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) . Around 4-5% losses do seem to have negative consequences, however . 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 . 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.