The NetNutritionist Blog

We all think we need to drink a lot when we exercise, but it can be just as harmful to drink too much as too little. It all depends how much you sweat, says Peta Bee
Germany's Birgit Prinz, right, and her teammates drink water during a break in their soccer semifinals match at the Beijing 2008 Olympics in Shanghai. Photograph: Armando Franca/AP

I have been pedalling hard on a stationary bike for 40 minutes. My thighs are burning and my calf muscles throbbing while sports scientists probe the hi-tech sticking plasters dotted around my body that are designed to assess the quality and quantity of my sweat. Eventually, I am peeled from my saddle to be weighed by Dr Susan Shirreffs, a world-renowned expert in fluid research from Loughborough University's school of sport and exercise science. What might be expected for someone like me - reasonably fit but far from athletic - is that I would be a pound or two lighter than when I started due to the fluid my body expelled during the torturous workout. In hot conditions, it is possible to lose 5lb-8lb in fluid but the scales aren't registering any weight loss in me.

Sweat analysis tests like this are now de rigueur for top athletes. All of Britain's Olympians have undergone a similar assessment prior to Beijing, and footballers from Premiership clubs view them as an essential part of their preparation. According to Shirreffs, the aim of such tests is to determine the rate of fluid lost through sweat so that sports people, and even Joe Joggers like me, can accurately pinpoint the amount they need to drink during exercise to avoid dehydration. "No two people have the same sweat rate," Shirreffs says. "It can vary as much among top athletes as the rest of the population."

My results, which showed that I lost a paltry 315ml an hour of sweat - compared with the 1-2 litres of fluid shed by some people - and a tiny amount of salt (1g in total) suggest I am in the camp that can physiologically cope with drinking very little. Perhaps I was particularly well-hydrated before beginning the trial, it was suggested. But, no, I had run for 30 minutes at lunchtime and drunk only two black coffees and an orange juice before taking up the sweat challenge. Not that the revelations come as a complete surprise.

I have run several times a week since I was 12 and have never needed to carry a water bottle. Only when I have plodded around marathons have I required extra fluid and carbohydrate to keep me going in the later stages.

Periodically my inability to drink and exercise simultaneously (I invariably get a side stitch) has caused me concern because so much emphasis is placed on avoiding dehydration. Yet now there is proof that I never needed much. I wonder how many others are swallowing more than their bodies require? "The majority of people will need up to 500ml of fluid per hour after the first 45 minutes of intense activity," Shirreffs says. "For those who are prone to getting dehydrated, not taking a drink could be disastrous." But, she adds, there is a simple way to tell if you are one of them. Weigh yourself before and after exercise. For every pound you lose, you need to drink around two 10 fl oz glasses (around half a litre) of fluid.

Checking the quality and quantity of your urine can help to tell if you are adequately replacing water loss. Dark and scanty generally suggests it is concentrated with metabolic waste and you need to drink more, although your urine may be darker if you take vitamin supplements (especially vitamin C), so volume is often considered a better indicator.

Staying well-hydrated undoubtedly affects sport performance, and isotonic sports drinks, containing tiny particles of easily-digested carbohydrate that enhance fluid uptake in the gut, are certainly effective. "If the average adult loses 3-4lb of fluid, their performance is seriously impaired," says Louise Sutton, principal lecturer in health and exercise science at Leeds Metropolitan University. "If they lose 7lb, which is possible in the heat, they are likely to get cramps, nausea and experience a 20-30% drop in endurance capacity."

However, in recent years sports scientists have discovered that it is just as risky to drink too much during exercise. Indeed, in many endurance activities, hyponatraemia - or fluid intoxication - is more prevalent than dehydration. Caused by sodium levels and other body salts (or electrolytes) becoming dangerously dilute, hyponatraemia can result in dizziness, vomiting, respiratory problems and fatigue. "During intense or prolonged exercise, the kidneys are unable to excrete fluid as efficiently as normal," Sutton says. "In extreme cases, water is retained, especially in highly absorbent brain cells, and the pressure causes the body to shut down its primary functions, such as breathing and heart rate. Treatment involves a small volume of highly concentrated salt solution. But it can be fatal."

After the 2003 London Marathon, 14 of the runners taken to hospital had hyponatraemia, and a study by Harvard University researchers found that 13% of competitors in the Boston marathon drank enough to cause fluid toxicity. And despite what bottled water and sports drink manufacturers (sports drinks are as likely to cause water toxicity as water) would have us believe, many top athletes drink only small amounts. According to Dr Dan Tunstall-Pedoe, the emeritus medical director of the London marathon, "it's surprising how little elite runners do drink ... they are able to run 26.2 miles at speed with very little fluid on board."

In the British Journal of Sports Medicine, Professor Tim Noakes, from the University of Cape Town and the leading researcher into exercise hyponatraemia, criticised the sports drink industry for positioning their products to the exercising public as "a medicine that must be ingested to prevent heat illness and optimise sports performance. I believe that the body is adapted for conditions of mild dehydration.

"We evolved from hunters - we had to run and chase animals on the hot African plains. We didn't have time to pause for a drink," he says. "Physiologists developed an unproven hypothesis that to become even the slightest bit dehydrated during exercise would kill you. The sports drinks industry then used this bad science to market their products." Runners have died from hyponatraemia, but Noakes says he "has yet to find a death from dehydration in the history of competitive running".

About this articleClose Peta Bee on how much water you actually need to drink while exercising
This article appeared in the Guardian on Tuesday August 19 2008 on p18 of the Comment & features section. It was last updated at 08:23 on August 19 2008.

bodybugg armband bodybugg best price, bodybugg sale, bodybugg special, bodybugg biggest loser
bodybugg 24 hour fitness, bodybugg calorie counter, bodybugg weight loss, bodybugg for life, bodybugg lose weight, bodybugg nutrition, bodybugg success, bodybugg fitness, bodbugg success stories, bodybugg, bodybugg 24 hour , 24 hour fitness bodybugg, bodybugg on TV, bodybugg to you

By MARK SCHOOFS and RON WINSLOW
August 1, 2008

"Exercise in a pill."

That's how researchers are describing two drugs that apparently mimic the effects of physical exercise on the body, raising prospects of new treatments against diseases, new ways to cheat at sports, and new rationalizations for couch potatoes to stuff themselves at brunch.

The Salk Institute
One of the study's tireless mice during its long-distance workout
In a series of startling experiments in mice, the drugs improved the ability of cells to burn fat and retain muscle mass, and they substantially prolonged endurance during exercise. Using one of the compounds for just a month, even sedentary, couch-potato mice improved their endurance running by a staggering 44%. Some mice that combined a month of exercise with the other drug bolstered their long-distance running by about 70% over untreated mice.

One of the drugs is already in late-stage human trials for other purposes, and the mouse experiments raise hopes for new strategies to protect people against obesity, diabetes and muscle-wasting diseases such as muscular dystrophy.

But underscoring the risks, one of the compounds has been withdrawn from human trials because of toxic side effects, and researchers said that the drugs could easily be abused by competitive athletes to enhance their performance. Researchers have already devised a test to detect them in blood and urine.

A spokesman for the World Anti-Doping Agency said in a written statement that, following policy, it wouldn't say when the test would go into use. But the statement noted that "a number of anti-doping organizations, including the International Olympic Committee, store doping control samples of their events for eight years for potential future retesting." A spokeswoman at GlaxoSmithKline, which developed one of the drugs, said that if athletes get their hands on the drug, "they won't be getting it from us."

The exercise-pill study, published Friday in the journal Cell, was conducted on mice, and it is possible that the drugs may show less benefit, or even none at all, when applied to humans. Still, the underlying genetic switches activated by the drugs appear to be the same in humans and mice.

ENHANCED ENDURANCE

• See video of two mice, one that received one of the drugs tested and another that didn't, exercising on treadmills.
• Health Blog: Experimental Drug Boosts Endurance... in MiceThe researchers examined how the drugs acted on the cellular and molecular level, but they also evaluated the simple ability of mice to run on a treadmill. Unlike humans who may suffer a motivational issue before exercise, "mice are very good at running as far as they can," said principal investigator Ronald Evans, a researcher at the Salk Institute for Biological Sciences, La Jolla, Calif., and the Howard Hughes Medical Institute. "When they get exhausted they just stop running. They can't run any more."

First, Dr. Evans and his team gave the mice a drug known as GW1516, which used to be under development by GlaxoSmithKline as a drug against dyslipidemia, a disorder affecting cholesterol. Side effects forced the company to scuttle it, a Glaxo representative said.

Still, the drug enabled mice to run for more than three hours, compared with less than two hours for untreated control mice. But this drug's effect occurred only when the mice also got regular exercise; sedentary mice got no benefit from the drug. "This is the no-pain, no-gain drug," said Dr. Evans.

Based on research into the genetic switches that control endurance muscle cells, Dr. Evans and his team decided to give the mice a second drug: AICAR, or acadesine, which was recently licensed by Schering-Plough Corp. and is in late-stage trials for the prevention of problems that can occur during coronary surgery. This drug enabled even sedentary mice to run longer, as if they were in good physical condition. "That is the true couch-potato experiment," Dr. Evans said.

Anabolic steroids, often abused by athletes, enhance the performance of fast-twitch muscle cells -- those that provide power and speed. The two drugs being researched are among the first compounds shown clearly to improve the slow-twitch muscle cells used in endurance activities. Whereas fast-twitch muscle cells burn sugar, slow-twitch cells primarily burn fat, which means they could help combat obesity. Previously, resveratrol, found in red wine, was shown to enable mice to run farther, but exactly how it works on slow-twitch muscles isn't clear. A person would also have to drink "hundreds of bottles" of wine to get enough resveratrol to improve athletic performance, said Dr. Evans.

Patients who are bedridden or wheelchair-bound "can't exercise, and this would give them some of the benefits," said Joseph Hornyak, associate professor of physical medicine and rehabilitation at the University of Michigan at Ann Arbor. But the pills would be unlikely to provide all the benefits of real exercise. "People who exercise have lower levels of depression and higher bone density," said Prof. Hornyak. "Whether or not this pill would confer those benefits, we don't know."

The broadest appeal of the drugs may be for gain-without-pain preeners who would sooner pop a pill than strain themselves or a hamstring. Such "off-label" use is "not only a real possibility but a probability," said Dr. Evans.

If the medicine "results in better-looking people, that would be good," said comedian Fran Lebowitz. "All I have right now is a vision of slim, vain, lazy mice."

bodybugg armband bodybugg best price, bodybugg sale, bodybugg special, bodybugg biggest loser
bodybugg 24 hour fitness, bodybugg calorie counter, bodybugg weight loss, bodybugg for life, bodybugg lose weight, bodybugg nutrition, bodybugg success, bodybugg fitness, bodbugg success stories, bodybugg, bodybugg 24 hour , 24 hour fitness bodybugg, bodybugg on TV, bodybugg to you