Interesting point-counterpoint debate in the most recent issue of Med Sci Sports Exerc…I’ll leave it up to interested parties to read it for themselves, but I thought that Dr. Sawka’s concluding statement was right on the money:
“Dehydration (water deficits of >2% BM) consistently degrades aerobic exercise performance in temperate and warm-hot environments. Physiological mechanisms contributing to dehydration-mediated performance degradation include augmented hyperthermia, increased cardiovascular strain, altered metabolic and central nervous system functions, and increased perception of effort. Dr. Noakes may not agree with conventional physiological models explaining dehydration mediated performance degradation, but his alternate notion awaits supportive experimental evidence.”
Hi Andrew, I think the main point that Noakes was originally making was that dehydration will rarely cause death while over hydration leading to hypervolemic hyponatremia is certainly a path down which the athlete can put him/herself at a much higher risk of death. I think most of us will agree that deydration to some % of body mass will lead to impaired performance…but performance and death are too separate things, and I certainly won’t argue against staying close to your regular body mass to maintain optimal performance in racing. But overhydration in North American marathons and IMNA events where there generally are way too many aid stations is a risk that athletes should be aware of. Noakes’ rule of thumb (drink when thirsty) seems to work for myself.
I was waiting for someone to post this little exchange.
Criticism notwithstanding, I did think his reference to data indicating different pacing strategies when the athlete knew fluids would be limited was interesting. In my mind, the question is: Is this a conscious decision, or truly a subconscious pacing strategy? The former would indicate a smart athlete, while the latter would throw more fuel on the central governor fire Noakes has been stoking. (A concept I do find most intriguing, BTW).
That was also the most interesting part in my mind as well (the limiting of pace/exertion when fluids were known vs. unknown). I just went through this recently while on vacation (well, wife’s family reunion). Was doing a planned long run (18-20 miles) from our hotel to their reunion spot. Was 96 degrees and humid. Had a fuel belt with me and was going to stop somewhere along the way to refuel … Ah … well, there was NOTHING. Finally stopped at a farmer’s house to beg for water - seriously. After reading this study I was immediately reflecting upon that experience ;0
Good point…I bet there is a large group of athletes in any Ironman or marathon suffering from impaired performance due to overhydration…or even if it is not overhydration (in the sense of the body retaining too much intra cellular fluid), too much liquid sloshing around in the stomach not being absorbed or going anywhere.
Dr. Noakes does a nice job of presenting contrarian ideas to make us think, look back at the data, and realize what the evidence leads us to. While I haven’t seen the data that thirst decreases performance, I can believe that someone that is thirsty vs someone that is not thirsty might perform worse. However, I think that it is ridiculous to think that performance wouldn’t decline with a 11% decline in BM (as pointed out by Dr. Sawka). Similarily, as it has been proven, a euhydrated subject will perform better in the heat than someone with mild dehydration (>2% loss in BM). As Dr. Sawka pointed out there is clear evidence that dehydration decreases performance via several means (eg. cardiovascular, metabolic). To think that is doesn’t is foolish.
I don’t think that this article was intended to discuss the health/performance benefits of overhydration vs euhydration/dehydration, as the title is “Does Dehydration Impare Exercise Performance?”. While those are issues to explore, that wasn’t the intent here.
Yoinks!!! $400 per year subscription! You guys are pretty serious about this stuff.
A subscription to the journal comes with your membership, which even for me is only $210/y (those still in training pay only $80-155/y).