# Hydration, fatigue, HR--?



## Gnarly 928 (Nov 19, 2005)

Last weekend I did a tough 12hr race with ~12,500' of elevation gain. An Endurance time trial. It became hot towards the evening, over 90F, and on my last ~30mile lap, I cramped badly. I've never had problems cramping (but I've put out an effort like this one very seldom) so I was reveiwing the data from my Garmin 305 for clues. I notice my average HR went down significantly over the course of 166 miles and 12 hrs.

We ended the race on the same road where we started and I remembered to hit my "lap" function so I got good data readings. My average HR, at the 7am start when well rested and hydrated was 155 and at 5pm (ten hours later) when I cramped, it was down to 133 average. Some of that was likely because I was off the bike for a few minutes trying to walk out my legs, but the graphs show a real fairly steady decline in my HR as the day wore on.

I consulted, before this race, with Hammer Products (they sponsored the event) and was recommended to ingest just 20-24oz of fluid per hour. I've been intaking about twice that(appx 2 w.bottles per hour on hot days) in other hot day races, but I gave that a try this time...until about 2pm when I got real headache-y and began feeling dehydrated..Yeah, too late then, but I resumed drinking 2 bottles per hour, one of Heed, one H2o..and I was taking Hammer's Endurolytes at 2/hr all day. My calorie intake was adequate, again using Hammer products, which I am familar with...I didn't bonk (though some did, for sure)

So was my lower HR a function of dehydration and the heat? Or is that within the normal range of just plain fatigue to see a 20 BPM decline during this type of day long effort? My average speed on that last lap was pretty pathetic, but I did well in the finish order.

(No, I can't afford a power meter right now for all my bikes and wheels.)

Curious,
Don Hanson


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## ericm979 (Jun 26, 2005)

Usually when I am dehydrated or overheated but not tired my HR stays about the same and my power drops. It does get harder to keep the same HR- my brain is probably getting additional distress signals due to dehydration.

Of course your HR drop could just be from getting tired.

Some of the more recent research is that athletes don't need quite as much water as previously thought, and a little dehydration isn't that bad:

http://www.sportsscientists.com/2007/10/fluid-intake-dehydration-and-exercise_21.html


Still set for the Everest Challenge?


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## jgrantv10 (Nov 17, 2005)

I've often experienced something similar on very long (12-24 hour) rides. In these instances, I can't get my HR over ~140-145bpm at all, a condition that can last for long periods of time. Oddly, this doesn't seem to correspond to power (at least not for short busts like powering through rollers or climbing at tempo; it does seem to prevent me from riding at threshold for very long without hurting). My power meter verifies this. I've wondered whether it is just muscle fatigue - as in the heart muscle. In my case, this phenomenon doesn't seem to correspond to either caloric or hydration changes though I haven't ruled out electrolytes.

I agree. Curious.


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## Gnarly 928 (Nov 19, 2005)

ericm979 said:


> http://www.sportsscientists.com/2007/10/fluid-intake-dehydration-and-exercise_21.html
> 
> 
> Still set for the Everest Challenge?


 Thanks for the reference.

I've decided in favor of the Huntsman World Senior Games again rather than the EC this year. The driving time is the same to either, but the Huntsman Games, in St George, Utah is the best age category bike racing in the world...at least according to all the competators I've raced with over the past 5 years I have done the races.

http://www.hwsg.com/cycling.html

Last year in my category there were 2 former national champs and one current Nat Champ (Canada) plus a whole slew of Euros and even some S. Americans. We all agreed it was the most competative racing we'd encountered all season. Plus, rather than just a killer climbing challenge, I'll get 4 different races in four days..A HC TT, a crit, a flat 40ktt and a great 40mile road race..all run with 5 year age groupings and scored as a stage race..kind of..

And next year, I will be in the 65+ class at the Everest Challenge rather than the 50-64 class I'd be in this time out...

Anyhow, thanks for the insights...I, too, didn't feel especially +weak+ with the low HR..It just wouldn't go to my normal max of about 190...which is high, but normal for me..

Don Hanson


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## jgrantv10 (Nov 17, 2005)

Oh man. That looks like a blast. Now you've got me looking forward to the big 5-0 (still a few years yet).


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## Oldteen (Sep 7, 2005)

Multiple possible reasons that HR could be lower. Dehydration & generalized fatigue may contribute. It is also possible your muscle cramping prevented you from putting as much metabolic demand on your cardiopulmonary system late in the ultraendurance event.


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