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.

Effect of exercise, heat stress, and hydration on immune cell number and function.

PURPOSE: The purpose of this study was to determine the effect of thermal stress and hydration status on immune function during exercise. METHODS: Ten trained men completed four cycle ergometer rides at 55% VO2peak under the following conditions: EN (euhydrated neutral; 22 degrees C, 30% RH), DN (dehydrated neutral), EH (euhydrated hot; 38 degrees C, 45% RH), and DH (dehydrated hot). During EN and EH, a carbohydrate/electrolyte beverage was consumed at a rate matching sweat loss, and during DN and DH, no fluid was ingested. Blood samples were drawn pre- and postexercise, and at 2 and 24 h of recovery. Cell counts were determined by automated counting and flow cytometry. Neutrophil activity was assessed as superoxide production, lymphocyte function was determined via PHA-stimulated mitogenesis, and natural killer (NK) cell activity was measured with a 51Cr-release assay. Cortisol was assayed via RIA. RESULTS: Lymphocytes proliferation was depressed 2 h after exercise in all conditions (P < 0.05); however, when expressed on a per cell basis, function was greater in the DH and EH conditions. NK activity (max x 10(3) cells) was greater post compared with preexercise in all conditions (EH = 25.5 +/- 16.8, DH = 26.2 +/- 10.5, EN = 19.3 +/- 11.0, and DN = 16.5 +/- 8.7) but was not different between conditions. Leukocyte, neutrophil, lymphocyte, and NK cell counts were also elevated postexercise with the former two remaining elevated 2 h postexercise in the EH and DH conditions. Cortisol was greater postexercise in EH (22.1 +/- 1.3) and DH (27.7 +/- 1.3) compared with EN (17.8 +/- 2.1) and DN (18.9 +/- 1.6 microg x dL(-1). CONCLUSION: Euhydration did not affect cell number or function when compared with a dehydrated state; however, the hot environment caused more severe disturbances in these measures compared with a neutral environment.

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.

Changes in Running Speeds in a 100 KM Ultra-Marathon Race.

The purpose of this study was to determine if runners who completed a 100 km ultramarathon race in the fastest times changed their running speeds differently compared to those runners who ran an overall slower race. Times were taken from the race results of the 1995 100 km IAU World Challenge in Winschoten, Netherlands. Race times and 10 km split times were analyzed. Runners (n = 67) were divided into groups of ten with the last group consisting of seven runners. The mean running speed for each 10 km segment was calculated using each runner's 10 km split times. Mean running speed was calculated using each runner's race time. The first 10 km split time was normalized to 100, with all subsequent times adjusted accordingly. The mean running speed for each group at each 10 km split was then calculated. The faster runners started at a faster running speed, finished the race within 15 % of their starting speed, and maintained their starting speed for longer (approximately 50 km) before slowing. The slower runners showed a greater percentage decrease in their mean running speed, and were unable to maintain their initial pace for as long. It is concluded that the faster runners: 1) ran with fewer changes in speed, 2) started the race at a faster running speed than the slower runners, and 3) were able to maintain their initial speed for a longer distance before slowing. Key PointsFaster runners in the 100 km race;ran with fewer changes in running speed compared to the slower runners;started the race at a faster running speed than the slower runners;were able to maintain their initial running speed for longer distances than slower runners.

Medical care savings from workplace wellness programs: what is a realistic savings potential?

BACKGROUND: : Workplace wellness programs have become increasingly popular despite large inconsistencies in the analyses of their ability to produce long-term medical care savings. OBJECTIVE: : To clarify the aforesaid situation by estimating potential long-term medical care savings linked to chronic disease. METHODS: : We combined data from the Global Burden of Disease Study and Medical Expenditure Panel Surveys to estimate the annual savings that would result from lowering risk factors typically managed by workplace wellness programs to their theoretical minimums. RESULTS: : Lowering risk factors to their theoretical minimums, if this were possible, would reduce average annual costs per working-age adult by 18.4%. CONCLUSION: : These findings have important implications for workplace wellness programs because they provide a robust estimate of potential savings.

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.

How hot is too hot?: Some considerations regarding temperature and performance.

The regulation of temperature during exercise is a widely debated topic. Two primary views exist, with one embracing a peripheral approach and the other adopting a more integrative and central explanation of the physiology. Especially in the past 10 years, several investigators have published increasingly elegant interpretations that have moved the debate forward.

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.