Jonathan P. Dugas

Consensus statement of the 1st International Exercise-Associated Hyponatremia Consensus Development Conference, Cape Town, South Africa 2005.

Over the past decade, exercise-associated hyponatremia (EAH) has emerged as an important complication of prolonged endurance activity. Prior to 1985, this condition was not reported, and runners generally finished marathons with weight loss but without serious medical complications. Abnormalities of serum sodium concentrations ([Na]), when measured, were confined to elevated levels consistent with varying degrees of volume depletion. In March 2005, a panel of twelve international experts on exercise physiology, sport medicine, water metabolism and body fluid homeostasis convened in Cape Town, South Africa, for the 1st International Exercise-Associated Hyponatremia Consensus Development Conference. The primary goal of this panel was to review all of the existing data on EAH and formulate an evidence-based analysis that would define the current understanding of the pathophysiology of EAH. In particular, the panel was constituted to facilitate integration of existing medical and scientific knowledge of other forms of hyponatremia with the occurrence of this homeostatic imbalance during endurance exercise. A secondary goal of the EAH Consensus Development Conference was to prepare a statement that would serve to curtail the growing problem of EAH by disseminating the most current information to both medical personnel and the greater public on the prevalence, nature and treatment of this disorder. The panel strived to clearly articulate what we agreed upon, debate issues that we did not agree upon, and describe in detail what we did and did not know, including minority viewpoints that were supported by clinical and experimental data. The following statement reflects a concise summary of the data deliberated and synthesized by the panel and provides a ‘‘snapshot in time’’ of the current state of knowledge on EAH. New knowledge will continue to advance regarding our understanding of EAH, and will mandate future updates to this consensus statement.

Conjugated linoleic acid versus high-oleic acid sunflower oil: effects on energy metabolism, glucose tolerance, blood lipids, appetite and body composition in regularly exercising individuals

The aim of this study was to measure the effects of 12 weeks of conjugated linoleic acid (CLA) supplementation on body composition, RER, RMR, blood lipid profiles, insulin sensitivity and appetite in exercising, normal-weight persons. In this double-blind, randomised, controlled trial, sixty-two non-obese subjects (twenty-five men, thirty-seven women) received either 3.9 g/d CLA or 3.9 g high-oleic acid sunflower oil for 12 weeks. Prior to and after 12 weeks of supplementation, oral glucose tolerance, blood lipid concentrations, body composition (dual-energy X-ray absorptiometry and computerised tomography scans), RMR, resting and exercising RER and appetite were measured. There were no significant effects of CLA on body composition or distribution, RMR, RER or appetite. During the oral glucose tolerance tests, mean plasma insulin concentrations (0, 30, 120 min) were significantly lower (P= 0.04) in women who supplemented with CLA (24.3 (SD 9.7) to 20.4 (SD 8.5) microU/ml) compared to high-oleic acid sunflower oil control (23.7 (SD 9.8) to 26.0 (SD 8.8) microU/ml). Serum NEFA levels in response to oral glucose were attenuated in both men and women in the CLA (P=0.001) compared to control group. However, serum total cholesterol and LDL-cholesterol concentrations decreased in both groups and HDL-cholesterol concentrations decreased in women over 12 weeks (P=0.001, P=0.02, P=0.02, respectively). In conclusion, mixed-isomer CLA supplementation had a favourable effect on serum insulin and NEFA response to oral glucose in non-obese, regularly exercising women, but there were no CLA-specific effects on body composition, energy expenditure or appetite.

Beliefs about hydration and physiology drive drinking behaviours in runners

Background Exercise-associated hyponatraemia (EAH) is a dilutional hyponatraemia that is caused primarily by the intake of hypotonic fluid beyond the dictates of thirst and exacerbated by the syndrome of inappropriate antidiuretic hormone secretion as well as an inability to mobilise osmotically inactive sodium stores. Runners who drink more than to their thirst do so for a reason, and understanding and curtailing this behaviour will probably decrease the incidence of this highly preventable condition. Objective To determine the beliefs about fluid replacement held by runners and whether these beliefs are reflected in hydration behaviours. Methods An online survey was filled out by 197 runners solicited by personal solicitation, e-mail and flyers distributed at three local races in autumn 2009. Results Most runners (58%) drink only when thirsty. Runners drinking to a set schedule are significantly older, more experienced and faster than those drinking when thirsty. Gastrointestinal distress is the most frequently cited (71.5%) reason to avoid overhydration. Runners have a poor understanding of the physiological consequences of hydration behaviours that frequently reflect messages of advertising. Conclusions Runners at highest risk of EAH exhibit behaviour that is shaped by their beliefs about the benefits and risks of hydration. These beliefs are frequently based on misconceptions about basic exercise physiology.

Changes in plasma arginine vasopressin concentrations in cyclists participating in a 109-km cycle race

Objective To evaluate the osmotic and non-osmotic regulation of arginine vasopressin (AVP) during endurance cycling. Design Observational study. Setting 109 km cycle race. Participants 33 Cyclists. Interventions None. Main outcome measurements Plasma sodium concentration ([Na+]), plasma volume (PV) and plasma arginine vasopressin (AVP) concentration ([AVP]p). Results A fourfold increase in [AVP]p occurred despite a 2-mmol l−1 decrease in plasma [Na+] combined with only modest (5%) PV contraction. A significant inverse correlation was noted between [AVP]p Δ and urine osmolality Δ (r = −0.41, p<0.05), whereas non-significant inverse correlations were noted between [AVP]p and both plasma [Na+] Δ and % PV Δ. Four cyclists finished the race with asymptomatic hyponatraemia. The only significant difference between the entire cohort with this subset of athletes was postrace plasma [Na+] (137.7 vs 133.5 mmol l−1, p<0.001) and plasma [Na+] Δ (−1.9 vs −5.1 mmol l−1, p<0.05). The mean prerace [AVP]p of these four cyclists was just below the minimum detectable limit (0.3 pg ml−1) and increased marginally (0.4 pg ml−1) despite the decline in plasma [Na+]. Conclusions The osmotic regulation of [AVP]p during competitive cycling was overshadowed by non-osmotic AVP secretion. The modest decrease in PV was not the primary non-osmotic stimulus to AVP. Partial suppression of AVP occurred in four (12%) cyclists who developed hyponatraemia during 5 h of riding. Therefore, these results confirm that non-osmotic AVP secretion and exercise-associated hyponatraemia does, in fact, occur in cyclists participating in a 109 km cycle race. However, the stimuli to AVP is likely different between cycling and running.

Dysnatremia predicts a delayed recovery in collapsed ultramarathon runners.

Objective:To assess (1) the incidence of dysnatremia in collapsed runners presenting to the medical tent of the 89-km Comrades Marathon and whether dysnatremia influences time to discharge, and (2) whether intravenous fluids could restore serum sodium concentration ([Na+]) to 140 mM faster than could the administration of oral fluids. Design:Prospective randomized controlled trial. Setting:2005 Comrades Marathon. Participants:One hundred thirty-three collapsed runners and 31 control-group runners. Interventions:Collapsed runners presenting to the medical tent at the finish of the 2005 Comrades Marathon were randomized into an intravenous or oral fluid administration group, with the type and amount of fluid administered dictated by initial [Na+]. Main Outcome Measures:Time to discharge, serum [Na+]. Results:Forty-five percent of collapsed runners were hypernatremic, 2% were hyponatremic, and 53% were normonatremic. Normonatremic runners spent significantly less time in the medical tent (80 ± 31 minutes) compared with hypernatremic (102 ± 36 minutes) and hyponatremic (146 ± 122 minutes) runners. Intravenous fluid therapy produced larger but nonsignificant reductions in [Na+] than oral therapy (−2.1 ± 3.1 versus −0.7 ± 1.8 mM); however, 45% of runners assigned to the oral fluid group could not tolerate oral rehydration. Conclusions:A slight majority of collapsed runners were normonatremic and spent significantly less time in the medical tent compared with hyper- and hyponatremic athletes. Initial rates of correction of hypernatremia were similar with intravenous and oral hypotonic fluid therapy. Clinicians should be advised that intravenous fluid resuscitation may best benefit hypernatremic collapsed runners who are intolerant to oral fluid ingestion.

DECEPTION AND PERCEIVED EXERTION DURING HIGH-INTENSITY RUNNING BOUTS '

This investigation examined the overall and localized perceived exertion responses to repeated bouts of submaximal, high-intensity running when subjects were deceived. Well-trained male and female (n = 40) runners were randomly assigned to four groups who completed three 1680-m bouts of running at 80–86% peak treadmill running speed. The two experimental groups, Expected Similar and Expected Increase, were deceived of the actual run intensities while the two control groups, Control Increase and Control Similar, were informed of the actual protocol. After each run, ratings of perceived exertion (RPE) were taken for the whole body, chest, legs, head, and other areas. No significant differences were found in overall RPE between deceived and control groups. However, there was a tendency for the Expected Increase group, deceived into believing the intensity would be higher than they were subsequently made to run, to experience an attenuated increase in RPE between runs compared to the control group (Control Increase) who were honestly informed. For all groups, legs and chest were given consistently higher localized exertion scores than the head and other areas. It appears that a precise system of afferent feedback mediates the overall perceived exertion response during high-intensity running, and psychological intervention that alters pre-exercise expectations has minimal feedforward effect on exertion ratings taken postexercise.

Ethnicity and temperature regulation.

There are at least 31 climatic zones around the world ranging from year-round freezing conditions to daily hot temperatures of around 45 degrees C. Each zone is inhabited by people who have adapted their lifestyles to accommodate the environmental conditions. There are many examples showing physiological and morphological differences between groups living in different environmental conditions (i.e. climate has been shown to influence characteristics including birth weight, body shape and composition, cranial morphology and skin color and sensitivity). Whilst the phenotypic differences are very clear, the genotypic differences are less easy to discern. This can be attributed to the logistical difficulties in executing the definitive study which controls for the environmental and lifestyle factors which themselves induce physiological and morphological changes. However, considering that at least 50 genes have been identified which have altered expression after exposure to heat and at least 20 genes are altered by cold exposure, it is reasonable to assume that more physiological and morphological differences will be attributed to genetic origins as the data becomes available.

Statement of the 3rd International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015

The 3rd International Exercise-Associated Hyponatremia (EAH) Consensus Development Conference convened in Carlsbad, California, in February 2015, with a panel of 17 international experts. The delegates represented four countries and nine medical and scientific subspecialties pertaining to athletic training, exercise physiology, sports medicine, water/sodium metabolism and body fluid homoeostasis. The primary goal of the panel was to review the existing data on EAH and update the 2008 Consensus Statement.1 This document serves to replace the 2nd International EAH Consensus Development Conference Statement and launch an educational campaign designed to address the morbidity and mortality associated with a preventable and treatable fluid imbalance . The following statement is a summary of the data synthesised by the 2015 EAH Consensus Panel and represents an evolution of the most current knowledge on EAH. This document will summarise the most current information on the prevalence, aetiology, diagnosis, treatment and prevention of EAH for medical personnel, athletes, athletic trainers and the greater public. The EAH Consensus Panel strove to clearly articulate what we agreed on, did not agree on and did not know, including minority viewpoints that were supported by clinical experience and experimental data. Further updates will be necessary to: (1) remain current with our understanding and (2) critically assess the effectiveness of our present recommendations. Suggestions for future research and educational strategies to reduce the incidence and prevalence of EAH are provided at the end of the document; areas of controversy that remain in this topic have also been outlined. The 3rd International EAH Consensus Development Conference utilised National Institutes of Health guidelines, amended for a more holistic approach to fit the needs of both the group and the topic. Twenty-two individuals (17 accepted) were invited to participate in the consensus conference who: (1) have made scientific and/or clinical contributions to the topic …

Ice slurry ingestion increases running time in the heat.

OBJECTIVE To examine the effect of drinking an ice slurry (slushy) compared with cold water on prolonged submaximal exercise performed in the heat and on thermoregulatory responses. DESIGN Crossover trial, with the 2 conditions counterbalanced and in random order. Results were adjusted for multiple comparisons by the method of Bonferroni. SETTING Exercise laboratory study; Edith Cowan University, Western Australia. PARTICIPANTS Moderately active male volunteers (n = 10; mean age, 28 years) who participated in recreational sport and who had no injuries or history of heat illness were included. INTERVENTION Five to 14 days before the trials, the participants were familiarized with the procedure by a progressive treadmill run to volitional exhaustion at their previously determined first ventilatory threshold running speed, in the same hot environment as the trials (34°C, 55% relative humidity). The 2 experimental trials were completed at the same time of day, 5 to 20 days apart. During the first 15 minutes, the participants rested while baseline measurements were taken. Over the next 30 minutes, they drank either a 7.5 g/kg flavored ice slurry (-1°C) or the same volume of flavored cold water (4°C) and then commenced the treadmill run. Participants were instructed to keep their normal lifestyle habits stable. In the 24 hours preceding the trials, they were asked to avoid strenuous exercise and to consume a specified amount of carbohydrate and fluid but no alcohol, caffeine, nonsteroidal anti-inflammatory drugs, or nutritional supplements. Urine and blood samples were taken, and respiratory variables, heart rate, and rectal and skin temperatures were continuously monitored. Heat storage was calculated from temperature and anthropomorphic measurements. MAIN OUTCOME MEASURES The primary outcome measures were comparisons of run time to exhaustion, perceived exhaustion, heat storage capacity, and changes in rectal and skin body temperatures during the 2 trials. MAIN RESULTS All 10 participants took longer to fatigue (range, 2.4-14.2 minutes) after ice slurry (mean, 50.2 minutes; SD, 8.5 minutes) than after cold water (mean, 40.7 minutes; SD, 7.2 minutes) ingestion (relative mean increase, 19%; SD, 6%; P = 0.001). Mean rectal temperature during the rest period did not differ between conditions but was 0.32°C lower after drinking the ice slurry than after cold water ingestion before the start of exercise (P = 0.001). During the treadmill runs, rectal temperature rose for both conditions but remained lower for the ice slurry condition for the first 30 minutes of exercise (P = 0.001). After exercise to exhaustion, mean rectal temperature was higher for the ice slurry condition than for the cold water condition (39.36°; SD, 0.41° vs 39.05°; SD, 0.37°; P = 0.001). Mean skin temperature showed a similar pattern to rectal temperature except that the conditions did not differ during or after exercise. During the prerun period, heat storage was lower after ice slurry than after cold water ingestion (-18.28 W/m vs -7.84 W/m; P = 0.001), but during exercise, heat storage was greater after ice slurry than after cold water ingestion (100.10 W/m vs 78.93 W/m; P = 0.005), although the mean rates of heat storage were similar between conditions. During exercise, participant ratings of thermal sensation and perceived exertion were lower after ice slurry than after cold water ingestion, except at exhaustion, when the ratings were similar. CONCLUSIONS Ice slurry (slushy) compared with cold water ingestion prolonged running time to exhaustion in hot and humid conditions, reduced rectal temperature during exercise, and allowed rectal temperature to rise higher before the runner reached exhaustion.