Featured Research

from universities, journals, and other organizations

A Water Tale For All Seasons: When It Comes To Hydration And Exercise, The System Works

Date:
September 5, 2005
Source:
American Physiological Society
Summary:
For 20 years, the US Army Research Institute of Environmental Medicine (USARIEM) has studied the effect of temperature and the environment on physical performance. One recent study showed that dehydration reduced physical performance 8% in temperate/cool air (68F), but only 3% in a cold 36 degrees F. A second USARIEM study found that ingesting glycerol was an effective hyperhydration agent in cold-air exposure. Plus, five "common sense" tips on hydration, exercise and weather.

A second USARIEM-generated study found that ingesting glycerol, asweetish syrup, was an effective hyperhydration agent, causing "nearlytwice as much fluid" to be retained after four hours of cold-airexposure (CAE) compared with water ingestion alone. "This study alsodemonstrates that hyperhydration doesn't modify cardiovascular orthermoregulatory responses during resting CAE," the reported added.

How glycerol may hold water 'in reserve' in body for use later

The implications of the second study are particularly interesting forprolonged outdoor exposure when rehydration is not possible. "Becauseglycerol is freely distributed in body water, hyperhydration with GI(glycerol ingestion) may better preserve the extravascular fluidvolume, accounting for the improved TBW (total body water), comparedwith water alone. This extravascular 'reserve' could later be called onduring exercise or heat stress, when hydration becomes important toperformance and thermoregulation," the paper noted.

Catherine O'Brien, lead author of the glycerol study, said"there's a window of two to six hours where GI could be beneficial.That's a narrow niche where it might be useful for instance forsoldiers on short-range patrol with inadequate access to rehydration."The paper noted that the experiments supported earlier findings"suggesting that glycerol induced hyperhydration through renalreabsorption of water and glycerol. Finally, this study providesinsight into the hormonal mechanisms of cold-induced diuresis and fluidshifts due to hyperhydration."

Next steps

"Whether the degree of hyperhydration" in the current study"is sufficient to improve physical performance in the cold orthermoregulation during subsequent body warming due to exercise or heatexposure remains to be demonstrated," the paper noted.

In addition, O'Brien said: "We learned previously that hydrationdoesn't seem to affect susceptibility to frostbite. But soldiers andoutdoorsmen are more affected by their hands and fingers getting stiff.We're going to look at how physical performance such as manualdexterity can better be maintained in the cold."

Some dehydration shows no performance effect in cold, but does as temperature rises

It's well recognized that athletes perform progressively better as thetemperature falls from hot to cool. It is also known that dehydrationworsens performance in the heat, but its effect in milder environmentsis not well understood. A USARIEM team led by Samuel N. Cheuvront foundthat dehydration by 3% of body weight had little adverse impact oncycling performance in the cold (36F), but markedly reduced performancein temperate air (68F).

"We induced a 3% body weight loss because that's about how much waterthe average marathon runner loses," Cheuvront noted. The team foundthat while this much dehydration produced only a minor negative affectat 36F, at 68F it made a significant 8% cut in performance. "Wemeasured performance as work performed (in kilojoules), but the realindicator is time: 8% over the course of a marathon is the differencebetween finishing in 2 hours 30 minutes or 2 hours 42 minutes -- andthat's a big difference!" Cheuvront said.

He added a quick note of realism, though: "Remember thatalthough we're testing healthy and fit Army recruits, the averagecompetitive runner's performance might not drop as drastically." Theother important finding in the experiment was that with hydration keptsteady, cold in and of itself did not negatively impact performance.

Some elegant measures of "importance" and exertion

Interestingly, the researchers found that during exercise the subjects"thought" they were working at exactly the same rate of exertion, eventhough there was a major difference between their actual performances.

Another measure they used is called the "zone of indifference," whichcan indicate not just whether a finding is or is not "statisticallysignificant, but if it's biologically important or meaningful,"Cheuvront said. "In this case the results were both statisticallysignificant and meaningful," he added. The "spirit of this approach,most closely related to equivalence testing in the clinical sciences,has recently been championed as a performance interpretation tool forthe exercise sciences by Dr. William G. Hopkins," the paper noted.

Next steps: "The preservation of endurance performance in cold air whenhypohydrated may be explained by differences in cardiovascular functionand oxygen uptake dynamics," the paper said. "Although the presentexperiment was not designed to assess the mechanism behind performancechanges, the explanation is reasonable based on the work of others," itadded.

Some 'common-sense' tips on hydration

  • The Boy Scout adage still holds: "Check urine color. It should be relatively clear. If it's dark, you need to drink more," O'Brien said.

  • "Although the 8-by-8 rule of drinking eight 8-ounce glasses of water a day is well recognized, is has almost no scientific basis. The recent Institute of Medicine report on water and electrolytes established an Adequate Intake (AI) for water of 3.7 liters/day for a normal adult male, but there is wide variation. Importantly, that 3.7 liters includes water from food and drink, including beverages like coffee or tea," Cheuvront noted.

  • Exercise fluid intakes should result in neither weight gain nor excessive weight loss (more than 2% of body weight). "Weighing oneself nude before and after exercise is the best way to gauge success around this recommendation," Cheuvront added.

  • Don't drink too much, even in the heat: "We have this mistaken belief that more water is better. Not true. The Army has actually reduced the amount of water it gives in the heat," Sawka said.

  • Even in the cold, other recent USARIEM studies showed that "reduced body water levels (hypohydration) does not increase the risk of hypothermia or peripheral cold injury" such as frostbite, the Cheuvront paper reported.

###

"Tips" Source:
USARIEM and the American Physiological Society

Source: Two USARIEM studies in 'Journal of Applied Physiology'

The two studies from the USARIEM laboratory appear in the Journal ofApplied Physiology, published by the American Physiological Society."Hypohydration impairs endurance exercise performance in temperate butnot cold air," available online, is by Samuel N. Cheuvront, RobertCarter III, John W. Castellani and Michael N. Sawka.

The second paper, "Glycerol hyperhydration: physiological responsesduring cold-air exposure," is by Catherine O'Brien, Beau J. Freund,Andrew J. Young and Michael N. Sawka, and appears in the August issueof JAP.

All researchers for both papers are at the U.S. Army Research Instituteof Environmental Medicine, Thermal and Mountain Medicine Division,Natick, Mass.



Story Source:

The above story is based on materials provided by American Physiological Society. Note: Materials may be edited for content and length.


Cite This Page:

American Physiological Society. "A Water Tale For All Seasons: When It Comes To Hydration And Exercise, The System Works." ScienceDaily. ScienceDaily, 5 September 2005. <www.sciencedaily.com/releases/2005/09/050904225947.htm>.
American Physiological Society. (2005, September 5). A Water Tale For All Seasons: When It Comes To Hydration And Exercise, The System Works. ScienceDaily. Retrieved September 16, 2014 from www.sciencedaily.com/releases/2005/09/050904225947.htm
American Physiological Society. "A Water Tale For All Seasons: When It Comes To Hydration And Exercise, The System Works." ScienceDaily. www.sciencedaily.com/releases/2005/09/050904225947.htm (accessed September 16, 2014).

Share This



More Health & Medicine News

Tuesday, September 16, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

EU Ministers and Experts Meet to Discuss Ebola Reponse

EU Ministers and Experts Meet to Discuss Ebola Reponse

AFP (Sep. 15, 2014) The European Commission met on Monday to coordinate aid that the EU can offer to African countries affected by the Ebola outbreak. Duration: 00:58 Video provided by AFP
Powered by NewsLook.com
Despite The Risks, Antibiotics Still Overprescribed For Kids

Despite The Risks, Antibiotics Still Overprescribed For Kids

Newsy (Sep. 15, 2014) A new study finds children are prescribed antibiotics twice as often as is necessary. Video provided by Newsy
Powered by NewsLook.com
FDA Eyes Skin Shocks Used at Mass. School

FDA Eyes Skin Shocks Used at Mass. School

AP (Sep. 15, 2014) The FDA is considering whether to ban devices used by the Judge Rotenberg Educational Center in Canton, Massachusetts, the only place in the country known to use electrical skin shocks as aversive conditioning for aggressive patients. (Sept. 15) Video provided by AP
Powered by NewsLook.com
Respiratory Virus Spreads To Northeast, Now In 21 States

Respiratory Virus Spreads To Northeast, Now In 21 States

Newsy (Sep. 14, 2014) The respiratory virus Enterovirus D68, which targets children, has spread from the Midwest to 21 states. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins