Hydration and Exercise, Part 4
This is the last of a 4-part series on hydration during exercise. Again, I understand that what I’ve been telling you probably contradicts all you’ve been told over the years. I wouldn’t expect you to make a sudden and complete change in how you hydrate during exercise, especially if you’ve had great success in racing. But if you’ve had difficulty with performance in longer events then you may well want to reconsider what you do in this area. Feel free to post your reactions, comments and questions.
Q: What should I drink during a race?
A: It depends on the duration (not necessarily the length) of your race. For shorter endurance events, which I’ve been calling those under four hours, drink either water or a sports drink. Up to about 1.5 to 2 hours, depending on your fitness level, water will do fine. Unless you are in very poor physical condition, it is unlikely that you will bonk (run out of carbohydrate). From this duration up to about 4 hours any sports drink you like the taste of will do the job. Or you may use water and gels. You will need some calories at this duration. Just drink to thirst and you should get both fluid and fuel right. For events lasting longer than about 4 hours I’d recommend separating the hydration and refueling matters. In other words, drink fluids, especially water, to quench thirst using thirst as a gauge of when and how much to drink. You must pay attention to your body to do this. If you become externally focused for long periods of time, which I realize is certainly possible in a race, you are likely to fall behind and mismanage the rate at which you dehydrate. Drinking to an arbitrary schedule in long events is likely to start you down a path toward hyponatremia with performance-detracting symptoms appearing well before you reach the sodium concentration level associated with the condition. Some dehydration is normal and to be expected.
Q: So in long events and workouts what should I use for refueling?
A: Treat refueling as a separate matter from hydration in events longer than about 4 hours. Take in carbohydrate in a form and at a rate you find works for you in training. Again, gels since they are generally easily digested and carried may be a good option for those athletes performing at a relatively high intensity level in four-hour and longer events. If you are familiar with WKO+ software I’d suggest this is an Intensity Factor (IF) of about 80% or higher. If your intensity is lower and less stressful than that then you may well be able to digest sports bars or real food. The slower you go and the lower the IF, the more options you have for refueling. If you are casually walking a marathon a hamburger with French fries will probably work, although I wouldn’t recommend it!
Q: How much dehydration is acceptable?
A: As mentioned in Part 1 of this series on hydration, the number keeps rising in the scientific community. A 2% loss of body weight during exercise was once considered to be a critical level with the experts believing this would result in a significant drop in performance. The research does not support this [1,2,3]. Now that level appears to be something more in the range of 4-5%  but may be as low as 3% in hot conditions . Other studies of Ironman triathletes found no connection between body weight changes and the finishing times of participants [6,7,8].
Q: Should I drink extra amounts in the days and hours leading up to a race in hot conditions so that I’m hyperhydrated?
A: Your body does not store water like a camel’s does. If you drink an excessive amount, meaning more than necessary to quench thirst, you will soon urinate to remove the excess. And by drinking excessively this you temporarily dilute electrolyte stores. So there is nothing to be gained by drinking copious amounts of fluids the day before or the morning of a race . Thirst is the key. Pay attention to your body.
Q: Should I supplement with sodium capsules during an ultra event?
A: For long events like Ironman triathlons, other similar duration ultra-endurance races and slow marathons I don’t see a reason to do this. Sweating at an average rate of 1 liter per hour with an average sodium loss of 40mmol/l produces a sodium loss of about 920mg per hour, about 1 gram. So taking in 1 gram per hour of sodium for, let’s say, 10 hours means you would take in about 10g and lose about 10g. That 10g represents less than about 8% of an average-sized male’s total sodium stores. But realize that losing 10 liters of water in sweat means a loss of perhaps 20-25% of that athlete’s body fluids. That is a much bigger issue than sodium replacement. So replacing part of this fluid is a far more critical issue than sodium replacement.
It’s also interesting to note that sodium loss is not straight line during exercise. As sodium is lost through sweat the rate at which sodium is lost decreases over time to maintain body fluid homeostasis . In other words, at one hour into an event you may well be losing sodium at a higher rate than you are later in the race even though the sweat rate remains constant.
Q: Is there a downside to taking a sodium supplement during a long race?
A: If you take in a small amount of sodium, let’s say that means less than 1 gram per hour, I suspect there is not a significant impact either way on health or performance.
Q: How do I know if I am dehydrated after a workout or race?
A: Most of the research seems to support the notion that a yellow urine color is a good indicator of significant dehydration [11,12,13,14], but not all of the research is in agreement . While having yellow urine may indicate some level of dehydration, such a color by itself is not proof of dehydration. Metabolites, the end products of metabolism such as urea, are often expelled in the urine and provide color even though you are well hydrated. The same goes for B vitamin supplements. They will provide a bright, yellow color to your urine. The best indicator of dehydration is thirst. It works. Just pay attention.
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. Food and Nutrition Board of the Institute of Medicine. “Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate.” Washington DC: The National Academies Press, 2005.
3. 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.” Medicine and Science in Sports and Exercise 39, No. 2 (2007): 316-322.
4. 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.” Medicine and Science in Sports and Exercise 37, No. 8 (2005): 1387-1394.
5. 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.
6. Laursen, P.B., R. Suriano, M.J. Quod, H. Lee, C.R. Abbiss, 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.
7. Sharwood, K., M. Collins, J. Goedecke, G. Wilson, T. Noakes. “Weight Changes, Sodium Levels, and Performance in the South African Ironman Triathlon.” Clinical Journal of Sports Medicine 12, No. 6 (2002): 391-399.
8. Sharwood, K., M. Collins, J. Goedecke, G. Wilson, T. Noakes. “Weight Changes, Medical Complications, and Performance During an Ironman Triathlon.” British Journal of Sports Medicine 38, No. 6 (2004): 718-724.
9. Sawka, M.N., S.J. Montain, W.A. Latzka. “Hydration Effects on Thermoregulation and Performance in the Heat.” Comp Biochem Physiol A Mol Integr Physiol 128, No. 4 (2001): 679-690.
10. Hew-Butler, T.D., T.D. Noakes, S.J. Soldin, J.G. Verbalis. “Acute Changes in Arginine Vasopressin, Sweat, Urine and Serum Sodium Concentrations in Exercising Humans: Does a Coordinated Homeostatic Relationship Exist?” British Journal of Sports Medicine (Epub ahead of print).
11. Armstrong, L.E., C.M. Maresh, J.W. Castellani, M.F. Bergeron, R.W. Kenefick, K.E. LaGasse, D. Riebe. “Urinary Indices of Hydration Status.” International Journal of Sports Nutrition 4, No. 3 (1994): 265-279.
12. Kavouras, S.A. “Assessing Hydration Status.” Current Opinions in Clinical Nutrition, Metabolism and Care 5, No. 5 (2002): 519-524.
13. Shirreffs, S.M. “Markers of Hydration Status.” Journal of Sports Medicine and Physical Fitness 40, No. 1 (2000): 80-84.
14. Armstrong, L.E., J.A. Soto, F.T. Hacker Jr., D.J. Casa, S.A. Kavouras, C.M. Maresh. “Urinary Indices During Dehydration, Exercise, and Rehydration.” International Journal of Sports Nutrition 8, No. 4 (1998): 345-355.
15. Kovacs, E.M., J.M. Senden, F. Brouns. “Urine Color, Osmolality, and Specific Electrical Conductance Are Not Accurate Measures of Hydration Status During Postexercise Rehydration.” Journal of Sports Medicine and Physical Fitness 39, No. 1 (1999): 47-53.