For seasoned runners....

- Less than half the weight you lose during exercise is due to water loss. Weighing yourself before and after exercise is pointless unless you're just curious.

- The only correlation between how fast runners are and dehydration, is that the faster the runner the more dehydrated they will be. Studies have shown that the more dehydrated runners are the winners while the least dehydrated are those in the back of the pack. Haile G. dropped 10% of his weight when ran his 2:03:59 marathon. The percent of weight loss that will ‘cause a decrease in performance has yet to be reliably determined.


- No one here has ever been dehydrated enough that it hurt their performance, ever.


Google ‘Tim Noakes dehydration’ if you disagree with any of these facts I’ve presented.

- Less than half the weight you lose during exercise is due to water loss. Weighing yourself before and after exercise is pointless unless you're just curious.

- The only correlation between how fast runners are and dehydration, is that the faster the runner the more dehydrated they will be. Studies have shown that the more dehydrated runners are the winners while the least dehydrated are those in the back of the pack. Haile G. dropped 10% of his weight when ran his 2:03:59 marathon. The percent of weight loss that will ‘cause a decrease in performance has yet to be reliably determined.


- No one here has ever been dehydrated enough that it hurt their performance, ever.


Google ‘Tim Noakes dehydration’ if you disagree with any of these facts I’ve presented.

re: weighing yourself - Disagree - it is a valid manner to estimate water lost via sweat. I just recently had this suggestion from person, former olympian and current nutritionist to NCAA athletes and she is a PHD. I'll trust her on that. In addition, that is basically what race officials are doing in events such as Badwater or other ultra races. I think they have a bit of experience with dehydration.

Re: dehydration being related to speed. I would think that the higher % of weight lost has more to do with the elite athletes overall lower body weight and better ability to preload glycogen stores for the event vs. speed.

Also you say "The percent of weight loss that will ‘cause a decrease in performance has yet to be reliably determined" and then "No one here has ever been dehydrated enough that it hurt their performance, ever". - those statements are contrary to each other. In addition, it is pretty simple logic to understand that a decrease in hydration = a decrease in blood volume (since it is made up of a lot of water). Decreased blood volume means that getting oxygen to your muscles is harder. Here is a link to some information for that. http://www.humankinetics.com/excerpts/excerpts/dehydration-and-its-effects-on-performance

Good summary below of it:
Fatigue toward the end of a prolonged sporting event may result as much from dehydration as from fuel substrate depletion. Exercise performance is impaired when an individual is dehydrated by as little as 2% of body weight. Losses in excess of 5% of body weight can decrease the capacity for work by about 30% (Armstrong et al. 1985; Craig and Cummings 1966; Maughan 1991; Sawka and Pandolf 1990).

Thank you for everyones replies. There is alot of good information in your comments. I don't think I drink as much water as I should, in general. If I did, maybe I would have better luck like some people. I don't really "Want" to run 10 miles without water, however, it would be nice to know that I could. Maybe it would be good to build up my tolerance. I suppose you never know when you'll have to run for your life without your favorite pair of running shoes and 80 oz. of water on your back.:laugh:

So much misinformation, so little time.

- First off, heatstroke/heat illness, whatever you call it, is not caused by dehydration. It’s caused by the environment you’re exercising in and the intensity of your exercise. Hydration DOES NOT play a part.

- Less than half the weight you lose during exercise is due to water loss. Weighing yourself before and after exercise is pointless unless you're just curious.

- The only correlation between how fast runners are and dehydration, is that the faster the runner the more dehydrated they will be. Studies have shown that the more dehydrated runners are the winners while the least dehydrated are those in the back of the pack. Haile G. dropped 10% of his weight when ran his 2:03:59 marathon. The percent of weight loss that will ‘cause a decrease in performance has yet to be reliably determined.

- You drink to thirst. That’s the best way, period.

- No one here has ever been dehydrated enough that it hurt their performance, ever.

- The last long run I did, I ran 20 miles, four 5 mile loops, with each loop faster than the previous. It was around 70 and sunny. Was able to get the last loop in under 7 min/mile pace. I never drink or eat during a run, my body doesn’t ask for it, therefore, I don’t force my body to take it.

- No one ever needs to ever carry any fluid during a race as long as the race has water stops.

- 7 signs of drinking too much fluid:
1. Impaired performance
2. Nausea and vomiting
3. Headache
4. Altered level of consciousness
5. Seizure
6. Bloating/Swelling of hands, legs and feet
7. Muscle cell breakdown (rhabdomyolysis) with the development of acute kidney failure

Symptoms NOT caused by dehydration:
1. Dizziness and fainting
2. Cramps
3. Wheezy breathing
http://www.humankinetics.com/excerpts/excerpts/seven-clear-symptoms-of-exercise-associated-hyponatremia

Google ‘Tim Noakes dehydration’ if you disagree with any of these facts I’ve presented.

Thank you for everyones replies. There is alot of good information in your comments. I don't think I drink as much water as I should, in general. If I did, maybe I would have better luck like some people. I don't really "Want" to run 10 miles without water, however, it would be nice to know that I could. Maybe it would be good to build up my tolerance. I suppose you never know when you'll have to run for your life without your favorite pair of running shoes and 80 oz. of water on your back.:laugh:

So much misinformation, so little time.

- First off, heatstroke/heat illness, whatever you call it, is not caused by dehydration. It’s caused by the environment you’re exercising in and the intensity of your exercise. Hydration DOES NOT play a part.

- Less than half the weight you lose during exercise is due to water loss. Weighing yourself before and after exercise is pointless unless you're just curious.

- The only correlation between how fast runners are and dehydration, is that the faster the runner the more dehydrated they will be. Studies have shown that the more dehydrated runners are the winners while the least dehydrated are those in the back of the pack. Haile G. dropped 10% of his weight when ran his 2:03:59 marathon. The percent of weight loss that will ‘cause a decrease in performance has yet to be reliably determined.

- You drink to thirst. That’s the best way, period.

- No one here has ever been dehydrated enough that it hurt their performance, ever.

- The last long run I did, I ran 20 miles, four 5 mile loops, with each loop faster than the previous. It was around 70 and sunny. Was able to get the last loop in under 7 min/mile pace. I never drink or eat during a run, my body doesn’t ask for it, therefore, I don’t force my body to take it.

- No one ever needs to ever carry any fluid during a race as long as the race has water stops.

- 7 signs of drinking too much fluid:
1. Impaired performance
2. Nausea and vomiting
3. Headache
4. Altered level of consciousness
5. Seizure
6. Bloating/Swelling of hands, legs and feet
7. Muscle cell breakdown (rhabdomyolysis) with the development of acute kidney failure

Symptoms NOT caused by dehydration:
1. Dizziness and fainting
2. Cramps
3. Wheezy breathing
http://www.humankinetics.com/excerpts/excerpts/seven-clear-symptoms-of-exercise-associated-hyponatremia

Google ‘Tim Noakes dehydration’ if you disagree with any of these facts I’ve presented.

Wow some bold claims. If being dehydrated doesn't hurt performance, why does a race need to have water stops at all?

So I read more on this on The Science of Sport blog and it seems maybe there is some truth in all this.

http://www.sportsscientists.com/search?q=dehydration

Anyways today I conducted a little n=1 experiment. It was sunny, upper 70s, and 75% humidty and I ran 10 miles. I drank 2 8oz cups of coffee in the hours beforehand, no other fluids, and ate nothing and ran completely fasted. I brought one 16.9oz bottle of water with the intention of drinking only when I feel thirsty.

I ran at marathon pace (8:20/mile), which is about 20 secs/mile slower than my normal comfortable training pace for this distance. It definitely slowed to about 8:30s in the last mile or two, but I never felt awful. I sweat profusely on days like this and today was no different. Both my shirt and shorts were completely drenched.

Typically I might occasionally slow down to a crawl after mile 8 on a day like this when I am pre-emptively hydrating myself in anticipation that it will catch me off guard (Based on the notion that if you wait til you are thirsty, its too late).

Anyways by the end of the run I only drank about 1/3 of the water ~5.6oz because I just never got very thirsty. I'd say there's definitely a good chance that the body really is capable of managing fluids and electrolytes appropriately and that over-hydrating may very well be a reason for hindered performance during hotter temperatures.

Thank you for everyones replies. There is alot of good information in your comments. I don't think I drink as much water as I should, in general. If I did, maybe I would have better luck like some people. I don't really "Want" to run 10 miles without water, however, it would be nice to know that I could. Maybe it would be good to build up my tolerance. I suppose you never know when you'll have to run for your life without your favorite pair of running shoes and 80 oz. of water on your back.:laugh:

So much misinformation, so little time.

- First off, heatstroke/heat illness, whatever you call it, is not caused by dehydration. It’s caused by the environment you’re exercising in and the intensity of your exercise. Hydration DOES NOT play a part.

- Less than half the weight you lose during exercise is due to water loss. Weighing yourself before and after exercise is pointless unless you're just curious.

- The only correlation between how fast runners are and dehydration, is that the faster the runner the more dehydrated they will be. Studies have shown that the more dehydrated runners are the winners while the least dehydrated are those in the back of the pack. Haile G. dropped 10% of his weight when ran his 2:03:59 marathon. The percent of weight loss that will ‘cause a decrease in performance has yet to be reliably determined.

- You drink to thirst. That’s the best way, period.

- No one here has ever been dehydrated enough that it hurt their performance, ever.

- The last long run I did, I ran 20 miles, four 5 mile loops, with each loop faster than the previous. It was around 70 and sunny. Was able to get the last loop in under 7 min/mile pace. I never drink or eat during a run, my body doesn’t ask for it, therefore, I don’t force my body to take it.

- No one ever needs to ever carry any fluid during a race as long as the race has water stops.

- 7 signs of drinking too much fluid:
1. Impaired performance
2. Nausea and vomiting
3. Headache
4. Altered level of consciousness
5. Seizure
6. Bloating/Swelling of hands, legs and feet
7. Muscle cell breakdown (rhabdomyolysis) with the development of acute kidney failure

Symptoms NOT caused by dehydration:
1. Dizziness and fainting
2. Cramps
3. Wheezy breathing
http://www.humankinetics.com/excerpts/excerpts/seven-clear-symptoms-of-exercise-associated-hyponatremia

Google ‘Tim Noakes dehydration’ if you disagree with any of these facts I’ve presented.

Wow some bold claims. If being dehydrated doesn't hurt performance, why does a race need to have water stops at all?

So I read more on this on The Science of Sport blog and it seems maybe there is some truth in all this.

http://www.sportsscientists.com/search?q=dehydration

Anyways today I conducted a little n=1 experiment. It was sunny, upper 70s, and 75% humidty and I ran 10 miles. I drank 2 8oz cups of coffee in the hours beforehand, no other fluids, and ate nothing and ran completely fasted. I brought one 16.9oz bottle of water with the intention of drinking only when I feel thirsty.

I ran at marathon pace (8:20/mile), which is about 20 secs/mile slower than my normal comfortable training pace for this distance. It definitely slowed to about 8:30s in the last mile or two, but I never felt awful. I sweat profusely on days like this and today was no different. Both my shirt and shorts were completely drenched.

Typically I might occasionally slow down to a crawl after mile 8 on a day like this when I am pre-emptively hydrating myself in anticipation that it will catch me off guard (Based on the notion that if you wait til you are thirsty, its too late).

Anyways by the end of the run I only drank about 1/3 of the water ~5.6oz because I just never got very thirsty. I'd say there's definitely a good chance that the body really is capable of managing fluids and electrolytes appropriately and that over-hydrating may very well be a reason for hindered performance during hotter temperatures.

Great test. Do you consider "70 degrees" hot weather? Personally, I know I wouldn't need but a few sips of water on a 10mile run (just to wet my throat) in 70 degrees. Conduct that test in 90+ degree weather, and see if your results vary. I'm guessing the added heat will demand more fluid replacement.