Wednesday, October 1, 2008

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% [4] but may be as low as 3% in hot conditions [5]. 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 [9]. 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 [10]. 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 [15]. 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.


At October 1, 2008 10:18 AM , Anonymous Anonymous said...

While this makes sense when you consider each of the items individually... when you consider the items together it becomes more complicated. Sodium increases the rate of water absorption... sodium increases the rate of carbohydrate absorption. There are recommendedwater/carbohydrate ratios that are optimum (at some temperature or other)...

At October 1, 2008 2:47 PM , Blogger Dave said...

Maybe it's just me having difficulty changing how I think about hydration, but to me, none of this research sounds conclusive. The articles you cite here conflict with other research.

It always seems to be the case with any medical study... wait long enough and someone will come up with a study that -- intentional or otherwise -- contradicts it.

I certainly appreciate your effort, here Joe. But my takeaway is that I'll still have to listen to what my body (and mind) says works best.

At October 1, 2008 4:57 PM , Anonymous Anonymous said...

Thanks for advocating a "listen to your thirst" common sense approach to this. As a child, I often spent 6-8 hours in hot summer days playing and I never suffered crippling dehydration because I simply drank when thirsty and ate when hungry. The strange formulations of when and how much to drink during endurance events took some of the fun away because it presumes that someone out there is smarter than you are about taking care of yourself. Sometimes that's true but I'm glad that in this case, I can reclaim control over my hydration strategy with confidence.

At October 2, 2008 7:50 AM , Blogger Andy Froncioni said...

Dark urine can also result from myoglobin resulting from damaged muscle tissue. Not all of the coloration in urine is urea.

At October 2, 2008 12:04 PM , Anonymous Anonymous said...

Thanks for revealing your thinking on hydration. Training and racing mostly in Phoenix has made me an "expert" on my own experiences with hydration. One thing I think would be interesting for you to follow up with is the stomach clearance rate. I recall from physiology classes that small amounts of liquid will just sit in the stomach (thus NOT hydrating you) until the volume reaches an amount that activates the lower sphincter muscles into the gut. Thus, many folks that sip drinks may not actually be hydrating themselves as they think. Also, the concentration of fluids will play a role in emptying. I find that bolus drinking (water) (enough to activate the emptying immediately) works best while cycling, but not running. Anyway, I know it is a little off subject but may be interesting to explore.

At October 2, 2008 2:01 PM , Blogger Joe Friel said...

Anon--You know I recall that about faster emptying with more in the stomach from a long time ago myself, but now can't find the research. I've always done that myself--drink fewer large amounts rather than smaller, more frequent amounts.

I did find one study (Rehrer et al, 1990) in which they had triathletes bike and run for 80 minutes at the same relative intensities (70% VO2peak) on different occasions. They found that in the first 40 minutes there was difference in gastric emptying rates when the drinks were isotonic (about 8% carb solution). But in the last 40 minutes there was a faster emptying rate with cycling. With a hypertonic solution (high carb concentration) there was no difference for the entire 80 minutes as the emptying rate was quite slow.

At October 3, 2008 6:32 AM , Blogger Bahzob said...

Thanks again for this series. Like I said on last post it makes sense to me based on personal experience. I will do some tests during training and see what works for me.

Just a suggestion re this. You could try posting a protocol for us to follow that would help us see what works and get some structured (albeit not scientific) feedback. E.g. plan 4 long rides over 4 weeks, spin a coin. Heads rides 1 and 4 use drink when thirsty/2&3 drink 700ml per hour little and often. Tails do it the other way round. (Try to do in same conditions) Look at results (cardiac drift, power, rpe, gastro feeling, post ride exhaustion, time to recover). Any differences?

At October 3, 2008 9:15 AM , Blogger Joe Friel said...

Hi bahzob - An interesting idea but I think I'll let people decide for themselves what works best for them. Thanks for your input. Might help others decide how to best to attack this issue for themselves.

At October 3, 2008 12:01 PM , Anonymous Anonymous said...

Noakes covers extensively the fact that the rate of emptying is a proportional to the amount in the stomach.

At October 3, 2008 12:01 PM , Anonymous Anonymous said...

Noakes covers extensively the fact that the rate of emptying is a proportional to the amount in the stomach.

At October 8, 2008 12:27 AM , Anonymous Will said...

Thanks a lot for posting such valuable information. I must say that this is a great list of FAQs for someone who is looking for answers regarding hydration during exercise. The post is well researched and very well written. It is clear and concise. My son is into long distance events and is always looking for answers to all these questions. So I have asked him to check out your post and also taken a print of it and stuck it in his small gym. I am sure he will appreciate the post as much as I did… Thanks again mate!

At October 10, 2008 12:53 PM , Blogger askan said...

Very interesting serie, thanks a lot! But I don't get why you dislike the idea of taking Sodium supplement during the race. You wrote: "replacing fluid is far more critical", but I don't see any problem in doing both.

At October 12, 2008 8:15 AM , Blogger Joe Friel said...

Hi askan - Thanks for your note. As I said in one of the FAQs, I don't think there's a downside to taking in sodium during exercise. But I also don't think there's an upside.

At December 30, 2008 9:03 PM , Blogger OilcanRacer said...

thanks for your insight and reseach here.

i have a few disaggreements, but mostly in relation to myself and a high metabolism body.

in the past i have suffered with following the norm in nutrition and what was prescribed as best. after many painful years of trial and error i have found a system for us(high revving people) that works for me.

subsecuently i came across the hammer nutrition site and their free advice section. thier nutritional claims where so close to what had worked for me that it seemed i wrote it.

first off this is not an endorsment for their products, just their explination of body nutritional needs.

here are a few tidbits:

the body can only absorb so much water and nutrition per hour.

over feeding while exercising leads to bloating or a hypertonic state.

20-30 ounces of water an hour.

carbs/protien in a 3 to 1 ratio after one hour of intense exercise.

same ratio for recovery right after work-out

not all carbs and protiens absorb at tne same rate. pick the ones that work for you. longer chains are better.

the stomach does need a full gulp or more to pass into the intestines.

drinking and eating when feeling the need for me leads to irratic consumption and loss of effenciency.
using rate of exertion works better with minimal time periods for longer easier rides. twice an hour for water and carbs.

buffering lactate works wonders if done correctly.

thanks agian for your site and all the work you do. please keep it up. you help all of us.


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