Traditional ideas about drinking during running have lost their steam. The old, dried-up philosophy is that dehydration is to be avoided at all costs and that runners should drink, drink, and then drink some more during their prolonged efforts to avoid overheating and enhance performance. Such desiccated thinking ignores the facts that overheating is caused by environmental conditions and running pace and that the best runners usually end their races more dehydrated than slower individuals.Dehydration

Dehydration: It’s just not what it used to be. In the old days of running, dehydration was a very bad thing, something to be feared. If your sweat losses were great enough during a run, you
automatically became dehydrated, and if you were dehydrated you were suffering from a disease, a pathological condition. Automatically, your risk of overheating – and thus “heat cramps,” “heat exhaustion,” and heat stroke went up, and your performance capacity went down.

Such thinking had a scientific seal of approval, thanks to a classic piece of research carried out by C. H. Wyndham and N. B. Strydom, published in 1969, with the rather ominous title, “The Danger of an Inadequate Water Intake during Marathon Running” (1). This study purported to show that deficient drinking during prolonged running produced dehydration and thus significant health risks. For most runners and coaches, that all seemed logical enough. After all, wouldn’t dehydration reduce plasma volume and thus curtail blood flow to the skin during exercise (a key cooling mechanism)? If an athlete’s body were low on fluid, wouldn’t sweat rates tend to dry up, further impairing the cool-off process?

And– in the dehydrated state - wouldn’t blood flow to the muscles drop, thus decreasing oxygen delivery to the sinews and putting the brakes on running pace? It was hard to answer “no” to those questions, and the solution seemed to be to drink, drink, and then drink some more during
extended running in order to fend off any possibility of desiccation. Today, many runners find themselves securely enmeshed in the dehydration-is-terrible-therefore drink- as-much-as possible during- exercise paradigm. Dehydration

There’s just one problem with all of this: It’s just plain wrong. As Tim Noakes of the University of Cape Town points out, the classic study of Wyndham and Strydom did not really pinpoint any dangers associated with miserly water consumption during marathon running (2). In fact, the
investigation actually revealed that the runners who were dehydrated to the greatest extent were the most-successful – they were the winners of the races which were analyzed!

Nonetheless, the Wyndham-Strydom paper put in place a widely accepted, much-trusted bit
of (il)logic regarding exercise in the heat, namely that (1) dehydration during running causes heat stroke, (2) the only way to prevent heat stroke is to thwart dehydration, and (3) individuals who collapse during exercise in the heat must have a heat disorder related to dehydration, which can only be treated with fluid therapy. Over the past 15 years, Noakes has steadily dismantled this (il)logical structure (although the dismantling has not been adequately noticed by the running community).

First, Tim and his colleagues at the University of Cape Town were able to show that body temperature in marathoners is not related to dehydration status (3). Post-marathon rectal temperatures were taken from 30 fit marathon runners (average VO2max = 58.3 ml.kg 1.min-1) to see if the temps would be related to extent of dehydration, running velocity during the race, and/or estimated, within-race metabolic rates. As it turned out, the marathoners’ body temperatures were significantly linked with their running paces and metabolic rates, not with dehydration. Dehydration

The faster the marathoners ran, the hotter they were. Greater dehydration, though, did not lead to higher internal temperatures. This kind of finding, while somewhat unexpected (given the popularity of the dehydration paradigm), certainly makes sense. After all, about 75 percent of the energy created during running is heat energy – only 25 percent is actually utilized for propulsion.

Faster running means that heat is produced at higher rates, and thus one would expect marathon race pace to be fairly tightly linked with body temperature. Subsequent work by Noakes and co-workers verified the lack of connection between dehydration and overheating – and reinforced the idea that dehydration does not hurt performance. In one study carried out with participants in the 2000 South African Ironman Triathlon, percentage change in body weight during competition (a marker of dehydration) was totally unrelated to post-race rectal temperature or finishing time (4). In a second comprehensive investigation which included athletes from both the 2000 and 2001 South African Ironman competition, body temperature was again not tightly linked with extent of dehydration, and dehydration also failed to predict the risk of medical complications of any kind following the event (5).

Says Noakes, “Humans evolved to run long distances in extreme heat as they chased antelope in
Africa. If they couldn’t do that, they couldn’t survive. Sweating evolved as an adaptation that allowed us to chase the antelope; with sweating, we wouldn’t overheat during the chase. The antelope, in contrast, could not sweat (and still can’t), and thus they overheated, had to slow down, and were captured” (6). Got it? Our ancestors engaged in heavy sweating. It dehydrated them but kept them cool. The poor antelope couldn’t sweat, stayed well-hydrated, and were the losers in this hunting “game.” Dehydration

Dehydration was a good thing, because it helped to prevent overheating. As Noakes points out, the “Bushmen” (San) of southern Africa often wait to begin their hunts until ambient temperature reaches about 40 degrees Centigrade (~ 104 degrees Fahrenheit), knowing that pursuits under such conditions will overheat their prey. In one situation about which Noakes is aware, Bushmen
ran for six hours, while the temperature reached 46 degrees Centigrade (~ 115 degrees Fahrenheit), before overcoming their victims. During those six hours, the San pursuers drank a maximum of one liter of fluid each. They ended up dehydrated – but happy with their success, and without medical complications.

“That is how we evolved the ability to run and the capacity to sweat,” says Noakes. “And sweating– and its associated dehydration – protected us from heat stroke; it did not - and does not - cause it.” “One of the concerns I have is that this condition of dehydration has now become a medical disease. Dehydration actually means that your body fluid stores are reduced. That does not mean that you have a medical condition as a result or that there is an automatic medical crisis caused by fluid loss from the body.

What now frequently happens is that runners, during prolonged exercise, may begin to develop various symptoms, and they often believe that these symptoms are caused by the “disease” called dehydration. Instead of saying, ‘I have a headache,’ a runner tends to immediately make the diagnosis of dehydration because he has been taught that all symptoms during exercise indicate that the medical condition called dehydration must be present. Of course, the runner also believes that there is only one cure – drinking more fluid.” “A key thing for your readers to remember is that dehydration is not a medical condition with specific symptoms and signs like tuberculosis or pneumonia. Dehydration

Rather, dehydration is purely a biological state in which total body water content is reduced. There is absolutely no evidence that - at the levels of dehydration achieved by normal runners – symptoms appear which are the exclusive results of those reductions in body water.” As Noakes points out, runners can actually fare quite well from a performance standpoint while in the dehydrated state. “What they can do in the heat was clearly shown by the winner of the Olympic
Women’s Marathon race in 2004. Mizuki Noguchi, the victor, ran without distress in 35-degree heat (105 degrees Fahrenheit), even though she was drinking very little and thus must have been in a dehydrated condition.”

In fact, as Noakes suggests, moderate levels of dehydration may convey some direct advantages (in addition to the indirect benefits associated with cooling). The moderately dehydrated athlete is lighter than the well-hydrated individual, and thus his/her running economy should be enhanced. In addition, VO2max is expressed per kilogram of body weight, and thus dehydration-related losses in weight might increase VO2max. It is likely that it is no accident that Wyndham and Strydom’s winning marathoners were the most-dehydrated individuals in their overall investigation.

Don’t take all of this the wrong way, though: You’ll still want to consume a sports drink during your exertions lasting an hour or more, especially since the sports drink will provide carbs for your muscles as they gradually become glycogen-depleted during your efforts. The point is that you do not need to over-drink – either before or during your long run or race. Attempting to match your fluid-intake rate with your sweat rate is unnecessary. Rather, a reasonable intake of five to six ounces of sports drink (e. g., five to six regular swallows) every 15 minutes or so during your run is appropriate, even though your sweat rate (and thus body water loss) will probably be greater than that.Dehydration

Note, too, that overdrinking is not only unnecessary: it carries with it a risk of a real medical condition – hyponatremia. Consuming lots of plain water during prolonged running in an effort to ward off dehydration constitutes one of the main risks of developing this sometimes-deadly disorder. As Noakes says, it is far better simply to drink according to the dictates of thirst. “As long as athletes drink according to thirst during their efforts, they will develop neither severe dehydration nor over hydration.” In a recent paper providing guidelines for fluid replacement, Noakes urges athletes not to consume more than 800 ml (~ 27 ounces) of fluid per hour as they exercise (7). ©

References
(1) “The Danger of an Inadequate Water Intake during Marathon Running,” South African Medical Journal, Vol. 43 (29), pp. 893-896, 1969
(2) “Dehydration during Exercise: What Are the Real Dangers?” Clinical Journal of Sports Medicine, Vol. 5 (2), pp. 123-128, 1995
(3) “Metabolic Rate, not Percent Dehydration, Predicts Rectal Temperature in Marathon Runners,” Medicine & Science in Sports & Exercise, Vol. 23 (4), pp. 443-449, 1991
(4) “Weight Changes, Sodium Levels, and Performance in the South African Ironman Triathlon,” Clinical Journal of Sports Medicine, Vol. 12 (6), pp. 391-399, 2002
(5) “Weight Changes, Medical Complications, and Performance during an Ironman Triathlon,” British Journal of Sports Medicine, Vol. 38 (6), pp. 718-724, 2004
(6) Tim Noakes, personal communication
(7) “Fluid Replacement during Marathon Running,” Clinical Journal of Sports Medicine, Vol. 13 (5), pp. 309-318, 2003

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