Physiological adaptations and dehydration

Felt_Rider

3 State 3 Mountain starting in Chattanooga, Tn with 2,500 riders from across the nation. It should be fun if the storms blow through early.

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frenchyge

Good info, thanks! It's always great when the researchers will take some time to clarify their findings.

There's also the issue of knowing what hydration level the body is starting from before exercise. I would expect fluid intake during the few days before an event have as much of an effect (if not greater) than what is actually consumed during the event. I notice differences in daily urine concentration without accompanying differences in thirst.

Obviously fatigue is going to reduce the metabolic rate during long events, but I'm wondering more about heat exhaustion, which the articles seemed to indicate had only a casual relationship with hydration.

That all makes sense regarding core temperature, but heat accumulation depends on the balance between heat generation and heat rejection. During an event, ambient temperature probably rises (reducing heat rejection) and hydration levels probably drop (tendency to replace ~50% of losses through drinking), even if metabolic rate is fairly steady. So, if an athlete suffers from heat stress or heat exhaustion in the latter part of an event, it sure seems like their ability to reject heat has dropped off to the point that they are no longer able to match the heat generation levels that they've been maintaining, and that core temperature is building as a result. With evaporation being the body's primary means of heat rejection, it sure seems reasonable to point at dropping hydration levels as the cause for the mismatch between heat generation and rejection later in the event.

I guess what I'm saying is that a body is able to effectively regulate its temperature at the beginning of a long event, but then loses that ability as the day wears on. If that's not as a result of dropping hydration levels, what is the cause?

I'll do that, thanks!

Sports Scientis

Hi Felt-Rider

Ross Tucker here, from the Science of Sport. Sorry for the delay in replying, been busy at those other posts, which are causing some fatigue of their own!

I think that conditioning is a major factor. A study was published last year by Collins and Schwellnus et al. that looked at factors associated with cramp, and three of them are all indicative of conditioning being "inadequate" for the level of performance being attempted. They were: Racing, going further/longer than ever before, and much more challening terrain than is encountered during training.

These are all, no doubt, obvious, but they all point to fatigue as a cause of cramp - as we discussed last year in our cramp series, the new theory for cramp is that it's caused by a "malfunction" in the nerves and reflexes that control the muscle. The post is here:

http://scienceofsport.blogspot.com/...p-part-iii.html

This is made far worse by fatigue, and so my suspicion is that your problem is related to fatigue, brought on by "weak" muscle at that late point in your rides.

One thing that might help is to anticipate the cramp and stretch in advance. You'll recall (or can read that post) that cramp is alleviated by stretching, which restores the "normal" reflex control of the muscle. So I believe that stretching in anticipation of cramping may assist you slightly, and perhaps even prevent the cramp from occurring!

Hope that helps a little!
Ross

acoggan

New?

Sports Scientis

OK, fair enough, if you want to call me out on it. Define "new" though...? If I'd said "newer", in contrast to the old "salty sweater" theory, would that suffice...?

sogood

Not so simple. Altitude training is well known to induce adaptation. So I don't think it's a good counter-argument here.

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swampy1970

It depends if you were referring to the Druids having cramps erecting the sarsen trilithons at Stonehenge, then "newer" would be apt.....

swampy1970

9,000ft of climbing, including a climb called Suck Creek (I just had to laugh at that) will give you some fun over 100 miles.

There's no prizes for blasting up the hills. Take it at your own pace when the climbs start and err on the side of caution.... and have fun! Hope the weather stays good.

Sports Scientis

Or perhaps the construction workers on the Hoover Dam Project, some 75 years ago. Before that, the first "evidence" of the salt theory for muscle cramp came from labourers in the mines, who were found to have salt in their sweat over 100 years ago. That, combined with the observation that construction workers recovered when the drank salty milk, helped "establish" that cramp occurred due to lowered salt content caused by dehydration. Never mind the fact that no one ever looked at the salt content of people who did not cramp, or the intracellular or plasma electrolytes in those people who did not cramp. Subsequently, turns out that crampers are actually less dehydrated than non-crampers, at least according to the indirect measurement of body weight changes before and after exercise.

The theory that muscle cramp is caused by disinhibition of the Golgi tendon organs, combined with increased activity of the muscle spindles, was first proposed in a research publication in 1997. I'd say that "new" is probably appropriate, given that one theory has its origins 100 years ago, while the other is 11 years ago. But then if we look at the druids, that's even more appropriate!!

acoggan

I think you need to dig into the literature a bit deeper. I recall this theory of cramping being discussed when I was in graduate school, and that was >25 y ago.

Sports Scientis

Do share the origins then...I have provided a reference for it, perhaps you might do the same, rather than recollections from 25 years ago.

Sports Scientis

Schwellnus MP, Derman EW, Noakes TD.

Aetiology of skeletal muscle 'cramps' during exercise: a novel hypothesis.
J Sports Sci. 1997 Jun;15(3):277-85. Review

Felt_Rider

Ross, thanks for the reply and thankfully I did begin stretching starting Thursday and Friday before doing a century yesterday. I do believe it helped. I had one moment about mile 90 when my hamstring felt like it was going to cramp, but I dropped to a lower gear, spinned lightly and within a few minutes I was back to normally without getting a cramp.

Thanks again for the reply and reference link.

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acoggan

Try Herbet DeVries textbook.