The Evolving Science of Hydration

On a hot and humid summer day of 1904, thirty-two runners started a 24.85-mile course in St. Louis where water was provided at just two stations. The current thinking was that drinking during exercise was unnecessary. In fact, to compete without nourishment was a worthy achievement.

The high metabolic heat produced during exercise causes our core temperature to rise to dangerous levels (normal core or internal temperature is 98-100 degrees). The body’s counter measure is to increase the heart rate so that blood flow is maintained to the exercising muscles and the skin to allow for the dissipation of heat through sweating. When sweating becomes the primary means of heat dissipation, however, sweat loss must be matched by fluid consumption to avoid dehydration.

By 1923, the topic of exercise physiology was advanced by studies that emphasized the risks of dehydration during exercise. This research was the primary impetus for the “cardiovascular” model of physiology and thermoregulation, which predicts that there is a point at which increases in heart rate can no longer compensate, leading to reduced blood flow to the skin, an increase of core temperature, risk of heat stroke, or myocardial infarction (heart attack).

For decades, substantial research into hydration and performance supported the position that exercise performance is impaired when a level of dehydration due to sweating reaches about 2% body mass loss. The 1996 position stand of the American College of Sports Medicine (ACSM) stated, “Even a small amount of dehydration (1% body weight) can increase cardiovascular strain as indicated by a disproportionate elevation of heart rate during exercise, and limit the ability of the body to transfer heat from contracting muscles to the skin surface where heat can be dissipated to the environment.”

But these recommendations famously ignored evidence that some of the fastest marathon runners had incurred a water deficit exceeding 4%. Using data from a review of these marathon runners, when the relationship between running speed and percentage dehydration was plotted, the best-performing runner was dehydrated by some 8%, while the only runner to prevent body mass loss of >2% was the slowest (Fig. 1). The data suggests the effect of dehydration in excess of 2% did not impair performance significantly.

Figure 1: American College of Sports Medicine

By 2007 ACSM’s revised consensus statement regarding fluid consumption during exercise reflected the new thinking that preventing all dehydration may be unnecessary, and that there may exist a level of “tolerable dehydration“.

It’s important that athletes maintain adequate hydration levels before and after training as well. Any fluid that doesn’t contain alcohol can hydrate. Food counts too!

New research has suggested that it is whole-body hyperthermia (defined as core body temperature exceeding 40°C; 104°F) that impairs performance rather than dehydration levels per se. In one study (Trangmar SJ, Chiesa ST, Kalsi KK, et al.), participants were placed under sufficient heat stress to either raise skin temperature or to raise skin temperature and core temperature. The participants with elevated skin temperature did not experience impaired exercise performance, whereas participants with an increase in whole body temperature did. This suggests a high sweat rate prevents a rise in core temperature (hyperthermia) even though it also results in a water deficit (dehydration). The higher sweat rate allowed the faster athletes to run faster than the slower runners because they were able to dissipate more core heat through sweating. We began to see that the best hydration strategy could only be determined by the athlete’s individual requirements rather than a one-size-fits-all recommendation.

The latest position (2016) of the ACSM: ”Dehydration/hypohydration can increase the perception of effort and impair exercise performance; thus, appropriate fluid intake before, during, and after exercise is important for health and optimal performance. The goal of drinking during exercise is to address sweat losses which occur to assist thermoregulation. Individualized fluid plans should be developed to use the opportunities to drink during a workout or competitive event to replace as much of the sweat loss as is practical; neither drinking in excess of sweat rate nor allowing dehydration to reach problematic levels.”

Hydration theories have taken many turns. For example, we now know that a mixture of glucose, maltodextrin, fructose, sucrose and galactose – in other words, carbohydrates (also written as CHO), improves endurance performance by maintaining blood glucose and muscle glycogen stores, resulting in a levelling-off in core temperature. And so it was, with a mixture of sugar, salts and lemonade, the first sports drink was born.

Lucozade – basically citrus flavored sugar water – launched in 1927 and was the earliest traceable ancestor of the sport drink. Owned by the Beecham Company, they merged with SmithKline many years later. Gatorade launched its first product in 1967.
Photo Courtesy: Precision Hydration where you can get more info on sports drinks and take a free online sweat test.

The problem with these early sports drinks and gels is that our stomachs don’t always do well with high concentrations of sugar. Frequent GI distress prevailed over the next few decades of running.

A more recent innovation for providing fluid and CHO during exercise is the use of alginate. Alginate is a naturally occurring anionic polymer typically derived from seaweed and commonly used in oral drug delivery, wound healing, and tissue engineering.

Maurten is one such company delivering gels that are a combination of Alginate (extracted from the cell walls of brown algae) and Pectin (found in apples, lemons, carrots, tomatoes, etc.). When mixed with water, the resulting ‘sports drink’ converts to hydrogel in the acidity of the stomach, encapsulating the carbohydrates. Athletes that experience gastric (GI) distress from sugary sports drinks will appreciate that there were no reports of GI distress with any drink including the alginate hydrogel. And because it is engineered to encapsulate the carbs with the process beginning only when contact is made in the stomach, it is also better in terms of dental health.

Dental health is an important issue with CHO-based sports drinks. A survey at the London 2012 Olympic Games found that 18% of athletes reported that their oral health had a negative impact on their performance and 46.5% had not been to a dentist in the past year. (The latest ACSM position statement also addresses oral health in the wider culture of sports health care and health promotion.)

The next evolution in hydration began in 2014 when the Brazilian National Football Team asked Gatorade to help them prepare for the World Cup. The team didn’t end up winning the World Cup, but the pilot opened new doors for collaboration and innovation at Gatorade.

Smart Design worked with the Gatorade Sports Science Institute (GSSI) to research heat stress and dehydration during exercise. A systemized approach was developed to test and analyze how each athlete sweats—how fast, how much and in what concentration. The resulting product was a hydration platform – a bottle with a “smart cap” that’s built on the hypothesis that personalization is the next frontier of improving athletic performance.

The new Gatorade squeeze bottle utilizes Drinkfinity beverage pods, allowing quick delivery of sport-specific or individualized player formulas. Courtesy: PepsiCo
Courtesy Gatorade

Today’s consensus is that drinking to thirst is the body’s best hydration strategy, and in most cases will protect athletes from the hazards of over and under drinking by providing real-time feedback. It’s important to research and practice various hydration approaches during training runs to understand your specific needs, and to develop a personal strategy. Some athletes are less aware of their hydration requirements and may benefit from technology, such as a fluid calculator. But the quantity, amount, or combinations of food and/or fluid consumed while exercising should always be guided by your individual palatability and tolerance.

There is still a widespread misconception that you should ‘stay ahead’ of your thirst. Drink early and often was the advice we were given years ago; advice too many runners still follow.

Slower runners generally sweat less, but have been told to drink copiously. If you ingest more fluid than you lose through sweating or urination, however, you dilute your blood’s sodium levels – a condition called hyponatremia, or water intoxication, caused by drinking too much. Osmosis then draws water from the blood into body cells to equalize sodium levels, and those cells swell. If the cellular bloating occurs in the brain, it can be fatal.

The latest position statement from the International Marathon Medical Directors Association (2006) included a Final Word:

“There are no shortcuts toward great achievement, and marathon running is no exception. Clinicians and scientists must resist handing out unrealistic ‘‘blanket advice’’ to individuals seeking simple answers, but rather should encourage athletes to explore, understand and be flexible toward their own needs. By providing guidelines and advice on how to appropriately understand individual fluid replacement needs, we can eliminate future fluid balance problems by avoiding the temptation to generalize one rule for every situation and every athlete.”

My husband believes this more individualized protocol of hydration will serve to open up the sport to runners that may have otherwise found it too uncomfortable or difficult to participate. That in some way, having technology that explains how to hydrate will win them over to the sport. Maybe it’s even a marketing ploy on behalf of the corporations involved. I’m not sure I disagree.

To a seasoned runner, technological advancements may seem unnecessary. To a new runner, they may provide much needed guidance in a world of overwhelming challenges. It may or may not make you a better runner. Some would say technology is most useful at the far ends of the spectrum – in this case, for new runners and elite runners.

Many years ago I wore a special shoe with a piece of plastic in the bottom that could tell me how far I’d gone and at what pace. Some of you may have worn those same shoes. I suppose it helped me learn to pace myself better, but mostly it was new and fun.

When I ran in Kenya, a group of runners were heading out on a 40k training run. Knowing water was not easy to come by, I asked the runner I was with how often they would drink. He smiled and told me, “When they’re finished.” I used to never drink on a training run of any length. But there also came a time that I hid extra water bottles on my route and ate a peanut butter sandwich along the way. My main hydration strategy for race day was to try to avoid having to stop at the port-a-potty.

These new guidelines, and even more recent studies, emphasize that we are all unique and our hydration strategies will be equally unique. This left my husband feeling empty. He wanted something more absolute. I told him that now there’s an app for that.

 

Additional Reading:

The Best Hydration Plan Is to Drink When You’re Thirsty, Sweat Science at OutsideOnline.com 

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