Physiological adaptations and dehydration
- Thread starter tonyzackery
- Start date
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.frenchyge said:
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).frenchyge said:
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.frenchyge said:
(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.frenchyge said:
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
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?
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?
ThanksSteve_B said:
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.
... ah, good ol' bottled glycogen. (Glycogen Protein Balance - no less!)Felt_Rider said:
With added bubbles for a "postive lift weight reduction"
I can definately use that at mile 82, which will be the hardest climb that I will have faced in my short cycling history.swampy1970 said:... ah, good ol' bottled glycogen. (Glycogen Protein Balance - no less!)
With added bubbles for a "postive lift weight reduction"
Where's the ride at? Sounds like it could be fun.Felt_Rider said:I can definately use that at mile 82, which will be the hardest climb that I will have faced in my short cycling history.
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.swampy1970 said:
Good info, thanks! It's always great when the researchers will take some time to clarify their findings.
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?
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.Sports Scientis said:
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.Sports Scientis said:
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.Sports Scientis said:
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 said:
Hi Felt-RiderFelt_Rider said:
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/2007/11/muscle-cramp-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
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...?acoggan said:
It depends if you were referring to the Druids having cramps erecting the sarsen trilithons at Stonehenge, then "newer" would be apt.....Sports Scientis said:
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.Felt_Rider said:
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.
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.swampy1970 said:
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!!
Similar threads
