Physiological adaptations and dehydration

daveryanwyoming

Agreed, the original research points out problems at either extreme but doesn't help that much in terms of real world hydration strategies. The Hammer Nutrition piece linked above and other stuff on their site and in their printed material gives specific guidelines but you've got to consider the source, their philosophy and perhaps their marketing agenda.

Still I find their advice of limiting your fluid intake to 20 ounces per hour for typical weather conditions with broad based electrolytes (more than just sodium and potassium) to be pretty reasonable. They also strongly push the idea that everything we do nutritionally during training and racing is a deficit game and attempts to consume anything at our burn rate are counterproductive. IOW, you will eventually run out of glycogen and you will eventually become dehydrated and you'll eventually run out of electrolytes the trick is to delay those problems as long as possible, get to the finish line and then replenish post event.

They make a pretty good argument for their approach and it holds up with other references like Monique Ryan's work (no relation), Dan Bernadot's "Advanced Sports Nutrition", Suzanne Eberle's "Endurance Sports Nutrition", etc. It also holds up pretty well with what's reasonable during races, 200-300 Calories per hour, 20 ounces of fluid per hour, those are typically what I can manage during hard racing or training.

But I agree, read too many studies and it's hard to know what to do....

-Dave

acoggan

Based on work from Coyle's lab, the answer appears to be "none".

swampy1970

Come down here (near sunny Sacramento, CA) and we can go for a 4 hour ride around Lake Berryessa and take in the big hills and get about 5000ft of climbingin during mid June/July when it's around 100F.... If you're wiser than the average bear you get up at 5.30am when its 'only' in the mid 70's and get back when the heat starts to kick in.

But... you can ride in that heat, some of us have no choice. At that time of year the Profile Design behind the seat dual water bottle doohicky comes out and I take 4 bottles with me....

I dig the Hammer Nutrition products. They seem to work well for me and don't taste to bad either. If only they sold the Science in Sport drinks here in the US. That stuff was great.... UK only though it would seem.

Spunout

Reminds me of a joke: What is the difference between an oral and an anal thermometer?

frenchyge

I'm afraid to ask. What?

TheDarkLord

A pretty tasteless joke IMO... (btw, the answer is supposed to be "the taste")

Sports Scientis

Great discussion going on here, if I can just try to clarify some of the points since you are talking about our posts on The Scienec of Sport.

It is difficult to know about hydration level only because sports drink companies give us so much erroneous information. In fact our thirst is the best indicator of our fluid needs and is very senstitive to changes in our fluid balance.

Currently we are doing a series on fatigue. . .it is a complex issue, but suffice to say that a number of different things serve as inputs to the system that will alter the exercise intensity (i.e. your pacing strategy).

Our research suggests that it is the rate of heat accumulation that will make you slow down in the heat, and not how dehydrated you are.

In one study from my doctortal work, we showed that ingesting fluid at rates lower than to thirst resulted in a 3.1% performance decrement over an 80 km cycling time trial in the heat. In those trials the guys drank 33% or 0% of their sweat losses, or rinsed their mouth with water in the other trial.

(NB: when drinking to thirst we tend to replace about 50% of our losses.)

Indeed, there is an effect of fluid ingestion on both temeprature regulation and exercise performance, and this is in the range of 3% when restricting fluid intake. In the same trial I mentioned above, when the guys drank volumes higher than thirst (66% and 100%) they did not cycle any faster compared to the thirst trial.

The one main point is that dehydration does not cause you to get too hot, and fluid ingestion will not keep you cool. Rather it is the metabolic rate that predicts your core temperature.

Is there an effect of fluid ingestion on the temp regulation? Yes, but all the brain does is slow you down a bit (~3% in the 80 km TT's) so that you finish with an identical temperature response. Therefore there is a definitely benefit of ingesting fluid (to thirst) during endurance exercise. However, ingesting fluid at higher rates than to thirst does not result in even faster performance.

The interesting finding from that study was that regardless of how much each subject ingested, his core temperature at the end of each time trial was almost exactly the same. Some subjects finished at 40 C and some hardly cracked 39 C, but it was highly repeatable for each cyclist.

Great discussion going on here, and I encourage you to read the current series we are doing on fatigue. It is generating heaps of debate and some really great questions after only a couple of days.

Kind Regards,
Jonathan Dugas

Felt_Rider

I will enjoy reading the fatigue series.

I have a question while you are here about the hydration series.
Did I imagine in the hydration series or elsewhere on your blog that cramping is sometimes caused by one reaching the limitations of conditioning? I wanted to reference a friend to the statement, but I could not find the statement.

The reason I ask is that I ride with guys that are above my level and toward the end of the ride I begin to get cramps. Often these veterans keep telling me to hydrate and use electrolytes, which I do but the cramps occur anyway. I can typically keep their pace on a ride less than 60 miles, but I seem to start getting cramps if the ride is 70 or 80 at their pace. I have told them that I am drinking enough and using enduralytes (mainly to please them), but they don't believe me when I say that I think it is my conditioning is not up to their level.

Or am I way off base in the assumption?

__________________
My Blog

Spunout

Winner, Ding Ding Ding! Please check with polar.fi to claim your prize.

Spunout

This is probably the best explanation for cramps.

Steve_B

Try taking in more calories before and during the ride as well. It made a huge difference in my cramping issues. The highlighted statement above suggests to me that you may be running out of glycogen.

Felt_Rider

Thanks
I have been trying to make the effort to increase glycogen intake lately and I will see how things go tomorrow on a century. The pace will much slower than our usual, but we have a lot of climbing.

__________________
My Blog

swampy1970

... ah, good ol' bottled glycogen. (Glycogen Protein Balance - no less!)

With added bubbles for a "postive lift weight reduction"

Felt_Rider

I can definately use that at mile 82, which will be the hardest climb that I will have faced in my short cycling history.

__________________
My Blog