Weight Change and Hydration Status During a 161-km Ultramarathon

Abstract

s From the Second Annual Medicine & Science in Ultra-Endurance Sports Conference, June 2015, Olympic Valley, CA The Influence of Hydration on Thermoregulation During a 161-km Ultramarathon Taylor R. Valentino, MS; Kristin J. Stuempfle, PhD; Marialice Kern, PhD; Martin D. Hoffman, MD San Francisco State University, Gettysburg College, Univeristy of California Davis Medical Center and Sacramento VA Medical Center Objective.—It is commonly advised that individuals should avoid losing 42% of their body weight during exercise because dehydration can ultimately lead to hyperthermia, which will impair performance. However, body weight losses of Z3% appear to be well tolerated in those participating in prolonged endurance exercise. This study sought to determine the relationship between hydration status and thermoregulation of runners participating in a hot ultramarathon and to assess whether a weight loss of42% body weight leads to elevations in core temperature. Methods.—Thirty runners of the 2014 161-km Western States Endurance Run agreed to take part in the study. Body weight and core temperature were measured at the start, at 3 locations during the race, and at the finish. Results.—Of the 30 starting participants, 20 finished the race. Ambient temperature at data collection sites ranged from 171C to 391C, and the highest core temperature recorded was 39.41C. Core temperature did not significantly differ during the race (P 1⁄4 .77) and was not correlated with body weight change (P 1⁄4 .19) or finish time (P 1⁄4 .11). However, body weight change was directly associated with finish time (r 1⁄4 .60, P 1⁄4 .006), such that the fastest runners had the greatest loss in body weight ( 3.5–4.0%). Neither core temperature nor percent body weight change differed between race finishers and non-finishers (P 1⁄4 .63 and .17, respectively). Conclusions.—While participating in endurance exercise up to 30 hours in hot conditions, runners can tolerate weight losses of 43% body weight without significant rises in core temperature. Therefore, since body weight losses of 43% were not associated with a rise in core temperature, an emphasis on fluid replacement for weight losses of this magnitude during prolonged exercise is not justified as a preventative measure for heat-related illnesses. Supported by the Western States Endurance Run Foundation. Weight Change and Hydration Status During a 161-km Ultramarathon Karin D. VanBaak, MD; Jack Spittler, MD; Bjorn Irion, MD; Martin D. Hoffman, MD; Morteza Khodaee, MD, MPH University of Colorado, Denver CO, Texas AM Theodore L. Bross, BS; Martin D. Hoffman, MD Palm Beach Atlantic University, Boonshoft School of Medicine, Wright State University, University of California Davis Medical Center and Sacramento VA Medical Center Objective.—To assess the quality of information currently available to the public about hydration needs during exercise. Methods.—Internet searches were conducted using the terms “hydration,” “hydration guidelines,” “drinking fluids,” and “drinking guidelines” with “and exercise.” From the first 50 websites for each search phrase, duplicates were removed, yielding 145 unique websites. Websites were then categorized and examined for specific information and recommendations. Results.—Overall correct endorsement of current knowledge was as follows (reported as percent endorsing the concept relative to the number of sites addressing the issue): some weight loss should be expected during exercise (67.6% of 102), fluid consumption during exercise should be based on thirst (9.4% of 106), electrolyte intake is not necessary during exercise (12.5% of 112), dehydration is not generally a cause of heat illness (6.9% of 58) or muscle cramping (2.3% of 43), exerciseassociated muscle cramping is not generally related to electrolyte loss (6.7% of 15), and overhydration is a risk for hyponatremia (98.5% of 65). There were 7.1% (of 70 websites addressing the issue) indicating that any weight loss during exercise should be avoided. Comparison of website information from those in the categories of medical or scientific organization (15.9%), academic institution (9.0%), peer-reviewed publication (8.3%), and medical professional individual or facility (8.3%) with those in the categories of media (19.3%), sports organization or coach (9.7%), sports drink or electrolyte replacement manufacturer (3.4%), and other (26.2%) revealed no differences (P 1⁄4 .38 to 1.0) in the frequency of endorsement of the criteria referred to above. Conclusions.—Misinformation about hydration needs during exercise continues to be widely spread on the Internet. In general, those websites that should be most trusted by the public appear to be no better than other websites at providing accurate information, and the potential risk of hyponatremia is not often raised.