Updated fluid recommendation: position statement from the International Marathon Medical Directors Association (IMMDA)

Limited Effect of Dehydrating via Active vs. Passive Heat Stress on Plasma Volume or Osmolality, Relative to the Effect of These Stressors per Se

The physiological, perceptual, and functional effects of dehydration may depend on how it is incurred (e.g., intense exercise releases endogenous water via glycogenolysis) but this basic notion has rarely been examined. We investigated the effects of active (exercise) heat- vs. passive heat-induced dehydration, and the kinetics of ad libitum rehydration following each method. Twelve fit participants (five females and seven males) completed four trials in randomised order: DEHydration to -3% change in body mass (∆BM) under passive or active heat stress, and EUHydration to prevent ∆BM under passive or active heat stress. In all trials, participants then sat in a temperate-controlled environment, ate a standard snack and had free access to water and sports drink during their two-hour recovery. During mild dehydration (≤2% ∆BM), active and passive heating caused comparable increases in plasma osmolality (P_osm: ~4 mOsmol/kg, interaction: p = 0.138) and reductions in plasma volume (PV: ~10%, interaction: p = 0.718), but heat stress per se was the main driver of hypovolaemia. Thirst in DEHydration was comparably stimulated by active than passive heat stress (p < 0.161) and shared the same relation to P_osm (r ≥ 0.744) and ∆BM (r ≥ 0.882). Following heat exposures, at 3% gross ∆BM, PV reduction was approximately twice as large from passive versus active heating (p = 0.003), whereas P_osm perturbations were approximately twice as large from EUHydration versus DEHydration (p < 0.001). Rehydrating ad libitum resulted in a similar net fluid balance between passive versus active heat stress and restored PV despite the incomplete replacement of ∆BM. In conclusion, dehydrating by 2% ∆BM via passive heat stress generally did not cause larger changes to PV or P_osm than via active heat stress. The heat stressors themselves caused a greater reduction in PV than dehydration did, whereas ingesting water to maintain euhydration produced large reductions in P_osm in recovery and therefore appears to be of more physiological significance.

Atopic Dermatitis and Water: Is There an Optimum Water Intake Level for Improving Atopic Skin?

Water is a vital nutrient with innumerable functions for every living cell. The functions of human skin include protection against dehydration of the body. Atopic dermatitis (AD) is a chronic pruritic inflammatory skin disease that presents with dry skin, erythematous and eczematous lesions, and lichenification. This paper discusses the question of whether extra water intake in children with AD affects skin hydration and the skin barrier function. Among the methods used to treat dry skin, topical leave-on products are the first-line treatment, intended to improve hydration and the skin barrier function. The effectiveness of adequate water intake as a measure to treat dry skin is still under debate. Normal skin hydration increases with dietary water intake, particularly in those with prior lower water consumption. Skin dryness in AD is instrumental to the itch and inflammation cycle, contributing to barrier impairment and aggravating disease severity and flares. Certain emollients provide significant hydration to AD skin, with relief of dryness and reduction in barrier impairment, disease severity, and flares. Further investigations are needed to evaluate the optimum water intake levels in children with AD, as important questions remain unanswered, namely, does oral hydration provide relief of skin dryness and reduce barrier impairment, disease severity, and flares; is there any additional benefit from using mineral or thermal spring water; or is there a need to specifically study the fluid/water intake in children with AD and food allergy (FA) restrictions?

The Caffeine Content of Energy Drinks in accordance with the Information on the Package Label

Six different brands of energy drinks (EDs) were analyzed to determine the concentration of caffeine in accordance with the information on the package label. Approximately 28.1 milligrams per 100 milliliters (mg/100 ml) of caffeine was present in the Mo energy drink brand, which was nearly 1.5 times the caffeine concentration listed on the product label. The energy drink with the highest caffeine content was Dragon, which contained 30.1 mg/100 ml, or a total of 150.5 mg per 500 ml bottle. Manufacturers of energy drinks (EDs) should accurately list the amount of caffeine and other ingredients on the product label so that consumers know how much of each ingredient they are taking. Taking too much caffeine can be bad for your health.

Hydration Strategies for Physical Activity and Endurance Events at High (>2500 m) Altitude: A Practical Management Article

A growing number of adventurous athletes are seeking new challenges through endurance events or physical activities held at high altitude (>2500 m). This coincides with a significant increase in the numbers of trekkers who ascend into the world's mountains. Altitude itself influences and complicates the athlete's effective and safe hydration. This article considers the physiology of adaptation to altitude and the effects on hydration at altitude compared with sea level, reviews the "ad libitum versus programmed hydration" controversy in conventional endurance event hydration, examines the evidence for extrapolation of sea level hydration strategies to the high-altitude environment, and synthesizes these disparate factors into a set of practical recommendations for hydration management during high-altitude physical activity. The guidelines will be relevant to participants of physical activity at altitude and health care staff who may care for them in the preparation or performance phases of their adventure.

The Influence of Environmental Conditions on Pacing in Age Group Marathoners Competing in the “New York City Marathon”

Background: The two aspects of the influence of environmental conditions on marathon running performance and pacing during a marathon have been separately and widely investigated. The influence of environmental conditions on the pacing of age group marathoners has, however, not been considered yet.

Objective: The aim of the present study was to investigate the association between environmental conditions (i.e., temperature, barometric pressure, humidity, precipitation, sunshine, and cloud cover), gender and pacing of age group marathoners in the “New York City Marathon”.

Methodology: Between 1999 and 2019, a total of 830,255 finishes (526,500 males and 303,755 females) were recorded. Time-adjusted averages of weather conditions for temperature, barometric pressure, humidity, and sunshine duration during the race were correlated with running speed in 5 km-intervals for age group runners in 10 years-intervals.

Results: The running speed decreased with increasing temperatures in athletes of age groups 20–59 with a pronounced negative effect for men aged 30–64 years and women aged 40–64 years. Higher levels of humidity were associated with faster running speeds for both sexes. Sunshine duration and barometric pressure showed no association with running speed.

Conclusion: In summary, temperature and humidity affect pacing in age group marathoners differently. Specifically, increasing temperature slowed down runners of both sexes aged between 20 and 59 years, whereas increasing humidity slowed down runners of &lt;20 and &gt;80 years old.

Exercise-Induced Hyponatremia: An Assessment of the International Hydration Recommendations Followed During the Gran Trail De Peñalara and Vitoria-Gasteiz Ironman Competitions

Introduction

Hyponatremia often occurs during the practice of endurance sports. We evaluated the impact on hyponatremia of the hydration recommendations of the Third International Exercise-Associated Hyponatremia Consensus Development Conference 2015 (3IE-AHCD) during the 2017 Gran Trail de Peñalara marathon (GTP) and the Vitoria Gasteiz Ironman triathlon (VGI).

Methods

Prospective study of GTP and VGI athletes participating in four information sessions in the months prior to the events, to explain that hydration should only be according to their level of thirst, per the recommendations of the 3IE-AHCD. Consenting event finishers were included in final analysis. Pre- and post-race anthropometric and biochemical parameters were compared.

Results

Thirty-six GTP (33 male) and 94 VGI (88 male) finishers were evaluated. GTP race median fluid intake was 800 ml/h, with 900 ml/h in the VGI race. 83.3% GTPfin and 77.6% VGIfin remained eunatremic (blood sodium 135–145 mmol/L). Only 1/36 GTP and 1/94 VGI participant finished in hyponatremia, both with a sodium level of 134 mmol/L. Fourteen percent of GTP, and 21.2% of VGI participants finished in hypernatremia, with no increase in race completion times. No participating athlete required medical attention, except for musculoskeletal complaints. Pro-BNP and Copeptin levels rose significantly. Changes in copeptin levels did not correlate with changes in plasma osmolality, nor total body water content in impedance analysis.

Conclusions

Recommending that athletes' fluid intake in endurance events be a function of their thirst almost entirely prevented development of hyponatremia, without induction of clinically significant hypernatremia, or a negative repercussion on race completion times.

Provision of instructions to drink ad libitum or according to thirst sensation: impact during 120 km of cycling in the heat in men

The terms drinking to thirst and ad libitum drinking are used interchangeably, but should they? We investigated the differences in how athletes consumed fluids during exercise when instructed to drink according to thirst or ad libitum. Using a randomized, crossover, and counterbalanced design, 10 males (27 ± 4 y) cycled 120 km (48 ± 4% of peak power, 33 °C, 40% relative humidity) on 2 occasions, while drinking water according to thirst or ad libitum. Participants covered the cycling trials in 222 ± 11 min (p = 0.29). Although the body mass loss at the end of exercise and total volume of water consumed were similar between trials, thirst perception before each sip and the volume consumed per sip were significantly higher with thirst than ad libitum drinking, whereas the total number of sips was significantly lower with thirst than ad libitum drinking. Perceived exertion, rectal temperature, and heart rate were all significantly higher with thirst than ad libitum drinking, but the difference was trivial. In conclusion, thirst and ad libitum drinking are associated with different drinking patterns, but equally maintain fluid balance during prolonged exercise. The terms drinking to thirst and ad libitum drinking can be used interchangeably to guide fluid intake during prolonged exercise. Novelty: Both strategies are associated with different patterns of fluid ingestion during prolonged exercise, but are equally effective in maintaining fluid balance. Perceived exertion, rectal temperature, and heart rate are regulated dissimilarly by thirst and ad libitum drinking, but the difference is trivial.

Changes in Hydration Factors Over the Course of Heat Acclimation in Endurance Athletes

The purpose of this study was to examine the effect of heat acclimation (HA) on thirst levels, sweat rate, and percentage of body mass loss (%BML), and changes in fluid intake factors throughout HA induction. Twenty-eight male endurance athletes (mean ± SD; age, 35 ± 12 years; body mass, 73.0 ± 8.9 kg; maximal oxygen consumption, 57.4 ± 6.8 ml·kg-1·min-1) completed 60 min of exercise in a euhydrated state at 58.9 ± 2.3% velocity of maximal oxygen consumption in the heat (ambient temperature, 35.0 ± 1.3 °C; relative humidity, 48.0 ± 1.3%) prior to and following HA where thirst levels, sweat rate, and %BML were measured. Then, participants performed 5 days of HA while held at hyperthermia (38.50-39.75 °C) for 60 min with fluid provided ad libitum. Sweat volume, %BML, thirst levels, and fluid intake were measured for each session. Thirst levels were significantly lower following HA (pre, 4 ± 1; post, 3 ± 1, p < .001). Sweat rate (pre, 1.76 ± 0.42 L/hr; post, 2.00 ± 0.60 L/hr, p = .039) and %BML (pre, 2.66 ± 0.53%; post, 2.98 ± 0.83%, p = .049) were significantly greater following HA. During HA, thirst levels decreased (Day 1, 4 ± 1; Day 2, 3 ± 2; Day 3, 3 ± 2; Day 4, 3 ± 1; Day 5, 3 ± 1; p < .001). However, sweat volume (Day 1, 2.34 ± 0.67 L; Day 2, 2.49 ± 0.58 L; Day 3, 2.67 ± 0.63 L; Day 4, 2.74 ± 0.61 L; Day 5, 2.74 ± 0.91 L; p = .010) and fluid intake (Day 1, 1.20 ± 0.45 L; Day 2, 1.52 ± 0.58 L; Day 3, 1.69 ± 0.63 L; Day 4, 1.65 ± 0.58 L; Day 5, 1.74 ± 0.51 L; p < .001) increased. In conclusion, thirst levels were lower following HA even though sweat rate and %BML were higher. Thirst levels decreased while sweat volume and fluid intake increased during HA induction. Thus, HA should be one of the factors to consider when planning hydration strategies.

Exercise under heat stress: thermoregulation, hydration, performance implications, and mitigation strategies

A rise in body core temperature and loss of body water via sweating are natural consequences of prolonged exercise in the heat. This review provides a comprehensive and integrative overview of how the human body responds to exercise under heat stress and the countermeasures that can be adopted to enhance aerobic performance under such environmental conditions. The fundamental concepts and physiological processes associated with thermoregulation and fluid balance are initially described, followed by a summary of methods to determine thermal strain and hydration status. An outline is provided on how exercise-heat stress disrupts these homeostatic processes, leading to hyperthermia, hypohydration, sodium disturbances, and in some cases exertional heat illness. The impact of heat stress on human performance is also examined, including the underlying physiological mechanisms that mediate the impairment of exercise performance. Similarly, the influence of hydration status on performance in the heat and how systemic and peripheral hemodynamic adjustments contribute to fatigue development is elucidated. This review also discusses strategies to mitigate the effects of hyperthermia and hypohydration on exercise performance in the heat by examining the benefits of heat acclimation, cooling strategies, and hyperhydration. Finally, contemporary controversies are summarized and future research directions are provided.

Rehydration during Endurance Exercise: Challenges, Research, Options, Methods

During endurance exercise, two problems arise from disturbed fluid-electrolyte balance: dehydration and overhydration. The former involves water and sodium losses in sweat and urine that are incompletely replaced, whereas the latter involves excessive consumption and retention of dilute fluids. When experienced at low levels, both dehydration and overhydration have minor or no performance effects and symptoms of illness, but when experienced at moderate-to-severe levels they degrade exercise performance and/or may lead to hydration-related illnesses including hyponatremia (low serum sodium concentration). Therefore, the present review article presents (a) relevant research observations and consensus statements of professional organizations, (b) 5 rehydration methods in which pre-race planning ranges from no advanced action to determination of sweat rate during a field simulation, and (c) 9 rehydration recommendations that are relevant to endurance activities. With this information, each athlete can select the rehydration method that best allows her/him to achieve a hydration middle ground between dehydration and overhydration, to optimize physical performance, and reduce the risk of illness.

Association between collapse and serum creatinine and electrolyte concentrations in marathon runners: a 9-year retrospective study

OBJECTIVE

Abnormal biochemical measurements have previously been described in runners following marathons. The incidence of plasma sodium levels outside the normal range has been reported as 31%, and the incidence of raised creatinine at 30%. This study describes the changes seen in electrolytes and creatinine in collapsed (2010-2019 events) and noncollapsed (during the 2019 event) runners during a UK marathon.

METHODS

Point-of-care sodium, potassium, urea and creatinine estimates were obtained from any collapsed runner treated by the medical team during the Brighton Marathons, as part of their clinical care, and laboratory measurements from control subjects.

RESULTS

Results from 224 collapsed runners were available. Serum creatinine was greater than the normal range in 68.9%. About 6% of sodium results were below, and 3% above the normal range, with the lowest 132 mmol/l. Seventeen percent of potassium readings were above the normal range; the maximum result was 8.4 mmol/l, but 97% were below 6.0 mmol/l. In the control group, mean creatinine was significantly raised in both the collapse and control groups, with 55.4% meeting the criteria for acute kidney injury, but had resolved to baseline after 24 h. Sodium concentration but not the potassium was significantly raised after the race compared with baseline, but only 15% were outside the normal range.

CONCLUSION

In this study, incidence of a raised creatinine was higher than previously reported. However, the significance of such a rise remains unclear with a similar rise seen in collapsed and noncollapsed runners, and resolution noted within 24 h. Abnormal sodium concentrations were observed infrequently, and severely abnormal results were not seen, potentially reflecting current advice to drink enough fluid to quench thirst.

Permanent tattooing has no impact on local sweat rate, sweat sodium concentration and skin temperature or prediction of whole-body sweat sodium concentration during moderate-intensity cycling in a warm environment

PURPOSES

This study investigated the impact of permanently tattooed skin on local sweat rate, sweat sodium concentration and skin temperature and determined whether tattoos alter the relationship between local and whole-body sweat sodium concentration.

METHODS

Thirteen tattooed men (27 ± 6 years) completed a 1 h (66 ± 4% of [Formula: see text]) cycling trial at 32 °C, 35% relative humidity. Sweat rate and sweat sodium concentration were measured using the whole-body washdown and local absorbent patch techniques. Patches and skin-temperature probes were applied over the right/left thighs and tattooed/non-tattooed (contralateral) regions.

RESULTS

Local sweat rates did not differ (p > 0.05) between the right (1.11 ± 0.38) and left (1.21 ± 0.37) thighs and the permanently tattooed (1.93 ± 0.82) and non-tattooed (1.72 ± 0.81 mg cm^-2 min^-1) regions. There were no differences in local sweat sodium concentration between the right (58.2 ± 19.4) and left (55.4 ± 20.3) thighs and the permanently tattooed (73.0 ± 22.9) and non-tattooed (70.2 ± 18.9 mmol L^-1) regions. Difference in local skin temperature between the right and left thighs (- 0.043) was similar to that between the permanently tattooed and non-tattooed (- 0.023 °C) regions. Prediction of whole-body sweat sodium concentration for the permanently tattooed (41.0 ± 6.7) and the non-tattooed (40.2 ± 5.3 mmol L^-1) regions did not differ.

CONCLUSION

Permanent tattoos do not alter local sweat rate, sweat sodium concentration or local skin temperature during moderate-intensity cycling exercise in a warm environment. Results from a patch placed over a tattooed surface correctly predicts whole-body sweat sodium concentration from an equation developed from a non-tattooed region.

Wilderness Medical Society Clinical Practice Guidelines for the Management of Exercise-Associated Hyponatremia: 2019 Update

Exercise-associated hyponatremia (EAH) is defined by a serum or plasma sodium concentration below the normal reference range of 135 mmol·L-1 that occurs during or up to 24 h after prolonged physical activity. It is reported to occur in individual physical activities or during organized endurance events conducted in environments in which medical care is limited and often not available, and patient evacuation to definitive care is often greatly delayed. Rapid recognition and appropriate treatment are essential in the severe form to increase the likelihood of a positive outcome. To mitigate the risk of EAH mismanagement, care providers in the prehospital and in hospital settings must differentiate from other causes that present with similar signs and symptoms. EAH most commonly has overlapping signs and symptoms with heat exhaustion and exertional heat stroke. Failure in this regard is a recognized cause of worsened morbidity and mortality. In an effort to produce best practice guidelines for EAH management, the Wilderness Medical Society convened an expert panel in May 2018. The panel was charged with updating the WMS Practice Guidelines for Treatment of Exercise-Associated Hyponatremia published in 2014 using evidence-based guidelines for the prevention, recognition, and treatment of EAH. Recommendations are made based on presenting with symptomatic EAH, particularly when point-of-care blood sodium testing is unavailable in the field. These recommendations are graded on the basis of the quality of supporting evidence and balanced between the benefits and risks/burdens for each parameter according to the methodology stipulated by the American College of Chest Physicians.

Collapse in the Heat - From Overhydration to the Emergency Room - Three Cases of Exercise-Associated Hyponatremia Associated with Exertional Heat Illness

Exertional heat illness and exercise-associated hyponatremia continue to be a problem in military and recreational events. Symptoms of hyponatremia can be mistaken for heat exhaustion or heat stroke. We describe three cases of symptomatic hyponatremia initially contributed to heat illnesses. The first soldier was a 31-yr-old female who "took a knee" at mile 6 of a 12-mile foot march. She had a core temperature of 100.9°F, a serum sodium level of 129 mmol/L, and drank approximately 4.5 quarts of water in 2 h. The second case was a 27-yr-old female soldier who collapsed at mile 11 of a 12-mile march. Her core temperature was 102.9°F and sodium level was 131 mmol/L. She drank 5 quarts in 2.5 h. The third soldier was a 27-yr-old male who developed nausea and vomiting while conducting an outdoor training event. His core temperature was 98.7°F and sodium level was 125 mmol/L. He drank 6 quarts in 2 h to combat symptoms of heat. All the three cases developed symptomatic hyponatremia by overconsumption of fluids during events lasting less than 3 h. Obtaining point-of-care serum sodium may improve recognition of hyponatremia and guide management for the patient with suspected heat illness and hyponatremia. Depending on severity of symptoms, exercise-associated hyponatremia can be managed by fluid restriction, oral hypertonic broth, or with intravenous 3% saline. Utilizing an ad libitum approach or limiting fluid availability during field or recreational events of up to 3 h may prevent symptomatic hyponatremia while limiting significant dehydration.

Drinking Strategies: Planned Drinking Versus Drinking to Thirst

In humans, thirst tends to be alleviated before complete rehydration is achieved. When sweating rates are high and ad libitum fluid consumption is not sufficient to replace sweat losses, a cumulative loss in body water results. Body mass losses of 2% or greater take time to accumulate. Dehydration of ≥  2% body mass is associated with impaired thermoregulatory function, elevated cardiovascular strain and, in many conditions (e.g., warmer, longer, more intense), impaired aerobic exercise performance. Circumstances where planned drinking is optimal include longer duration activities of >  90 min, particularly in the heat; higher-intensity exercise with high sweat rates; exercise where performance is a concern; and when carbohydrate intake of 1 g/min is desired. Individuals with high sweat rates and/or those concerned with exercise performance should determine sweat rates under conditions (exercise intensity, pace) and environments similar to that anticipated when competing and tailor drinking to prevent body mass losses >  2%. Circumstances where drinking to thirst may be sufficient include short duration exercise of <  1 h to 90 min; exercise in cooler conditions; and lower-intensity exercise. It is recommended to never drink so much that weight is gained.

The effect of hot and cold drinks on thermoregulation, perception, and performance: the role of the gut in thermoreception

PURPOSE

Hot compared to cold drinks alter sweating responses during very low intensity exercise in temperate conditions. The thermoregulatory, perceptual, and performance effects of hot compared to cold drinks in hot, dry conditions during high-intensity exercise have not been examined.

METHOD

Ten participants [mean ± SD characteristics age 25 ± 5 years, height 1.81 ± 0.07 m, body mass 73.5 ± 10.6 kg, maximal power output (P_Max) 350 ± 41 W] completed two conditions, where they drank four boluses (ingested at - 9, 15, 30, and 45 min, respectively) of 3.2 mL kg^- 1 (~ 960 mL total) of either a COLD (5.3 °C) or a HOT drink (49.0 °C), which were contrasted to a no-drink CONTROL. They cycled for 60-min [55% P_Max in hot (34.4 °C) dry (34% RH)] ambient conditions followed by a test to exhaustion (TTE; 80% P_Max). The thermoregulatory, performance, and perceptual implications of drink temperature were measured.

RESULTS

TTE was worse in the CONTROL (170 ± 132 s) than the COLD drink (371 ± 272 s; p = 0.021) and HOT drink conditions (367 ± 301 s; p = 0.038) which were not different (p = 0.965). Sweat responses [i.e., reflex changes in mean skin temperature (T_msk) and galvanic skin conductance] indicated transient reductions in sweating response after COLD drink ingestion. The COLD drink improved thermal comfort beyond the transient changes in sweating.

CONCLUSION

Only COLD drink ingestion changed thermoregulation, but improved perceptual response. Accordingly, we conclude a role for gut thermoreception in thermal perception during exercise in hot, dry conditions.

Intended Hydration Strategies and Knowledge of Exercise-Associated Hyponatraemia in Marathon Runners: A Questionnaire-Based Study

CONTEXT

  Exercise-associated hyponatremia (EAH) is a potentially fatal condition that can be prevented by avoiding excessive fluid intake. Running has become more popular in recent years, so it is important to assess the safety of runners' hydration strategies.

OBJECTIVE

  (1) To explore the intended hydration strategies of a sample of marathon runners before the 2014 London Marathon, (2) to examine their sources of information and knowledge about fluid intake and their understanding of EAH, and (3) to compare these findings with the results of a similar study carried out before the 2010 London Marathon.

DESIGN

  Cross-sectional study.

SETTING

  The 2014 London Marathon.

PATIENTS OR OTHER PARTICIPANTS

  A total of 298 runners (148 males, 150 females), 0.83% of all race finishers.

MAIN OUTCOME MEASURE(S)

  Planned frequency, type, and volume of hydration; sources of information about appropriate drinking; and understanding of hyponatremia were explored. Comparisons were made with data collected from a sample of participants at the 2010 London Marathon. Data relating to the 2014 cohort are presented in descriptive form. Comparisons of the 2010 and 2014 cohorts were conducted using parametric and nonparametric methods.

RESULTS

  A total of 48.7% of the 2014 cohort listed drinking to thirst as the most important factor affecting their hydration strategy during the race. This compared with 25.3% of runners from the 2010 cohort and represented an increase (χ² = 29.1, P = .001); 5.8% of the 2014 cohort planned on drinking more than 3.5 L, compared with 12% of the 2010 cohort (χ² = 4.310, P = .038).

CONCLUSIONS

  The number of sampled individuals using thirst to guide hydration strategies in the 2014 London Marathon increased from 2010. However, more than half of the 2014 cohort was not planning to drink to thirst. Runners still need to be educated about the risks of overdrinking as they continue to demonstrate a lack of knowledge and understanding.

Dehydration: A Multidisciplinary Case-Based Discussion for First-Year Medical Students

INTRODUCTION

As many medical school curricula shift to integrated learning of multiple basic science topics as well as clinical concepts, there is an increasing need for instructional materials that incorporate multiple topics yet are targeted to the knowledge basis of first-year medical students. This interactive case-based session for first-year medical students centers on the clinical presentation and initial evaluation of a patient experiencing dehydration after running a marathon in a high-altitude city.

METHODS

After completion of assigned out-of-class preparation, students followed the patient from a healthy state to moderate dehydration over the course of two 2-hour class sessions. Throughout discussion of the case, students answered questions requiring them to integrate elements of cell biology, biochemistry, physiology, and clinical reasoning with minimal faculty involvement. The learning activity was administered at University of Illinois College of Medicine campuses in both a small-group setting (10 students, one faculty facilitator) and a large-group format (55-90 students, multiple faculty facilitators). Following the activity, we assessed student perceptions of the design and implementation of the materials as well as effectiveness at meeting the learning goals.

RESULTS

Of 198 students who participated in the case discussions on dehydration, the majority rated the case positively, indicated by a rating of good or excellent.

DISCUSSION

This multidisciplinary case on dehydration can be used early in medical education to introduce students to clinical scenarios while learning fundamental science content. An integrated approach to medical content and versatility with regard to class size make this case a valuable teaching tool.

Considerations for Fueling an Endurance Athlete With Home Parenteral Nutrition

The goal of clinicians managing nutrition support for patients with home parenteral nutrition (HPN) is to adapt nutrition needs to best serve the consumers, so they may have the best quality of life despite specialized nutrition needs. Some HPN consumers may desire to participate in endurance athletics, which will require special considerations. This review is intended to outline key nutrition differences in endurance athletes that a nutrition support team should consider when providing HPN.

Systematic review: exercise-induced gastrointestinal syndrome-implications for health and intestinal disease

BACKGROUND

"Exercise-induced gastrointestinal syndrome" refers to disturbances of gastrointestinal integrity and function that are common features of strenuous exercise.

AIM

To systematically review the literature to establish the impact of acute exercise on markers of gastrointestinal integrity and function in healthy populations and those with chronic gastrointestinal conditions.

METHODS

Search literature using five databases (PubMed, EBSCO, Web of Science, SPORTSdiscus, and Ovid Medline) to review publications that focused on the impact of acute exercise on markers of gastrointestinal injury, permeability, endotoxaemia, motility and malabsorption in healthy populations and populations with gastrointestinal diseases/disorders.

RESULTS

As exercise intensity and duration increases, there is considerable evidence for increases in indices of intestinal injury, permeability and endotoxaemia, together with impairment of gastric emptying, slowing of small intestinal transit and malabsorption. The addition of heat stress and running mode appears to exacerbate these markers of gastrointestinal disturbance. Exercise stress of ≥2 hours at 60% VO_2max appears to be the threshold whereby significant gastrointestinal perturbations manifest, irrespective of fitness status. Gastrointestinal symptoms, referable to upper- and lower-gastrointestinal tract, are common and a limiting factor in prolonged strenuous exercise. While there is evidence for health benefits of moderate exercise in patients with inflammatory bowel disease or functional gastrointestinal disorders, the safety of more strenuous exercise has not been established.

CONCLUSIONS

Strenuous exercise has a major reversible impact on gastrointestinal integrity and function of healthy populations. The safety and health implications of prolonged strenuous exercise in patients with chronic gastrointestinal diseases/disorders, while hypothetically worrying, has not been elucidated and requires further investigation.

Nutritional implications for ultra-endurance walking and running events

This paper examines the various nutritional challenges which athletes encounter in preparing for and participating in ultra-endurance walking and running events. Special attention is paid to energy level, performance, and recovery within the context of athletes' intake of carbohydrate, protein, fat, and various vitamins and minerals. It outlines, by way of a review of literature, those factors which promote optimal performance for the ultra-endurance athlete and provides recommendations from multiple researchers concerned with the nutrition and performance of ultra-endurance athletes. Despite the availability of some research about the subject, there is a paucity of longitudinal material which examines athletes by nature and type of ultra-endurance event, gender, age, race, and unique physiological characteristics. Optimal nutrition results in a decreased risk of energy depletion, better performance, and quicker full-recovery.

Water deprivation-partial rehydration induces sensitization of sodium appetite and alteration of hypothalamic transcripts

iSodium intake occurs either as a spontaneous or induced behavior, which is enhanced, i.e., sensitized, by repeated episodes of water deprivation followed by subsequent partial rehydration (WD-PR). In the present work, we examined whether repeated WD-PR alters hypothalamic transcripts related to the brain renin-angiotensin system (RAS) and apelin system in male normotensive Holtzman rats (HTZ). We also examined whether the sodium intake of a strain with genetically inherited high expression of the brain RAS, the spontaneously hypertensive rat (SHR), responds differently than HTZ to repeated WD-PR. We found that repeated WD-PR, besides enhancing spontaneous and induced 0.3 M NaCl intake, increased the hypothalamic expression of angiotensinogen, aminopeptidase N, and apelin receptor transcripts (43%, 60%, and 159%, respectively) in HTZ at the end of the third WD-PR. Repeated WD-PR did not change the daily spontaneous 0.3 M NaCl intake and barely changed the need-induced 0.3 M NaCl intake of SHR. The same treatment consistently enhanced spontaneous daily 0.3 M NaCl intake in the normotensive Wistar-Kyoto rats. The results show that repeated WD-PR produces alterations in hypothalamic transcripts and also sensitizes sodium appetite in HTZ. They suggest an association between the components of hypothalamic RAS and the apelin system, with neural and behavioral plasticity produced by repeated episodes of WD-PR in a normotensive strain. The results also indicate that the inherited hyperactive brain RAS is not a guarantee for sensitization of sodium intake in the male adult SHR exposed to repeated WD-PR.

Wilderness Medical Society practice guidelines for treatment of exercise-associated hyponatremia: 2014 update

Exercise-associated hyponatremia (EAH) is defined by a serum or plasma sodium concentration below the normal reference range of 135 mmol/L that occurs during or up to 24 hours after prolonged physical activity. It is reported to occur in individual physical activities or during organized endurance events conducted in austere environments in which medical care is limited and often not available, and patient evacuation to definitive care is often greatly delayed. Rapid recognition and appropriate treatment are essential in the severe form to ensure a positive outcome. Failure in this regard is a recognized cause of event-related fatality. In an effort to produce best practice guidelines for EAH in the austere environment, the Wilderness Medical Society convened an expert panel. The panel was charged with the development of evidence-based guidelines for management of EAH. Recommendations are made regarding the situations when sodium concentration can be assessed in the field and when these values are not known. These recommendations are graded on the basis of the quality of supporting evidence and balance between the benefits and risks/burdens for each parameter according to the methodology stipulated by the American College of Chest Physicians. This is an updated version of the original WMS Practice Guidelines for Treatment of Exercise-Associated Hyponatremia published in Wilderness & Environmental Medicine 2013;24(3):228-240.

Mapping brain Fos immunoreactivity in response to water deprivation and partial rehydration: Influence of sodium intake

Water deprivation (WD) followed by water intake to satiety, produces satiation of thirst and partial rehydration (PR). Thus, WD-PR is a natural method to differentiate thirst from sodium appetite. WD-PR also produces Fos immunoreactivity (Fos-ir) in interconnected areas of a brain circuit postulated to subserve sodium appetite. In the present work, we evaluated the effect of sodium intake on Fos-ir produced by WD-PR in brain areas operationally defined according to the literature as either facilitatory or inhibitory to sodium intake. Isotonic NaCl was available for ingestion in a sodium appetite test performed immediately after a single episode of WD-PR. Sodium intake decreased Fos-ir in facilitatory areas such as the lamina terminalis (particularly subfornical organ and median preoptic nucleus), central amygdala and hypothalamic parvocellular paraventricular nucleus in the forebrain. Sodium intake also decreased Fos-ir in inhibitory areas such as the area postrema, lateral parabrachial nucleus and nucleus of the solitary tract in the hindbrain. In contrast, sodium intake further increased Fos-ir that was activated by water deprivation in the dorsal raphe nucleus, another inhibitory area localized in the hindbrain. WD-PR increased Fos-ir in the core and shell of the nucleus accumbens. Sodium intake reduced Fos-ir in both parts of the accumbens. In summary, sodium intake following WD-PR reduced Fos-ir in most facilitatory and inhibitory areas, but increased Fos-ir in another inhibitory area. It also reduced Fos-ir in a reward area (accumbens). The results suggest a functional link between sodium intake and the activity of the hindbrain-forebrain circuitry subserving reward and sodium appetite in response to water deprivation.

Hydration Strategy for Endurance Running in an Athlete Requiring Home Parenteral Nutrition

PURPOSE

The purpose of this report is to share our experience with optimizing home parenteral nutrition (HPN) and hydration therapy for an HPN consumer who desired to run a marathon.

METHODS

A 34-year-old woman with idiopathic gastroparesis necessitating HPN and intravenous (IV) hydration desired to train for a marathon. For short runs, prerun and/or postrun hydration were adequate, but a marathon (26.2 miles) would be too long to run without IV hydration. During training, we instructed our consumer to record weights (pre/post run), ambient temperature, running distance, and duration of time. These data were used to calculate her sweat rate and estimate hydration volume during the marathon.

RESULTS

Ambient temperature was a significant factor influencing sweat rate. The estimate temperature for the marathon was 65 °F; therefore, our consumer would have an estimated sweat rate of approximately 720 mL/h. This exceeded the amount of fluid that could be infused during the marathon; therefore, we advised our consumer to overhydrate prior to the race. Initial postrace urine output was low and concentrated but returned to baseline after postrace hydration. Our consumer did not experience any symptoms of dehydration and had only minor muscle soreness.

CONCLUSIONS

Our consumer was able to complete a marathon with IV hydration. We have shown that with careful preparation, calculation, and planning, our HPN consumer was able to adequately maintain her state of hydration and accomplish her goal of running a marathon.

Incidence of Exercise-Associated Hyponatremia and Its Association With Nonosmotic Stimuli of Arginine Vasopressin in the GNW100s Ultra-endurance Marathon

OBJECTIVES

(1) To examine the incidence of exercise-associated hyponatremia (EAH) during and after an ultramarathon and (2) to evaluate hypothesized nonosmotic stimuli [interleukin-6 (IL-6), hypoglycemia, ambient temperature] with arginine vasopressin (AVP) concentrations in hyponatremic versus normonatremic runners.

DESIGN

Prospective cohort study.

SETTING

The Great North Walk 100s ultramarathons.

PARTICIPANTS

Fifteen runners participated in either 103.7- or 173.7-km ultramarathons.

MAIN OUTCOME MEASURES

Serum sodium concentration ([Na]) and AVP concentration. Secondary outcome measures included IL-6, blood glucose, ambient temperature, weight change, fluid consumption, and use of nonsteroidal anti-inflammatory drugs (NSAIDs).

RESULTS

Postrace EAH incidence was 4 of 15 runners, whereas EAH incidence at any point during the race was in 10 of 15 runners. A significant positive correlation was noted between AVP and IL-6 (r = 0.31, P < 0.05) but not between AVP and blood glucose (r = 0.09, nonsignificant) or ambient temperature (r = -0.12, NS). Subgroup analysis revealed that the correlation between AVP and IL-6 was significant in hyponatremic (r = 0.37, P < 0.05) but not normonatremic runners (r = 0.31, NS). Hyponatremic runners lost less weight than normonatremic runners (2.5 vs. 3.7 kg, P < 0.05, respectively) despite similar fluid consumption. Seven of 10 hyponatremic runners consumed NSAIDs versus 0 of 5 normonatremic runners.

CONCLUSIONS

Exercise-associated hyponatremia incidence mid-race is higher than postrace, suggesting that 40% of runners are able to self-correct low serum [Na] status during an ultramarathon. Interleukin-6 seems to be the main nonosmotic stimulus associated with AVP in hyponatremic runners. Nonsteroidal anti-inflammatory ingestion is more common in hyponatremic versus normonatremic runners.

CLINICAL RELEVANCE

Exercise-associated hyponatremia associated with nonosmotic AVP secretion may be more common during ultramarathon races without discriminatory clinical symptomatology.

Nutrition habits in 24-hour mountain bike racers

We investigated seventy-four ultra-mountain bikers (MTBers) competing in the solo category in the first descriptive field study to detail nutrition habits and the most common food before during and after the 24 hour race using questionnaires. During the race, bananas (86.5%), energy bars (50.0%), apples (43.2%) and cheese (43.2%) were the most commonly consumed food, followed by bread (44.6%), rice (33.8%) and bananas (33.8%) after the race. Average fluid intake was 0.5 ± 0.2 l/h. The main beverage was isotonic sports drink (82.4%) during and pure water (66.2%) after the race. The most preferred four supplements in the four weeks before, the day before, during and after the race were vitamin C (35.1%), magnesium (44.6%), magnesium (43.2%) and branched-chain amino acids (24.3%), respectively. Total frequency of food intake (30.6 ± 10.5 times/24 hrs) was associated with fluid intake (r = 0.43, P = 0.04) and both were highest at the beginning of the race and lower during the night hours and the last race segment in a subgroup of twenty-three ultra-MTBers. Supplement intake frequency (6.8 ± 8.4 times/24 hrs) was highest during the night hours and lower at the beginning and end of the race. Elevated food and fluid intake among participants tracked across all race segments (P < 0.001). In conclusion, the nutrition strategy employed by ultra-MTBers was similar to those demonstrated in previous studies of ultra-cyclists with some exceptions among selected individuals.

Energy drinks: Getting wings but at what health cost?

Energy drink consumption represents a global public health problem, especially among adolescents and young adults. The consumption of energy drinks has seen a substantial increase during the past few decades, especially in the Western and Asian countries. Although manufacturers of energy drinks claim that these beverages are beneficial in that they can boost energy, physical performance, and improve cognitive performance, there is insufficient scientific evidence to support these claims. The known and unknown pharmacology of the constituents of energy drinks, supplemented with reports of toxicity, raise concern for the potentially severe adverse events linked with energy drink use. Limited numbers of reviews have been published on this important subject..The aim of this review was to identify the major ingredients in energy drinks and to delineate the adverse effects related to their consumption.

Methods: Electronic databases of PubMed, Clinical Key, and Google and Cochrane library were extensively searched for energy drink articles. More than hundred articles were reviewed, scrutinized and critically appraised and the most relevant forty articles were used

Conclusion: Energy drinks & its ingredients are potentially dangerous to many aspects of health. Measures should be taken to improve awareness among adolescents and their parents regarding the potential hazards of energy drinks. Furthermore, the sale of energy drinks on college and university campuses and to adolescents below 16 years should be prohibited.

Effects of 100-km ultramarathon on acute kidney injury

OBJECTIVE

To evaluate the prevalence and characteristics of acute kidney injury (AKI) in 100-km ultramarathon runners.

DESIGN

Prospective observational study.

SETTING

The 2011 Soochow University ultramarathon, in which each athlete ran for 100 km.

PARTICIPANTS

All Taiwanese entrants who participated in the 100-km race and lived in the northern part of Taiwan were invited to participate in the study.

MAIN OUTCOME MEASURES

Acute kidney injury was defined using the Acute Kidney Injury Network criteria. Blood and urine samples were collected 1 week before, immediately after, and 1 day after the race.

RESULTS

Immediately after the race, 85% (22) of the 26 subjects were diagnosed with AKI, 65% (16) with moderate dehydration, 23% (6) with muscle cramps, and 12% (3) with hematuria. Body weight was significantly decreased from prerace to all postrace measurements. Plasma levels of potassium ion, creatinine, renin, and aldosterone were significantly elevated immediately after the race and then significantly reduced 1 day after the race. Changes in plasma levels of sodium, creatine kinase, and creatine kinase-MB, as well as urine potassium and creatinine, were indicative of AKI.

CONCLUSIONS

Transient AKI and muscle cramps are very common in 100-km ultramarathon runners. All transient ultra-runners who developed AKI in this study recovered their renal function 1 day later.

CLINICAL RELEVANCE

Ultramarathon running is associated with a wide range of significant changes in hematological parameters, several of which can be associated with potentially serious renal and physiological abnormalities.

A variant within the AQP1 3'-untranslated region is associated with running performance, but not weight changes, during an Ironman Triathlon

The objective of this study was to test the association of the rs1049305 (G > C) variant within the 3'-untranslated region of the aquaporin 1 gene, AQP1, with changes in body weight, post-race serum sodium concentration and performance in Ironman triathletes. Five hundred and four male Ironman triathletes were genotyped for the rs1049305 variant within the AQP1 gene. Change in pre- and post-race body weight was calculated for 470 triathletes and used as a proxy for changes in body fluid during the race, as well as to divide triathletes into biologically relevant weight-loss groups (0-3%, 3-5% and >5%). There were no rs1049305 genotype effects on post-race serum sodium concentrations (P = 0.647), pre-race weight (P = 0.610) nor relative weight change during the Ironman Triathlons (P = 0.705). In addition, there were no significant differences in genotype (P = 0.640) nor allele (P = 0.643) distributions between the weight loss groups. However, triathletes who carry a C-allele were found to complete the 42.2-km run stage faster (mean 286, s = 49 min) than triathletes with a GG genotype (mean 296, s = 47 min; P = 0.032). The AQP1 rs1049305 variant is associated with running performance, but not relative body weight change, during the 2000, 2001 and 2006 South African Ironman Triathlons.

Are we being drowned in hydration advice? Thirsty for more?

Hydration pertains simplistically to body water volume. Functionally, however, hydration is one aspect of fluid regulation that is far more complex, as it involves the homeostatic regulation of total body fluid volume, composition and distribution. Deliberate or pathological alteration of these regulated factors can be disabling or fatal, whereas they are impacted by exercise and by all environmental stressors (e.g. heat, immersion, gravity) both acutely and chronically. For example, dehydration during exercising and environmental heat stress reduces water volume more than electrolyte content, causing hyperosmotic hypohydration. If exercise continues for many hours with access to food and water, composition returns to normal but extracellular volume increases well above baseline (if exercising upright and at low altitude). Repeating bouts of exercise or heat stress does likewise. Dehydration due to physical activity or environmental heat is a routine fluid-regulatory stress. How to gauge such dehydration and - more importantly-what to do about it, are contested heavily within sports medicine and nutrition. Drinking to limit changes in body mass is commonly advocated (to maintain ≤2% reduction), rather than relying on behavioural cues (mainly thirst) because the latter has been deemed too insensitive. This review, as part of the series on moving in extreme environments, critiques the validity, problems and merits of externally versus autonomously controlled fluid-regulatory behaviours, both acutely and chronically. Our contention is that externally advocated hydration policies (especially based on change in body mass with exercise in healthy individuals) have limited merit and are extrapolated and imposed too widely upon society, at the expense of autonomy. More research is warranted to examine whether ad libitum versus avid drinking is beneficial, detrimental or neither in: acute settings; adapting for obligatory dehydration (e.g. elite endurance competition in the heat), and; development of chronic diseases that are associated with an extreme lack of environmental stress.

Drinking to thirst versus drinking ad libitum during road cycling

CONTEXT

The sensation of thirst is different from the complex behavior of drinking ad libitum. Rehydration recommendations to athletes differ, depending on the source, yet no previous researchers have systematically compared drinking to thirst (D(TT)) versus ad libitum drinking behavior (D(AL)).

OBJECTIVE

To compare 2 groups of trained cyclists (D(TT) and D(AL)) who had similar physical characteristics and training programs (P > .05). The D(TT) group (n = 12, age = 47 ± 7 years) drank only when thirsty, whereas the D(AL) group (n = 12, age = 44 ± 7 years) consumed fluid ad libitum (ie, whenever and in whatever volume desired).

DESIGN

Cohort study.

SETTING

Road cycling (164 km) in the heat (36.1 °C ± 6.5 °C).

PATIENTS OR OTHER PARTICIPANTS

Ultraendurance cyclists (4 women, 20 men).

INTERVENTION(S)

We recorded measurements 1 day before the event, on event day before the start, at 3 roadside aid stations, at the finish line, and 1 day after the event.

MAIN OUTCOME MEASURE(S)

Body mass, urinary hydration indices, and food and fluids consumed.

RESULTS

No between-groups differences were seen on event day for total exercise time (DTT = 6.69 ± 0.89 hours, DAL = 6.66 ± 0.77 hours), urinary indices (specific gravity, color), body mass change (D(TT) = -2.22% ± 1.73%, DAL = -2.29% ± 1.62%), fluid intake (D(TT) = 5.63 ± 2.59 L/6.7 h, D(AL) = 6.04 ± 2.37 L/6.7 h), dietary energy intake, macronutrient intake, ratings of thirst (D(TT) start = 2 ± 1, D(TT) finish = 6 ± 1, DAL start = 2 ± 1, D(AL) finish = 6 ± 1), pain, perceived exertion, or thermal sensation. Total fluid intake on recovery day +1 was the primary significant difference (D(AL) = 5.13 ± 1.87 L/24 h, D(TT) = 3.13 ± 1.53 L/24 h, t18 = 2.59, P = .02).

CONCLUSIONS

Observations on event day indicated that drinking to thirst and drinking ad libitum resulted in similar physiologic and perceptual outcomes. This suggests that specific instructions to "drink to thirst" were unnecessary. Indeed, if athletes drink ad libitum, they can focus on training and competition rather than being distracted by ongoing evaluation of thirst sensations.

Changes in foot volume, body composition, and hydration status in male and female 24-hour ultra-mountain bikers

BACKGROUND

The effects of running and cycling on changes in hydration status and body composition during a 24-hour race have been described previously, but data for 24-hour ultra-mountain bikers are missing. The present study investigated changes in foot volume, body composition, and hydration status in male and female 24-hour ultra-mountain bikers.

METHODS

We compared in 49 (37 men and 12 women) 24-hour ultra-mountain bikers (ultra-MTBers) changes (Δ) in body mass (BM). Fat mass (FM), percent body fat (%BF) and skeletal muscle mass (SM) were estimated using anthropometric methods. Changes in total body water (TBW), extracellular fluid (ECF) and intracellular fluid (ICF) were determined using bioelectrical impedance and changes in foot volume using plethysmography. Haematocrit, plasma [Na+], plasma urea, plasma osmolality, urine urea, urine specific gravity and urine osmolality were measured in a subgroup of 25 ultra-MTBers (16 men and 9 women).

RESULTS

In male 24-hour ultra-MTBers, BM (P < 0.001), FM (P < 0.001), %BF (P < 0.001) and ECF (P < 0.05) decreased whereas SM and TBW did not change (P > 0.05). A significant correlation was found between post-race BM and post-race FM (r = 0.63, P < 0.001). In female ultra-MTBers, BM (P < 0.05), %BF (P < 0.05) and FM (P < 0.001) decreased, whereas SM, ECF and TBW remained stable (P > 0.05). Absolute ranking in the race was related to Δ%BM (P < 0.001) and Δ%FM in men (P < 0.001) and to Δ%BM (P < 0.05) in women. In male ultra-MTBers, increased post-race plasma urea (P < 0.001) was negatively related to absolute ranking in the race, Δ%BM, post-race FM and Δ%ECF (P < 0.05). Foot volume remained stable in both sexes (P > 0.05).

CONCLUSIONS

Male and female 24-hour ultra-MTBers experienced a significant loss in BM and FM, whereas SM remained stable. Body weight changes and increases in plasma urea do not reflect a change in body hydration status. No oedema of the lower limbs occurred.

The prevalence of exercise-associated hyponatremia in 24-hour ultra-mountain bikers, 24-hour ultra-runners and multi-stage ultra-mountain bikers in the Czech Republic

BACKGROUND

To assess the prevalence of exercise-associated hyponatremia (EAH) in two 24-hour mountain bike (MTB) (R1,R2), one 24-hour running (R3) and one multi-stage MTB (R4) races held in the Czech Republic in a cluster of four cross-sectional studies.

METHODS

In 27 ultra-mountain bikers (ultra-MTBers), 12 ultra-runners, and 14 multi-stage MTBers, fluid intake, changes (Δ) in body mass, hematocrit, plasma volume, plasma [Na+], plasma [K+], plasma osmolality, urine [Na+], urine [K+], urine specific gravity, urine osmolality, K+/Na+ ratio in urine, transtubular potassium gradient and glomerular filtration rate were measured and calculated. The use of non-steroidal anti-inflammatory drugs and symptoms of EAH were recorded using post-race questionnaires.

RESULTS

Of the 53 finishers, three (5.7%) developed post-race EAH, thereof one (3.7%) ultra-MTBer, one (8.3%) ultra-runner and one (7.1%) multi-stage MTBer. Plasma [Na+] decreased significantly (p < 0.001) only in R4. Urine osmolality (R1, R3, R4 p < 0.001; R2 p < 0.05) and glomerular filtration rate (p < 0.001) increased, and body mass decreased in all races (p < 0.05). Δ body mass was inversely related to the number of kilometers achieved (p < 0.001) in R2 where better ultra-MTBers tended to lose more weight. Δ body mass (p < 0.001) and %Δ body mass (p = 0.05) were positively related to lower post-race plasma [Na+] in R3 that was associated with increased loss in body mass. Fluid intake was positively related to race performance in R1 and R2 (R1: p = 0.04; R2: p = 0.01) where ultra-MTBers in R1 and R2 who drank more finished ahead of those who drank less. Post-race plasma [Na+] was negatively associated with race performance in ultra-MTBers in R2 (p < 0.05), similarly ultra-runners in R3 (p < 0.05) where finishers with more kilometres had lower post-race plasma [Na+].

CONCLUSIONS

The prevalence of EAH in the Czech Republic was no higher compared to existing reports on ultra-endurance athletes in other countries. Lower plasma [Na+] and development of EAH may be attributed to overdrinking, a pituitary secretion of vasopressin, an impaired mobilization of osmotically inactive sodium stores, and/or an inappropriate inactivation of osmotically active sodium.

24-h fluid kinetics and perception of sweat losses following a 1-h run in a temperate environment

This study examined 24-h post-run hydration status and sweat loss estimation accuracy in college age runners (men=12, women=8) after completing a 1-h self-paced outdoor run (wet bulb globe temperature=19.9±3.0 °C). Sweat losses (1353±422 mL; 1.9%±0.5% of body mass) were significantly greater (p<0.001) than perceived losses (686±586 mL). Cumulative fluid consumption equaled 3876±1133 mL (218±178 mL during) with 37% of fluid ingested lost through urine voids (1450±678 mL). Fluid balance based on intake and urine production equaled +554±669 mL at 12 h and +1186±735 mL at 24 h. Most runners reported euhydrated (pre-run urine specific gravity (USG)=1.018±0.008) with no changes (p=0.33) at hours 12 or 24 when both genders were included. However, USG was higher (p=0.004) at 12 h post-run for men (1.025±0.0070 vs. 1.014±0.007), who consumed 171%±40% of sweat losses at 12 h vs. 268%±88% for women. Most runners do not need intervention concerning between bout hydration needs in temperate environments. However, repeated USG measurements were able to identify runners who greatly under or over consumed fluid during recovery. Practitioners can use multiple USG assessments as cheap method to detect runners who need to modify their hydration strategies and should promote assessment of sweat losses by change in body mass, as runners had poor perception of sweat losses.

The effect of physiology and hydration beliefs on race behavior and postrace sodium in 161-km ultramarathon finishers

PURPOSE

To determine if beliefs about physiology and rehydration affect ultramarathon runners' hydration behaviors or if these beliefs increase the risk for exercise-associated hyponatremia (EAH).

METHODS

Participants of the 2011 161-km Western States Endurance Run completed a prerace questionnaire, prerace and postrace body-mass measurements, and postrace assessment of serum sodium ([Na⁺]).

RESULTS

Of 310 finishers, 309 (99.7%) completed the prerace questionnaire and 207 (67%) underwent postrace blood studies. Twelve (5.8%) finishers had asymptomatic EAH ([Na⁺] range 131-134 mmol/L). The most common hydration plan (43.1%) was drinking according to schedule, and these runners did so to replace fluid lost when sweating (100%) and to avoid dehydration (81.2%). Prerace drinking plan was not associated with postrace [Na⁺] or the development of postrace hyponatremia. There also were no group differences between those with and those without EAH for any other variables including planned energy intake or knowledge of fluid balance. Runners not planning to drink to thirst trended toward more influence from advertisements (P = .056) and were significantly more influenced by scientific organizations (P = .043) than runners with other drinking plans. Finally, runners who believe that EAH is caused by excessive drinking adopted a lower-volume drinking plan (P = .005), while runners who believe that EAH is caused by sodium loss via sweating reported more common use of sodium supplementation during the race (P = .017).

CONCLUSIONS

Beliefs regarding the causes of EAH alter race behaviors including drinking plan and sodium supplementation but do not appear to affect the likelihood of developing EAH during a 161-km ultramarathon.

Water and sodium intake habits and status of ultra-endurance runners during a multi-stage ultra-marathon conducted in a hot ambient environment: an observational field based study

Background

Anecdotal evidence suggests ultra-runners may not be consuming sufficient water through foods and fluids to maintenance euhydration, and present sub-optimal sodium intakes, throughout multi-stage ultra-marathon (MSUM) competitions in the heat. Subsequently, the aims were primarily to assess water and sodium intake habits of recreational ultra-runners during a five stage 225 km semi self-sufficient MSUM conducted in a hot ambient environment (T_max range: 32°C to 40°C); simultaneously to monitor serum sodium concentration, and hydration status using multiple hydration assessment techniques.

Methods

Total daily, pre-stage, during running, and post-stage water and sodium ingestion of ultra-endurance runners (UER, n = 74) and control (CON, n = 12) through foods and fluids were recorded on Stages 1 to 4 by trained dietetic researchers using dietary recall interview technique, and analysed through dietary analysis software. Body mass (BM), hydration status, and serum sodium concentration were determined pre- and post-Stages 1 to 5.

Results

Water (overall mean (SD): total daily 7.7 (1.5) L/day, during running 732 (183) ml/h) and sodium (total daily 3.9 (1.3) g/day, during running 270 (151) mg/L) ingestion did not differ between stages in UER (p < 0.001 vs. CON). Exercise-induced BM loss was 2.4 (1.2)% (p < 0.001). Pre- to post-stage BM gains were observed in 26% of UER along competition. Pre- and post-stage plasma osmolality remained within normal clinical reference range (280 to 303 mOsmol/kg) in the majority of UER (p > 0.05 vs. CON pre-stage). Asymptomatic hyponatraemia (<135 mmol/L) was evident pre- and post-stage in n = 8 UER, corresponding to 42% of sampled participants. Pre- and post-stage urine colour, urine osmolality and urine/plasma osmolality ratio increased (p < 0.001) as competition progressed in UER, with no change in CON. Plasma volume and extra-cellular water increased (p < 0.001) 22.8% and 9.2%, respectively, from pre-Stage 1 to 5 in UER, with no change in CON.

Conclusion

Water intake habits of ultra-runners during MSUM conducted in hot ambient conditions appear to be sufficient to maintain baseline euhydration levels. However, fluid over-consumption behaviours were evident along competition, irrespective of running speed and gender. Normonatraemia was observed in the majority of ultra-runners throughout MSUM, despite sodium ingestion under benchmark recommendations.

[Hyponatremic encephalopathy with non-cardiogenic pulmonary edema. Development following marathon run]

This article presents the case of a 52-year-old woman who developed exercise-associated hyponatremia (EAH) complicated by non-cardiogenic pulmonary edema after a marathon run. The condition of EAH is a potentially life-threatening complication of endurance exercise. The main cause seems to be inadequate intake of free water during or following exercise with enduring antidiuresis due to nonosmotic stimulation of ADH secretion. Known risk factors are female gender, slow running pace and lack of weight loss. Emergency therapy is fluid restriction and bolus infusion of 3% NaCl solution to rapidly reduce brain edema.

Half-marathon and full-marathon runners' hydration practices and perceptions

CONTEXT

The behaviors and beliefs of recreational runners with regard to hydration maintenance are not well elucidated.

OBJECTIVE

To examine which beverages runners choose to drink and why, negative performance and health experiences related to dehydration, and methods used to assess hydration status.

DESIGN

Cross-sectional study.

SETTING

Marathon registration site.

PATIENTS OR OTHER PARTICIPANTS

Men (n = 146) and women (n = 130) (age = 38.3 ± 11.3 years) registered for the 2010 Little Rock Half-Marathon or Full Marathon.

INTERVENTION(S)

A 23-item questionnaire was administered to runners when they picked up their race timing chips.

MAIN OUTCOME MEASURE(S)

Runners were separated into tertiles (Low, Mod, High) based on z scores derived from training volume, expected performance, and running experience. We used a 100-mm visual analog scale with anchors of 0 (never) and 100 (always). Total sample responses and comparisons between tertile groups for questionnaire items are presented.

RESULTS

The High group (58±31) reported greater consumption of sport beverages in exercise environments than the Low (42 ± 35 mm) and Mod (39 ± 32 mm) groups (P < .05) and perceived sport beverages to be superior to water in meeting hydration needs (P < .05) and improving performance during runs greater than 1 hour (P < .05). Seventy percent of runners experienced 1 or more incidents in which they believed dehydration resulted in a major performance decrement, and 45% perceived dehydration to have resulted in adverse health effects. Twenty percent of runners reported monitoring their hydration status. Urine color was the method most often reported (7%), whereas only 2% reported measuring changes in body weight.

CONCLUSIONS

Greater attention should be paid to informing runners of valid techniques to monitor hydration status and developing an appropriate individualized hydration strategy.

Exertional Heat Stroke – The Athlete's Nemesis

Heat stroke represents the extreme end of a spectrum of heat-related illnesses. It can occur in endurance athletes. Its incidence is probably under-reported. Patients present confused, drowsy or comatose, with a raised core temperature, but often a falsely reassuring peripheral temperature. Treatment is centred on reducing the core temperature as rapidly as possible and appropriate supportive management. Even with prompt treatment, it is associated with multi-organ dysfunction and death. Patients are often misdiagnosed, or diagnosed late. This is probably exacerbated by a wide differential diagnosis, the need for a core temperature measurement to reach the diagnosis and clinicians being unfamiliar with the disease. The need for immediate recognition, and immediate treatment compounds the problem. Survivors may experience long-term neurological disability and may be at risk of a further episode. Patients should return to sport gradually and only when they feel well. Its epidemiology, pathophysiology and clinical management are reviewed.

Lack of awareness of fluid needs among participants at a midwest marathon

BACKGROUND

Marathon running has become popular, particularly among inexperienced runners.

HYPOTHESIS

Many marathoners are inexperienced and lack concern for potential complications of marathon running.

STUDY DESIGN

Cross-sectional survey.

METHODS

In sum, 419 runners completed a survey on a variety of topics regarding training for a marathon and hydration strategies.

RESULTS

Overall, 211 females (38.3 ± 9.1 years old) and 208 males (41.6 ± 11.0 years old) participated. They trained for 6.8 ± 4.3 months and had run for 9.8 ± 9.1 years; 33.5% had no marathon experience and 16.9% had run 1 marathon. Of the injuries reported, 77.6% and 72.9% were minor musculoskeletal injuries during the current and previous running seasons, respectively. Of the 278 runners who had run a marathon, 54 (19.0%) had been treated in the medical tent, 31.5% of whom for dehydration. Furthermore, 54.9% and 64.3% of the survey participants were "not at all" concerned with musculoskeletal injury and hyponatremia, respectively. Also, 88.7% did not know their sweat rate; 67.8% did not weigh themselves; and 81.3% had no other method of hydration assessment. No significant correlations were found between concern for hyponatremia and age, sex, or experience.

CONCLUSIONS

Most participants were inexperienced, lacked concern for injury or hyponatremia, and were not using methods of hydration assessment.

Ad libitum fluid intake leads to no leg swelling in male Ironman triathletes - an observational field study

BACKGROUND

An association between fluid intake and limb swelling has been described for 100-km ultra-marathoners. We investigated a potential development of peripheral oedemata in Ironman triathletes competing over 3.8 km swimming, 180 km cycling and 42.2 km running.

METHODS

In 15 male Ironman triathletes, fluid intake, changes in body mass, fat mass, skeletal muscle mass, limb volumes and skinfold thickness were measured. Changes in renal function, parameters of skeletal muscle damage, hematologic parameters and osmolality in both serum and urine were determined. Skinfold thicknesses at hands and feet were measured using LIPOMETER® and changes of limb volumes were measured using plethysmography.

RESULTS

The athletes consumed a total of 8.6 ± 4.4 L of fluids, equal to 0.79 ± 0.43 L/h. Body mass, skeletal muscle mass and the volume of the lower leg decreased (p <0.05), fat mass, skinfold thicknesses and the volume of the arm remained unchanged (p >0.05). The decrease in skeletal muscle mass was associated with the decrease in body mass (p <0.05). The decrease in the lower leg volume was unrelated to fluid intake (p >0.05). Haemoglobin, haematocrit and serum sodium remained unchanged (p >0.05). Osmolality in serum and urine increased (p <0.05). The change in body mass was related to post-race serum sodium concentration ([Na+]) (r = -0.52, p <0.05) and post-race serum osmolality (r = -0.60, p <0.05).

CONCLUSIONS

In these Ironman triathletes, ad libitum fluid intake maintained plasma [Na+] and plasma osmolality and led to no peripheral oedemata. The volume of the lower leg decreased and the decrease was unrelated to fluid intake. Future studies may investigate ultra-triathletes competing in a Triple Iron triathlon over 11.4 km swimming, 540 km cycling and 126.6 km running to find an association between fluid intake and the development of peripheral oedemata.

Intravenous fluid use in athletes

CONTEXT

Time allowing, euhydration can be achieved in the vast majority of individuals by drinking and eating normal beverages and meals. Important to the competitive athlete is prevention and treatment of dehydration and exercise-associated muscle cramps, as they are linked to a decline in athletic performance. Intravenous (IV) prehydration and rehydration has been proposed as an ergogenic aid to achieve euhydration more effectively and efficiently.

EVIDENCE ACQUISITION

PubMed database was searched in November 2011 for all English-language articles related to IV utilization in sport using the keywords intravenous, fluid requirements, rehydration, hydration, athlete, sport, exercise, volume expansion, and performance.

RESULTS

Limited evidence exists for prehydration with IV fluids. Although anecdotal evidence does exist, at this time there are no high-level studies confirming that IV prehydration prevents dehydration or the onset of exercise-associated muscle cramps. Currently, there are no published studies describing IV fluid use during the course of an event, at intermission, or after the event as an ergogenic aid.

CONCLUSION

The use of IV fluid may be beneficial for a subset of fluid-sensitive athletes; this should be reserved for high-level athletes with strong histories of symptoms in well-monitored settings. Volume expanders may also be beneficial for some athletes. IV fluids and plasma binders are not allowed in World Anti-Doping Agency-governed competitions. Routine IV therapy cannot be recommended as best practice for the majority of athletes.