures

OBJECTIVE

To compare cardiovascular responses in a whirlpool bath at 40 degrees C versus user-controlled water temperature (UCT).

MATERIAL AND METHODS

In an experimental study, six healthy men, 36 to 43 years of age, participated in two randomly assigned trials of whirlpool bath use for 25 minutes at 40 degrees C and UCT. Water temperature, esophageal temperature (Tes) heart rate (HR), systolic blood pressure (SBP), and perceived comfort were monitored before immersion and at 5-minute intervals during immersion.

RESULTS

Although the mean water temperature during the UCT trial was slightly below 40 degrees C (39.4 +/- 2.0 degrees C), it varied considerably among subjects (from 36.5 +/- 2.1 degrees C to 42.5 +/- 1.7 degrees C). Peak Tes9 HR, and SBP were not significantly different between the two trials, although the UCT trial had greater variability. No adverse effects were observed. Mild or moderate overheating was reported by four subjects in the 40 degrees C trial and two subjects in the UCT trial, and mild chest pain, light-headedness, dyspnea, and nausea were reported by one subject during the UCT trial. A trend toward higher comfort ratings was noted in the UCT than in the 40 degrees C trial, especially during the final 10 minutes of immersion.

CONCLUSION

These data show that cardiovascular responses to whirlpool bathing for 25 minutes at 40 degrees C are mild. In comparison with the 40 degrees C trial, peak Tes9, HR, and SBP under UCT conditions were not, on the average, significantly higher, although more variability existed among the subjects.

Endocrine responses during exercise-heat stress: effects of prior isotonic and hypotonic intravenous rehydration

Exercise following exercise-induced dehydration (EID) has been shown to elevate concentrations of plasma norepinephrine (NE) and hypothalamic-pituitary-adrenal axis hormones. However, it is not known how intravenous (i.v.) rehydration (Rh) with isotonic (ISO) or hypotonic (HYPO) saline affects these hormone concentrations. It was hypothesized that HYPO, versus ISO, would lead to lower plasma NE and cortisol concentrations ([CORT]) during subsequent exercise following EID due to a decrease in plasma sodium concentration [Na+]. Eight non-heat acclimated men completed three experimental treatments (counterbalanced design) immediately following EID (33 degrees C) to -4% body mass loss. The Rh treatments were i.v. 0.9% NaCl (ISO, 25 ml x kg[-1]), i.v. 0.45% NaCl (HYPO, 25 ml x kg[-1]), and no fluid (NF). After Rh and rest (2 h total), the subjects walked at 53-54 percent of maximal O2 uptake for 45 min at 36 degrees C. After Rh, the following observations were made before/during exercise: percentage change in plasma volume (PV) was lower in NF compared to ISO and HYPO but similar between ISO and HYPO; delta[Na+] was similar between ISO and NF and higher in ISO compared to HYPO; delta plasma NE was higher in NF compared to ISO and HYPO, but similar between ISO and HYPO; delta plasma [CORT] was higher in NF compared to ISO and HYPO and higher in ISO compared to HYPO; rectal temperature was higher in NF compared to ISO and HYPO. These data would suggest that sympathetic nervous activity and [CORT] during exercise, subsequent to EID and Rh, was affected by lower PV (probably through cardiopulmonary baroreflexes) as well as core temperature. Furthermore, [CORT] was affected by delta[Na+] after Rh through an unknown mechanism.

Chronobiological effects on exercise performance and selected physiological responses

Previous studies investigating the impact of circadian rhythms on physiological variables during exercise have yielded conflicting results. The purpose of the present investigation was to examine maximal aerobic exercise performance, as well as the physiological and psychophysiological responses to exercise, at four different intervals (0800 hours, 1200 hours, 1600 hours, and 2000 hours) within the segment of the 24-h day in which strenuous physical activity is typically performed. Ten physically fit, but untrained, male university students served as subjects. The results revealed that exercise performance was unaffected by chronobiological effects. Similarly, oxygen uptake, minute ventilation and heart rate showed no time of day influences under pre-, submaximal, and maximal exercise conditions. Ratings of perceived exertion were unaffected by time of day effects during submaximal and maximal exercise. In contrast, rectal temperature exhibited a significant chronobiological rhythm under all three conditions. Under pre- and submaximal exercise conditions, significant time of day effects were noted for respiratory exchange ratio, while a significant rhythmicity of blood pressure was evident during maximal exercise. However, none of these physiological variables exhibited significant differential responses (percent change from pre-exercise values) to the exercise stimulus at any of the four time points selected for study. Conversely, resting plasma lactate levels and lactate responses to maximal exercise were found to be significantly sensitive to chronobiological influences. Absolute post-exercise plasma norepinephrine values, and norepinephrine responses to exercise (percent change from pre-exercise values), also fluctuated significantly among the time points studied. In summary, these data suggest that aerobic exercise performance does not vary during the time frame within which exercise is normally conducted, despite the fact that some important physiological responses to exercise do fluctuate within that time period.

Bioimpedance spectroscopy technique: intra-, extracellular, and total body water

The purpose of this study was to test the validity of a multiple frequency bioimpedance spectroscopy (BIS) technique that estimates extracellular fluid volume (ECV), intracellular fluid volume (ICV), and total body water (TBW). Thirteen healthy males (mean +/- SD: age, 23 +/- 3 yr; body mass, 80.6 +/- 14.7 kg) had their TBW and ECV measured by ingesting dilution tracers (7.27 g deuterium oxide, 1.70 g sodium bromide; blood samples at 0 and 4 h). ICV was calculated as TBW minus ECV. Impedance was measured (50-500 kHz) at rest, on a nonconducting surface, with a BIS analyzer. Electrode placement, posture, exercise, food/fluid intake, and ambient temperature were controlled. Dilution measures (TBW, 51.00 +/- 9.30; ECV, 19.88 +/- 3.14; ICV, 31.12 +/- 6.80 L) and BIS volumes (TBW, 50.03 +/- 7.67; ECV, 20.95 +/- 3.33; ICV, 29.04 +/- 4.51 L) were significantly different for ECV (P < 0.01) and ICV (P < 0.05); some individual differences were large. The correlation coefficients of dilution versus BIS volumes (r = 0.93 to 0.96) were significant at P < 0.0001; SEEs were: TBW, 2.23 L; ECV, 1.26 L; and ICV, 1.71 L. We concluded that BIS is valid for between-subject comparisons of body fluid compartments, is appropriate in clinical settings where change in ECV/ICV ratio is important, and should be used by comparing the required level of accuracy to the inherent technique error/variance.

Differential recruitment of B and T cells in coxsackievirus B4-induced pancreatitis is influenced by a capsid protein

Two genetically similar variants of coxsackievirus B4, CB4-P and CB4-V, cause distinct disease syndromes in mice. A multidisciplinary approach was used to examine the events occurring in situ. The CB4-P variant induced acute pancreatitis, followed by repair of the exocrine tissues, while the CB4-V variant induced chronic pancreatitis, characterized by extensive destruction of the exocrine tissues. Since CB4-V replicated more efficiently than CB4-P in vivo, the more extensive tissue injury associated with CB4-V infection could be explained as the result of a higher level of viral replication. However, the fact that CB4-V replicated more efficiently in a mouse strain that survives infection than in a strain that succumbs to infection suggests that immune-mediated mechanisms as well as viral cytolysis may contribute to pancreatic tissue injury. To address the role of the immune system in virus-induced pancreatitis, the cell types within the inflammatory infiltrate were analyzed by flow cytometry. B cells (34 to 75%) were the most abundant, followed by T cells (10 to 30%), natural killer cells (4 to 8%), and macrophages (0 to 6%). Recruitment (and perhaps proliferation) of B and T cells to the pancreatic tissues was influenced by viral strain. Differential recruitment of T and B cells may reflect altered antigenic sites between CB4-P and CB4-V. The viral sequence that affected T- and B-cell recruitment was identified as a threonine residue at position 129 of the VP1 capsid protein.

Thermal and circulatory responses during exercise: effects of hypohydration, dehydration, and water intake

This investigation examined the distinct and interactive effects of initial hydration state, exercise-induced dehydration, and water rehydration in a hot environment. On four occasions, 10 men performed a 90-min heat stress test (treadmill walking at 5.6 km/h, 5% grade, 33 degrees C, 56% relative humidity). These heat stress tests differed in pretest hydration [2 euhydrated (EU) and 2 hypohydrated (HY) trials] and water intake during exercise [2 water ad libitum (W) and 2 no water (NW) trials]. HY+NW indicated greater physiological strain than all other trials (P < 0.05-0.001) in heart rate, plasma osmolality (Posm), sweat sensitivity (g/degrees C.min), and rectal temperature. Unexpectedly, final HY+W and EU+W responses for rectal temperature, heart rate, and Posm were similar, despite the initial 3.9 +/- 0.2% hypohydration in HY+W. We concluded that differences in pretest Posm (295 +/- 7 and 287 +/- 5 mosmol/kg for HY+W and EU+W, respectively) resulted in greater water consumption (1.65 and 0.31 liter for HY+W and EU+W, respectively), no voluntary dehydration (0.9% body mass increase), and attenuated thermal and circulatory strain during HY+W.

Intravenous vs. oral rehydration: effects on subsequent exercise-heat stress

This study compared the influence of intravenous vs. oral rehydration after exercise-induced dehydration during a subsequent 90-min exercise bout. It was hypothesized that cardiovascular, thermoregulatory, and hormonal variables would be the same between intravenous and oral rehydration because of similar restoration of plasma volume (PV) and osmolality (Osmo). Eight non-heat-acclimated men received three experimental treatments (counterbalanced design) immediately after exercise-induced dehydration (33 degrees C) to -4% body weight loss. Treatments were intravenous 0.45% NaCl (iv; 25 ml/kg), no fluid (NF), and oral saline (Oral; 25 ml/kg). After rehydration and rest (2 h total), subjects walked at 50% maximal O2 consumption for up to 90 min at 36 degrees C. The following observations were made: 1) heart rate was higher (P < 0.05) in Oral vs. iv at minutes 45, 60, and 75 of exercise; 2) rectal temperature, sweat rate, percent change in PV, and change in plasma Osmo were similar between iv and Oral; 3) change in plasma norepinephrine decreased less (P < 0.05) in Oral compared with iv at minute 45; 4) changes in plasma adrenocorticotropic hormone and cortisol were similar between iv and Oral after exercise was initiated; and 5) exercise time was similar between iv (77.4 +/- 5.4 min) and Oral (84.2 +/- 2.3 min). These data suggest that after exercise-induced dehydration, iv and Oral were equally effective as rehydration treatments. Thermoregulation, change in adrenocorticotropic hormone, and change in cortisol were not different between iv and Oral after exercise began; this is likely due to similar percent change in PV and change in Osmo.

Physiological and psychological effects associated with high carbon dioxide levels in healthy men

BACKGROUND

Perception of CO2 in ambient air may be of fundamental importance to the health, safety, and job performance of persons occupationally exposed to increased levels of CO2. Few studies have examined the perceptual responses to inhaled CO2 at levels between 6-10%.

HYPOTHESIS

We hypothesized that healthy, highly-active men would be able to determine the difference between 6% and 8% CO2 concentrations.

METHODS

Thirty-two male students (21 +/- 1 yr) served as subjects. Experimental trials (counterbalanced design) included breathing air (control, 21% O2, 79% N2), 6% CO2 (21% O2, 73% N2), and 8% CO2 (21% O2, 71% N2) conditions. The Body Sensations Questionnaire (BSQ) was completed twice during each trial.

RESULTS

End tidal CO2 (FETCO2) and BSQ values increased (p < 0.05) as a function of the percentage of inhaled CO2. Respiratory rates during the 8% trial were greater (p < 0.05) than control and 6% CO2 trial measures. BSQ scores were significantly correlated with FETCO2 and respiratory rate measures during the 6% and 8% CO2 conditions.

CONCLUSIONS

We conclude that these subjects recognized their exposure to both the 6% and 8% CO2 concentrations, and their responses were more profound during the 8% CO2 condition.

Effects of oral and intravenous rehydration on ratings of perceived exertion and thirst

The purpose of this investigation was to compare the effects of oral and intravenous saline rehydration on differentiated ratings of perceived exertion (RPE) and thirst. Eight men underwent three randomly assigned rehydration treatments following a 2- to 4-h exercise-induced dehydration bout to reduce body weight by 4%. Treatments included 0.45% saline infusion (i.v.), 0.45% saline oral ingestion (ORAL), and no fluid (NF). Following rehydration and rest (2 h total), subjects walked at 50% VO2max for 90 min at 36 degrees C (EX). Central RPE during ORAL was lower (P < 0.05) than i.v. and NF throughout EX. Local RPE during NF was higher (P < 0.05) than i.v. and ORAL at minutes 20 and 40 of EX and overall RPE during NF was higher (P < 0.05) than ORAL at minutes 20 and 40 of EX. Significant correlations were found between overall RPE and mean skin temperature for i.v. (r = 0.72) and NF (r = 0.75), and between overall RPE and thirst ratings for i.v. (r = 0.70). Thirst ratings were not different among trials at postdehydration. Following rehydration, thirst was higher (P < 0.05) during NF than i.v. and ORAL and lower (P < 0.05) during ORAL than i.v. at all subsequent time points. Results suggest that oral rehydration is likely to elicit lower RPE and thirst ratings compared with intravenous rehydration.

American College of Sports Medicine position stand. Heat and cold illnesses during distance running

Many recreational and elite runners participate in distance races each year. When these events are conducted in hot or cold conditions, the risk of environmental illness increases. However, exertional hyperthermia, hypothermia, dehydration, and other related problems may be minimized with pre-event education and preparation. This position stand provides recommendations for the medical director and other race officials in the following areas: scheduling; organizing personnel, facilities, supplies, equipment, and communication; providing competitor education; measuring environmental stress; providing fluids; and avoiding potential legal liabilities. This document also describes the predisposing conditions, recognition, and treatment of the four most common environmental illnesses: heat exhaustion, heatstroke, hypothermia, and frostbite. The objectives of this position stand are: 1) To educate distance running event officials and participants about the most common forms of environmental illness including predisposing conditions, warning signs, susceptibility, and incidence reduction. 2) To advise race officials of their legal responsibilities and potential liability with regard to event safety and injury prevention. 3) To recommend that race officials consult local weather archives and plan events at times likely to be of low environmental stress to minimize detrimental effects on participants. 4) To encourage race officials to warn participants about environmental stress on race day and its implications for heat and cold illness. 5) To inform race officials of preventive actions that may reduce debilitation and environmental illness. 6) To describe the personnel, equipment, and supplies necessary to reduce and treat cases of collapse and environmental illness.

Whole-body cooling of hyperthermic runners: comparison of two field therapies

Severe exercise-induced hyperthermia requires rapid cooling. Of the many cooling modalities available, there is disagreement over which is the most effective. The purpose of this field study was to compare two cooling therapies for hyperthermic distance runners who had completed an 11.5-km summer foot race. Twenty-one distance runners (mean [+/- SE] initial rectal temperature 41.2 +/- 0.2 degrees C) were treated either by ice water immersion (1 to 3 degrees C, n = 14) or by air exposure while wrapped in wet towels (24.4 degrees C ambient, n = 7). Ice water immersion versus air exposure resulted in significantly different (P < .005) pretherapy to posttherapy changes in rectal temperature (-3.0 +/- 0.3 v -1.4 +/- 0.3 degrees C) and mean cooling rate (0.20 +/- 0.02 v 0.11 +/- 0.02 degrees C/min). Ice water immersion cooled approximately twice as fast as air exposure. These data refute the theory that ice water immersion is an inefficient cooling modality.

Plasma volume responses to consecutive anaerobic exercise tests

This study examined the change in plasma volume (% delta PV) in response to consecutive Wingate tests (30 sec Anaerobic Power test). Twelve active men (21 +/- 1.6 yr, 81.3 +/- 6.6 kg) performed two Wingate tests (W1 and W2, separated by 10 min) on three occasions (T1-T3, tests were two weeks apart). Exercise resistance was maintained at 75 g.kg-1 body weight during testing. Blood samples were taken immediately before (Pre) and after (IP) W1 and W2. There were no significant differences in hematocrit, hemoglobin, mean power (MP) or peak power (PP) between T1-T3. There was a marked hemoconcentration in response to W1 (IP W1, -17.4 +/- 2.6% delta PV), with a further, but not significantly greater, hemoconcentration following W2 (IP W2, -8.2 +/- 1.1% delta PV). The % delta PV, between PRE W1 and IP W2 was-20.1 +/- 3.1%. These results suggest that an existing hemoconcentration (W1) may affect the magnitude of the % delta PV response to subsequent supramaximal exercise (W2).

American College of Sports Medicine position stand. Exercise and fluid replacement

It is the position of the American College of Sports Medicine that adequate fluid replacement helps maintain hydration and, therefore, promotes the health, safety, and optimal physical performance of individuals participating in regular physical activity. This position statement is based on a comprehensive review and interpretation of scientific literature concerning the influence of fluid replacement on exercise performance and the risk of thermal injury associated with dehydration and hyperthermia. Based on available evidence, the American College of Sports Medicine makes the following general recommendations on the amount and composition of fluid that should be ingested in preparation for, during, and after exercise or athletic competition: 1) It is recommended that individuals consume a nutritionally balanced diet and drink adequate fluids during the 24-hr period before an event, especially during the period that includes the meal prior to exercise, to promote proper hydration before exercise or competition. 2) It is recommended that individuals drink about 500 ml (about 17 ounces) of fluid about 2 h before exercise to promote adequate hydration and allow time for excretion of excess ingested water. 3) During exercise, athletes should start drinking early and at regular intervals in an attempt to consume fluids at a rate sufficient to replace all the water lost through sweating (i.e., body weight loss), or consume the maximal amount that can be tolerated. 4) It is recommended that ingested fluids be cooler than ambient temperature [between 15 degrees and 22 degrees C (59 degrees and 72 degrees F])] and flavored to enhance palatability and promote fluid replacement. Fluids should be readily available and served in containers that allow adequate volumes to be ingested with ease and with minimal interruption of exercise. 5) Addition of proper amounts of carbohydrates and/or electrolytes to a fluid replacement solution is recommended for exercise events of duration greater than 1 h since it does not significantly impair water delivery to the body and may enhance performance. During exercise lasting less than 1 h, there is little evidence of physiological or physical performance differences between consuming a carbohydrate-electrolyte drink and plain water. 6) During intense exercise lasting longer than 1 h, it is recommended that carbohydrates be ingested at a rate of 30-60 g.h(-1) to maintain oxidation of carbohydrates and delay fatigue. This rate of carbohydrate intake can be achieved without compromising fluid delivery by drinking 600-1200 ml.h(-1) of solutions containing 4%-8% carbohydrates (g.100 ml(-1)). The carbohydrates can be sugars (glucose or sucrose) or starch (e.g., maltodextrin). 7) Inclusion of sodium (0.5-0.7 g.1(-1) of water) in the rehydration solution ingested during exercise lasting longer than 1 h is recommended since it may be advantageous in enhancing palatability, promoting fluid retention, and possibly preventing hyponatremia in certain individuals who drink excessive quantities of fluid. There is little physiological basis for the presence of sodium in n oral rehydration solution for enhancing intestinal water absorption as long as sodium is sufficiently available from the previous meal.

Plasma norepinephrine responses to cycle exercise in boys and men

Previous reports have suggested that plasma norepinephrine levels during exercise, an indicator of sympathetic neurologic activity, may be less in children than in adults. This study investigated plasma norepinephrine values at rest, during two submaximal cycle exercise intensities, and at maximal exercise in 11 boys aged 10 to 12 years and 11 men aged 24 to 35 years. Blood specimens were drawn at average submaximal exercise intensities of 58.7% and 73.0% for the boys and 55.3% and 73.3% VO2max for the men. Weight-relative maximal aerobic power was similar in the two groups. No statistically-significant differences were observed in plasma norepinephrine values at rest or during submaximal and maximal exercise between the boys and men. Maximal levels were 1196 (326 SD) and 1385 (612 SD) pg.ml-1 for the boys and men, respectively (p > 0.05). These findings suggest that sympathetic influences during maximal and submaximal exercise are independent of biological maturation.

Fluid-electrolyte balance associated with tennis match play in a hot environment

Twenty (12 male and 8 female) tennis players from two Division I university tennis teams performed three days of round-robin tournament play (i.e., two singles tennis matches followed by one doubles match per day) in a hot environment (32.2 +/- 1.5 degrees C and 53.9 +/- 2.4% rh at 1200 hr), so that fluid-electrolyte balance could be evaluated. During singles play, body weight percentage changes were minimal and were similar for males and females (males -1.3 +/- 0.8%, females -0.7 +/- 0.8%). Estimated daily losses (mmol.day-1) of sweat sodium (Na+) and potassium (K+) (males, Na+ 158.7, K+ 31.3; females, Na+ 86.5, K+ 18.9) were met by the players' daily dietary intakes (mmol.day-1) of these electrolytes (males, Na+ 279.1 +/- 109.4, K+ 173.5 +/- 57.7; females, Na+ 178.9 +/- 68.9, K+ 116.1 +/- 37.5). Daily plasma volume and electrolyte (Na+, K+) levels were generally conserved, although, plasma [Na+] was lower (p < .05) on the morning of Day 4. This study indicated that these athletes generally maintained overall fluid-electrolyte balance, in response to playing multiple tennis matches on 3 successive days in a hot environment, without the occurrence of heat illness.

The effects of different treadmill running programs on the muscle morphology of adult rats

The biochemical adaptations of different muscle fiber types to endurance training of various intensities and durations have previously been investigated. The objective of this study was to determine the effects of two different endurance training programs on muscle fiber morphology. Twenty-four male Sprague-Dawley rats were randomly assigned to three groups: high intensity/low duration endurance trained (HILD), low intensity/high duration endurance trained (LIHD), or untrained (controls). Following the twelve week training period, muscle fibers of the gastrocnemius muscle of the rats were histochemically classified as type I, type IIa, or type IIb following myosin ATPase staining with pre-incubation at pH 4.6. Muscle fiber type distribution and cross-sectional areas were then determined. Neither HILD nor LIHD rats demonstrated significant differences in fiber type distribution compared to controls. When all fiber types were pooled together and analyzed, there were no differences between the three groups with respect to fiber size. However, when the three fiber types were analyzed individually, HILD animals demonstrated a significant reduction in the size of type IIa fibers while LIHD rats experienced a significant diminution in the size of type I and type IIb fibers. Thus, the morphological adaptations of the muscle fibers in the HILD and LIHD groups were fiber type specific.

Local cooling in wheelchair athletes during exercise-heat stress

Wheelchair athletes with spinal cord injuries (WA) face challenges to thermal homeostasis, including reduced cutaneous vasoaction and sweat production. The purpose of this study was to evaluate the efficacy of local cooling to reduce heat strain in WA. Six elite, endurance-trained male WA (33 +/- 3 yr, 64 +/- 4 kg) performed three strenuous exercise tests in a hot-humid environment (32.9 +/- 0.1 degrees C, 75 +/- 3% RH) by pushing a racing chair on a stationary roller (30 min, 16.5 km.h-1, 704-766 W metabolic heat) while wearing shorts and socks. The three treatments involved an ice-packet vest (V) (0.14 m2 of skin surface), a refrigerated headpiece (H) (0.16 m2), or no cooling (C) (control). The vest and headpiece offered potential cooling of 388 W and 266 W. Mean body heat storage for trials V (117 +/- 26 W), H (117 +/- 22 W), and C (164 +/- 40 W) were statistically similar, partly because V (117 +/- 47 W) and H (75 +/- 59 W) cooled inefficiently (30 and 28%, respectively). Repeated measure ANOVA indicated no significant between-treatment differences (P > 0.05) for any variable in trials V, H, and C. We concluded that local cooling during V and H was ineffective because heat storage decreased, but was not prevented.

Fluid and electrolyte losses during tennis in the heat

A tennis player's metabolism during play in a hot environment generates an abundance of heat, which is primarily eliminated from the body by evaporation of sweat. An individual's on-court rate of fluid loss will depend on the environmental conditions, intensity of play, acclimatization, aerobic fitness, hydration status, age, and gender. Unless fluid intake closely matches sweat loss, a progressive and significant body water deficit may develop that will proportionately impair cardiovascular and thermoregulatory functions. As a result, a player can experience an increase in core temperature, premature fatigue, performance decrements, and an increased potential for heat illness. Although sweat is hypotonic compared to plasma, extended tennis play, in a hot environment, can lead to sizable Na+ and Cl- losses. Also, ad libitum drinking often leads to involuntary dehydration in these conditions. Therefore, for tennis play and training in the heat, it is important to follow a hydration plan that will minimize on-court water deficits, by optimizing fluid availability, consumption, and absorption. For tennis matches greater than 1 hour in duration, a CHO-electrolyte drink (as described earlier) is the recommended on-court beverage.