Wednesday, September 24, 2008

Hydration and Exercise, Part 3

Those cloistered within the ivy-covered walls of university human-performance labs aren’t always very good about giving us real-world answers to real-world questions. From their research we can often get suggestions, possibilities, and general directions. But they seldom go out on a limb and tell the athlete what to do in given situations. Straight answers to clear questions are rare in academia. That is left for those in the field – the athletes and their coaches – to figure out for themselves.

It seems that the more you know about something, the more possibilities you can see for how the question might be answered. I suffer from this affliction, also. With every passing year of studying sport science I find my answers to athletes’ questions are more likely to start with “it depends.” I try not to, but as soon as I say do such-and-such, someone is going to say, “Well, that doesn’t help in this unique situation.” So I hedge my bets knowing that there are just too many variables in studying humans to give sure-bet answers to even the simplest of questions.

I’m telling you this because I am about to answer some simple questions about hydration and exercise, or at least they appear simple on the surface. I’ll try hard not to say “it depends.” But no promises. Sometimes I just can’t help myself. The answers are some mix of what I’ve seen in research and my experiences as an athlete, coach and observer of sport. Here goes…

Q: How much should I drink during a race or workout?
A: This gets back to Part 2 of this series. You should drink enough to satisfy your thirst. I know this seems simplistic and athletes often being type A want something more complex and defined. How could anything so simple actually work? But how much you drink depends (oops) on the conditions of the race or workout and how much you are sweating. The bottom line is that you’ll need less fluid in cool weather than hot. How hot is hot and how cool is cool? (I just can’t control myself!) How much fluid you need also varies based on how hard you are working. Rather trying to come up with tables that you study before exercise with various situations there is a rather simple solution: drink when you are thirsty and drink until satisfied. If you do that there is no need to give it any deeper consideration. Thirst is a great mechanism and is quite accurate despite what we’re told. The challenge, of course, is paying attention to it. If you become singularly focused on other matters, such as your competition or pacing, then you are likely to forget to pay attention to your signs of thirst such as a dry mouth. During a workout or race you should be repeatedly running through a checklist in your head of many items including thirst.

Q: Should I drink enough during exercise to maintain my body weight?
A: No, you should not (how’s that for being definitive?). You will lose weight during exercise primarily due to dehydration and secondarily to the consumption of energy stores. The latter is quite small as a portion of your body weight. Trying to maintain body weight by drinking large amounts of fluid sets you up for hyponatremia as described in Part 2 of this series (below). Well before your sodium stores become significantly diluted you may well experience what Ironman triathletes call “stomach shutdown” with what I suspect is the gut's inability to process fluid or food due to having taken in too much water or sports drink. This may be accompanied by nausea which is good because vomiting would remove excess fluid in the stomach.

Q: How much weight loss due to dehydration is acceptable and can be well-tolerated by the body?
A: The standard answer used to be 2% but that keeps going up in the literature with most finding that a 3% loss of body weight due to dehydration has no significant effect on endurance performance [1,2,3]. But one recent study did find an 8% decline in cycling time trial performance with a 3% loss of body weight due to dehydration in a moderate temperature of 68F (20C) but not at 36F (2C) [4]. Around 4-5% losses do seem to have negative consequences, however [5]. For a 154-pound (70kg) athlete 4% of body weight is just over 6 pounds (2.8kg). Assuming that a pint of water weighs about a pound, this would be a loss of 3 quarts (nearly 3L) of fluid. That would be a gross error in hydration and would certainly indicate that the athlete was not paying attention to thirst. The bottom line is that you should lose water and therefore body weight during exercise, but if you drink until satisfied when thirsty then body weight losses and therefore dehydration will not be an issue. That’s “managed dehydration,” to again use coach Gordo Byrn’s apt phrase.

Q: How do I gauge my level of dehydration following exercise and then go about replacing lost fluid?
A: This one is easy and by now you should also know the answer: Drink according to your thirst. If thirsty, drink. When no longer thirsty, don’t drink. It’s pretty simple. There is no reason for elaborate drinking schedules or water volume goals. I recently read an article by a noted nutritionist who suggested that Ironman triathletes should drink 180 ounces (5400ml) of water daily. Wow! That’s really not necessary or even healthy. Thirst does indeed work. And also be aware that fluid comes not just from drinking but also from the food you eat. For example, a study of 14 elite Kenyan runners whose water losses and rehydration were tracked for 5 days supports this notion [6]. No instruction was given on how much to drink. During workouts they drank nothing and typically lost 2.7% of body weight daily. On average they took in 4 quarts (3.8L) of fluids daily based entirely on thirst. No changes were reported in daily hydration status, body weights or responses to training over the course of 5 days.

Let’s stop now and allow you to think about all of this. I’ll be away from the office the rest of the week. Next week I’ll answer more questions along this same line and get into the matter of how to replace fuel expended during exercise, also.

1. Cheuvront, S.N., R.I. Carter, M.N. Sawka. “Fluid Balance and Endurance Exercise Performance.” Current Sports Medicine Report 2 (2003): 202-208.
2. Oliver, S.J., S.J. Laing, S. Wilson, J.L. Bilzon, N. Walsh. “Endurance Running Performance After 48h of Restricted Fluid and/or Energy Intake.” Medicince and Science in Sports and Exercise 39, No. 2 (2007): 316-322.
3. Laursen, P.B., R. Suriano, M.J. Quod, H. Lee, C.R. Abbis, K. Nosaka, D.T. Martin, D. Bishop. “Core Temperature and Hydration Status During an Ironman Triathlon.” British Journal of Sports Medicine 40, No. 4 (2006): 320-325.
4. Cheuvront, S.N., R.I. Carter, J.W. Castellani, M.N. Sawka. “Hypohydration Impairs Endurance Exercise Performance in Temperate but not Cold Air. Journal of Applied Physiology 99, No. 5 (2005): 1972-1976.
5. Slater, G.J., A.J. Rice, K. Sharpe, R. Tanner, D. Jenkins, C.J. Gore, A.G. Hahn. “Impact of Acute Weight Loss and/or Thermal Stress on Rowing Ergometer Performance.” Medicince and Science in Sports and Exercise 37, No. 8 (2005): 1387-1394.
6. Fudge, B.W., C. Easton, D. Kingsmore, F.K. Kiplamai, V.O. Onywera, K.R. Westerterp, B. Kayser, T.D. Noakes, Y.P. Pitsiladis. “Elite Kenyan Endurance Runners Are Hydrated Day-to-Day with Ad Libitum Fluid Intake.” Medicince and Science in Sports and Exercise 40 (2008): 1171-1179.

Sunday, September 21, 2008

Hydration and Exercise, Part 2

First off I want to apologize to you for the big gap since my last post. A week ago our home was burglarized and among all of the stuff stolen were our computers. That put me out of business for a few days. But I’m back up to speed now so let’s get back to the topic of hydration, or as coach Gordo Byrn calls it, “managed dehydration.”

I think coach Byrn’s two-word summary is an appropriate mindset as you read what I’ve got to say here and in Part 3. I suspect you may not agree with all of this. I would certainly understand as I also resisted the evidence I had seen over the past several years in favor of what I had been told by so many experts including scientists. This post may turn your world upside down, but bear with me as we work through this. Change is never easy.

Over the last few weeks I’ve been rethinking what I understand and believe about hydration during exercise. In a single sentence, here is what I’ve come to believe endurance athletes should do during exercise in regards to hydration: Drink when thirsty; don’t drink when not thirsty. For shorter endurance events – those lasting less than, let’s say, four hours – that’s a not a huge change. And the shorter the event the more likely the athlete is to drink to thirst any way.

But that suggestion flies in the face of what I’ve suggested to the athletes I’ve coached in long endurance events such as Ironman triathlons and marathons. For at least 20 years I’ve told them they needed to have a hydration schedule during such events and stick with it, even setting their watch to beep every 10 minutes or so to remind them to drink. This was based on the oft-repeated axiom that when you become thirsty it’s too late. The research does not generally support this notion [1,2] with the possible exception of older athletes [3,4,5] although not all of the research agrees on this age issue [6]. Generally, when left to their own devices, a thirsty athlete will drink sufficiently to maintain an adequate level of hydration without negative consequences for performance. The key is paying attention to your thirst.

I’ve also said that for long events completed in the neighborhood of about 12 hours or less that their hydration source should also be their refueling source. Basically, that means they needed to use a sports drink for both water and calories. As the finishing time gets longer than 12 hours I’ve suggested they use more solid foods and wash them down with water and sports drinks. And, I said, nearly all long-endurance athletes should be supplementing with sodium even though their sports drinks probably already have some in it.

Now I’ve changed my mind on all of this. It hasn’t been easy. I’ll try to explain.

There is one bit of information I had been unable to account for given my former position on hydration. It had been staring me in the face but I’d ignored it. This has to do with the body’s sodium concentration. During exercise, as fluid is lost through sweating and in other ways, the concentration of sodium in the body actually increases. The reason is because much more fluid is lost than sodium. One might lose around a liter of water during exercise but only lose a small amount of sodium in sweat. Normal body sodium levels are about 140 millimoles per liter (mmol/l) of water while sweat is about 20 to 60mmol/l.

So let’s say an average-sized human body contains 40 liters of water when at rest and normally hydrated. That means it has stored away something like 5600mmol of sodium (40 x 140 = 5600). If one liter of fluid is lost during exercise and with that 60mm of sodium are excreted (the high end, or “salty” sweater) then the new sodium concentration is about 142mmol/l (5600 – 60 = 5540 / 39 = 142.05). The concentration of sodium has risen, not declined. Guess what happens next after a sufficiently large rise in sodium concentration occurs – your thirst mechanism kicks in and you drink water to dilute the sodium bringing it back down to something closer to 140mmol/l. One study found that a rise of about 2-3% of plasma sodium concentration evoked a strong desire to drink [7].

So your sodium becomes more concentrated during exercise as you sweat, not less as we’ve been led to believe. In other words, you don’t need to replace lost sodium during exercise because the loss is inconsequential while the volume of water lost is significant. But even if you did, the sodium content of most sports drinks is 10-25mmol/l, not enough to replace the loss (unless you overhydrate which raises the specter of hyponatremia - more on that shortly). More than about 25mmol/L of sodium makes the drink unpalatable. The extracellular fluid in your body, where much of the sodium is stored, is about the concentration of sea water. If you’ve ever swallowed sea water you know how bad that would be to drink. So should you therefore supplement with sodium capsules during an ultra event? I’ll get at that in Part 3.

Would not taking in sodium during a long race or workout impact your performance? Not according to the research. Adding sodium to a sports drink did not improve performance in a time trial effort after four hours of exercise at a moderate intensity [8]. Nor did sodium in a sports drink impact the ability to complete six hours of moderate-intensity exercise [9].

The greater issue for the long-endurance athlete is hyponatremia. This was discussed in Part 1 of this series (see Hydration, Part 1). The condition of hyponatremia is considered to be a sodium concentration level of less than 128mmol/l by some. As you can see from the example above the only way to get there would be to drink more water than is lost during exercise. That would dilute your sodium stores. So the issue is not replacing sodium but rather not drinking too much fluid. Thirst is the key to this balance. If you drink only when thirsty and to a level which satisfies thirst then you will not drink too much.

I know I haven’t yet answered the questions at the end of Part 1 in this series on hydration, but I’m going to stop here and let this sink in. In Part 3 I’ll get at how I now deal with those questions for the athletes I coach.

1. Maresh, C.M., et al. “Effect of Hydration Status on Thirst, Drinking, and Related Hormonal Responses During Low-Intensity Exercise in the Heat.” Journal of Applied Physiology 97, No. 1 (2004): 39-44.
2. Schroeder, J.M., et al. “A Comparison of Three Fluid Replacement Strategies for Maintaining Euhydration During Prolonged Exercise.” Canadian Journal of Applied Physiology 22, No. 1 (1997): 48-57.
3. Leaf, A. “Dehydration in Elderly.” New England Journal of Medicine 311 (1984): 791-792.
4. Marszalek, A. “Thirst and Work Capacity of Older People in a Hot Environment.” International Journal of Occupational Safety and Ergonomics No. 135 (2000): 135-142.
5. Ainslie, P.N., et al. “Energy Balance, Metabolism, Hydration, and Performance During Strenuous Hill Walking: The Effect of Age.” Journal of Applied Physiology 93, No. 2 (2002): 714-723.
6. Bossingham, M.J., et al. “Water Balance, Hydration Status, and Fat-Free Mass Hydration in Younger and Older Adults.” American Journal of Clinical Nutrition 81, No. 6 (2005): 1342-1350.
7. Hubbard, R.W., et al. “Influence of Thirst and Fluid Palatability on Fluid Ingestion.” In Gisolfi, C.V., D.R. Lamb, eds. “Perspectives in Exercise Science and Sports Medicine.” Vol. 3. Fluid Homeostasis During Exercise. Indianapolis, IN: Benchmark Press (1990): T96.
8. Merson, S.J., et al. “Rehydration with Drinks Differing in Sodium Concentration and Recovery from Moderate Exercise-Induced Hypohydration in Man.” European Journal of Physiology 103, No. 5 (2008): 585-594.
9. Barr, S.I., et al. “Fluid Replacement During Prolonged Exercise: Effects of Water, Saline, or No Fluid.” Medicine and Science in Sports and Exercise 23 (1991): 811-817.

Friday, September 5, 2008

Hydration and Exercise, Part 1

Until recently relatively small losses of body weight due to dehydration during exercise were thought to be detrimental to athletic performance. The threshold for drops in performance related to dehydration has long been considered to be around 2% of body weight [1]. So a 150-pound man who lost 3 pounds or a 125-pound woman who dropped 2.5 pounds during exercise were expected to slow down as a result. In 1996 the American College of Sports Medicine (ACSM) went a step further suggesting that the loss of any body weight due to dehydration could potentially result in poor performance or even health issues [2]. Their position stand was that an athlete should drink enough to replace all water lost through sweating and that this would likely be in the range of 18 to 36 ounces (600-1200mL) of fluid per hour. Last year the ACSM officially changed their stand by adopting the more common 2% of body weight as the upper end of what an athlete should lose due to dehydration [3]. This time they stopped short of making recommendations on how much to consume.

Two-percent is still too low according to Tim Noakes, PhD, a South African exercise physiologist who has led the fight to get the ACSM and other sports organizations to relax their standards on drinking during exercise [4]. Why would Noakes want us to drink less during racing and training? The reason is something called “hyponatremia” – the dilution of the body’s stores of sodium. Athletes who were encouraged to replace all fluids lost while exercising as per the 1996 ACSM position stand put themselves at risk for this condition which is worse than the dehydration they were trying to prevent, according to Noakes [5]. And he believes that 2% still encourages excessive drinking and encourages risk.

By over-hydrating while exercising, sodium concentrations drop and put you at risk for hyponatremia. Some early signs of hyponatremia are bloating around elastic bands in socks and the waistbands of shorts, disorientation, headache, nausea, muscle cramps, lethargy, confusion, reduced coordination and tunnel vision. In recent years there have been deaths in back-of-the-pack runners related to hyponatremia. Drinking an excessive amount of water for several hours during exercise (4 hours is considered the danger threshold) increases your risk. One study of Ironman-distance triathletes going way back to 1987 found that as few as 8% and as many as 30% of the race finishers experienced mild to severe hyponatremia [6].

It’s generally accepted that elite athletes have a lower risk of hyponatremia but a higher risk of dehydration since they are focused on performance and may take in less fluid than demanded by the body. Slower athletes simply have more time to drink and may well believe it is in their best interests to consume a lot of water. The mistaken notion that we should finish a workout or race with no loss of body weight further increases the risk, especially in long events.

So what does all of this mean for your training and racing? How much should you drink during a race or workout? What should you drink? How much weight loss due to dehydration is acceptable and can be well-tolerated by the body? Should you drink extra amounts in the days and hours leading up to a race in hot conditions so that you’re hyperhydrated? How do you gauge your level of dehydration following exercise and then go about replacing lost fluid? Does age have any implications for hydration? I’ll address these questions and what the research and my experience suggest are the answers in my next blog.

1. Naghii, M.R. “The Significance of Water in Sport and Weight Control.” Nutritional Health 14, no. 2 (2000): 127-132.
2. Convertino, V.A., L.E. Armstrong, E.F. Coyle, G.W. Mack, M.N. Sawka, L.C. Senay Jr., W.M. Sherman. “American College of Sports Medicine Position Stand. Exercise and Fluid Replacement.” Medicine and Science in Sport and Exercise 28, no. 1 (1996): i-vii.
3. American College of Sports Medicine, M.N. Sawka, L.M. Burke, E.R. Eichner, R.J. Maugnah, S.J. Montain, N.S. Stachenfeld. “American College of Sports Medicine Position Stand. Exercise and Fluid Replacement.” Medicine and Science in Sport and Exercise 39, no. 2 (2007): 377-390.
4. Noakes, T. “IMMDA-AIMS Advisory Statement on Guidelines for Fluid Replacement During Marathon Running.” New Studies in Athletics: IAAF Technical Quarterly 17, no. 1 (2003): 7-11.
5. Noakes, T. “Hyponatremia in Distance Runners: Fluid and Sodium Balance During Exercise.” Current Sports medicine report 1, no. 4 (2002): 197-207.
6. Hiller, W.D., M.L. O’Toole, E.E. Fortress, R.H. Laird, P.C. Imbert, T.D. Sisk. “Medical and Physiological Considerations in Triathlons.” American Journal of Sports Medicine 15, no. 2 (1987): 164-167.