Effect of weight loss (dehydration) and muscle break down on performance
by on Friday, April 5, 2013  (2 comments)


Writing about another study (I promise this blog won't become all about reviewing studies but this will be a part of it). This time, a study of how weight loss as a proxy for dehydration and myoglobinuria as a proxy for muscle breakdown are related to reduction in muscle power. Essentially, the idea of this study is to determine what the correlation is between late race muscle fatigue and two commonly held explanations for that muscle fatigue.

In a break from commonly held assumptions, body mass loss (the proxy for dehydration) did not seem to affect muscle power output. Participants in the study ranged from gaining body mass to losing more than 4% of body mass (that would be 6 pounds for a 150 pound person) during a marathon but loss of power output was not correlated with body mass loss.

On the other hand, there is a quite strong correlation between myoglobinuria production (the proxy for muscle breakdown) and muscle fatigue.

What does this tell us? Well, I would still strongly suggest not ignoring fluids during a marathon, especially a warm weather marathon. However, don't go to extremes. I recall a few individuals telling me that I should follow their hydration plans because they actually gained weight during marathons. Why should we believe that this is ideal? It's been shown that the best marathoners tend to lose weight during marathons, typically in the range of 5% of body weight but some even more. Now, we have more evidence that this singular focus on hydration may not help.

Instead, we should be focused on not breaking down our muscles. So how do we do that? We train our muscles. Nothing all that new here. Lots of long runs, lots of volume at faster paces. In addition, though, I think this suggests again the importance of not going out too fast. If you go out too fast, your muscles are going to break down earlier. This will reduce their ability to keep performing at an optimal level earlier than if you go out on pace or even negative split a bit.

With Boston coming, here's another thought. The early miles are downhill. Getting too carried away on early downhills will damage your muscles, especially the quads, even more. We all know (I hope) it's important to not get too carried away early at Boston. This likely explains one reason for that. Your muscles will break down earlier and you'll again lose your ability to perform at an optimal level earlier than if you play it safe on the early downhills.

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I found this interesting. It almost seems counterintuitive in regards to the hydration issue. However, I guess that for some people that 4% or 5% of body mass (fluid loss) is not a case of severe or extreme dehydration. This might not be the case (and is likely not the case) for all individuals.

Therefore, with this extra bit of knowledge the idea of finding out what works best for you in training and not altering from that on race day will help you achieve your best results.

On another note, I have been considering running a race course that I live in the middle of backwards, to take the steep hills down early to strengthen and condition my legs (beat them up) and then run the course in the normal direction to force myself to climb those hills after tiring my legs out. However, we will see what Coach Ryan has to say about that idea.

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It doesn't seem that counterintuitive to me for a few reasons.

1) While 4% may seem like a lot, most marathoners are starting overhydrated. They won't be hurt by the first 1-2 pounds of weight loss because that's just excess fluids.

2) Something most people don't take into account. Glycogen stored in the body is stored with a lot of water. When the glycogen gets burned, that water is released into the body. Free water along the way. This can be excreted without ill effects.

3) While we've been told to fear any level of dehydration, mild dehydration isn't a big deal. You don't want to start dehydrated but dipping a little low by the end isn't necessarily harmful.

I think the real lesson here is that we don't need to fear mild dehydration and we definitely shouldn't be looking to put on weight during a marathon. We should expect some weight loss and not consider it a negative. Of course, we do want to practice everything in training and it would be wise to make part of that figuring out how much weight you lost when you feel good at the end of a long run vs. how much weight you lost when you crashed. You might find a correlation that would be useful to keep in mind on race day.

Ross Tucker at http://www.sportsscientists.com/ (a site I am a regular reader of) has written a few times on the overemphasis of hydration in marathons and the harms of that. He has ample evidence to back it up and my personal experience has been along the same line. Too many people worry way too much about pushing far too many fluids. Tucker says going by thirst isn't nearly as bad of an idea as people say it is.

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