Considerations in the Use of Body Mass Change to Estimate Change in Hydration Status During a 161-Kilometer Ultramarathon Running Competition
- 507 Downloads
Hydration guidelines found in the scientific and popular literature typically advise that body mass losses beyond 2% should be avoided during exercise. In this work, we demonstrate that these guidelines are not applicable to prolonged exercise of several hours where body mass loss does not reflect an equivalent loss of body water due to the effects of body mass change from substrate use, release of water bound with muscle and liver glycogen, and production of water during substrate metabolism. These effects on the body mass loss required to maintain body water balance are shown for a 161-km mountain ultramarathon running competition participant utilizing published data for the total energy cost, exogenous energy consumption and percentage from each fuel source, average participant body mass, and the extent of soft tissue fluid accumulation during an ultramarathon. We assumed that total energy derived from protein ranges from 5 to 10%, all exogenous energy is used to support the energy cost of the race, glycogen utilization ranges from 300 to 500 g, water linked with glycogen ranges from 1 to 3 g per g of glycogen, and the mass of the bladder and gastrointestinal tract is unchanged from pre-race to post-race body mass measurements. These calculations show that the average participant of 68.8 kg must lose 1.9–5.0% body mass to maintain the water supporting body water balance while also avoiding overhydration. Future hydration guidelines should consider these findings so that the proper hydration message is conveyed to those who participate in prolonged exercise.
This material is the result of work supported with resources and the use of facilities at the VA Northern California Health Care System. The contents reported here do not represent the views of the Department of Veterans Affairs or the United States Government.
Compliance with Ethical Standards
Conflict of interest
Martin D. Hoffman, Eric D. Goulet, and Ronald J. Maughan declare that they have no potential conflicts of interest that are directly relevant to the content of this article.
No funding was received for the conduct of the work or for preparation of the manuscript.
- 19.Nolte HW, Noakes TD, Van Vuuren B. Protection of total body water content and absence of hyperthermia despite 2% body mass loss (‘voluntary dehydration’) in soldiers drinking ad libitum during prolonged exercise in cool environmental conditions. Br J Sports Med. 2011;45:1106–12.CrossRefGoogle Scholar
- 34.McBride JJ, Mason Guest M, Scott EL. The storage of the major liver components; emphasizing the relationship of glycogen to water in the liver and the hydration of glycogen. J Biol Chem. 1941;139:943–52.Google Scholar
- 35.Pukett HL, Wiley FH. The relation of glycogen to water storage in the liver. J Biol Chem. 1932;96:367–71.Google Scholar
- 58.Anonymous. Bushwalker died from drinking too much water. The Sydney Morning Herald. 2012 Sep 17. http://www.smh.com.au/national/bushwalker-died-from-drinking-too-much-water-20120917-2621c.html. Accessed 31 Mar 2017.
- 60.Krabel H. Athlete dies after IM Frankfurt. Slowtwitch.com. 2015. http://www.slowtwitch.com/News/Athlete_dies_after_IM_Frankfurt_5190.html. Accessed 9 Jan 2017.
- 61.HS football player dies from drinking too much fluid. WYFF4.com. 2014. http://www.wyff4.com/news/hs-football-player-dies-from-drinking-too-much-fluid/27409692. Accessed 9 Jan 2017.
- 62.Lilley K. West Point grad dies after hospitalization during Ranger School. Army Times. 2016 Jul 28. http://www.armytimes.com/story/military/2016/07/28/west-point-grad-dies-after-hospitalization-during-ranger-school/87660358/. Accessed 9 Jan 2017.
- 63.Williams A. Jackson Prep football player dies. WAPT News. 2014. http://www.wapt.com/news/central-mississippi/jackson/jackson-prep-prays-for-hospitalized-football-player/27712666. Accessed 9 Jan 2017.