I understand going into this post that a few people will probably disagree with what I have to say. But, I feel it’s important, as someone who coaches others to be more successful distance runners, to break with conventional wisdom when there’s evidence to do so. As I am an evidence-based rationalist to my core, this is one very good example of that. I’d love for this post to lead to some constructive debate, so if you have links to other scientific examples like those I’m including, please comment with them. Preamble over…on to the post.
Leg muscle cramping is a big issue for runners, and it particularly gets a lot of play in marathon and ultramarathon circles. When cramps hit, there’s really nothing you can do but walk. The traditional argument for the causes of cramping boils down to one or both of the following factors:
- Electrolyte depletion
So the common prevention steps are to drink plenty of fluids and take electrolyte supplements (either in the drink or via tabs, capsules, etc.). And in the case where cramps start to cause problems during a long run or race, the traditional reaction is to try to offset them by replenishing fluids and electrolytes.
I’ve got issues with the cause argument, the prevention approach, and the proposed fix. Let’s take each in turn.
On the causes of cramping during extended bouts of exercise, there is now a more focused body of research to draw upon. There are several good studies that have been carried out under a variety of settings, and here are three that summarize quite well what I currently believe (chosen because they are free downloads so everyone can take a deeper look, should they wish):
- http://www.ncbi.nlm.nih.gov/pubmed/15970952 This study measured the incidence and time to onset of calf cramps in a laboratory setting with groups that were either given a carbohydrate-electrolyte drink or not. While there was a difference in time to onset of cramps (longer for the carbohydrate electrolyte drink group), the incidence of cramps was the same across both groups. Conclusion: Dehydration and electrolyte loss are not the only cause of cramping.
- http://www.ncbi.nlm.nih.gov/pubmed/15273192 This study may be most relevant or familiar as it was performed in race conditions. Experimenters took weight measurements and blood samples from ultramarathoners before and after a race, then looked for relationships between cramping and their weight and/or electrolyte concentration in the blood. Overall, there was no difference between those with and without cramps in terms of bodyweight (an indirect measure of dehydration) or electrolyte profile. Conclusion: Dehydration and electrolyte loss are not associated with cramping.
- http://www.ncbi.nlm.nih.gov/pubmed/17465609 This study summarizes a number of different data sources to try to determine what might be the cause of acute cramping, if not dehydration and electrolyte loss. The presented theory highlights spinal reflex mechanisms which are a result of localized muscle fatigue as a cause of the muscle cramps. In other words, muscle fatigue from endurance exercise leads to a neuroskeletal feedback loop that causes unwanted muscle contractions at the fatigue site. Conclusion: Cramps are brought on by muscle fatigue.
This jives with a couple of common sense arguments that I’ve always had. The first is: “Electrolyte and fluid loss are everywhere in the body, but cramps are very localized.” If these were the causes, you’d expect cramps to hit your whole body. The second is: “Cramps really only hit people in longer races.” You’d expect a decent incidence of cramping in short races from people who showed up dehydrated if this was the leading cause, but that’s not really the case.
OK, on to the typical prevention approach…drink early and often in a race. Aside from the potential issues with hyponatremia, over-hydrating also is a poor energy management strategy during a race. Consuming drinks takes energy to do (i.e. moving across the road, slowing down and speeding up, messing with breathing cadence), and digestion takes energy as well. Plus an over-full stomach is no fun to try to run hard with. So, I’m much more of an advocate of drinking only when thirsty. Same goes for managing cramps when they set in. Not only do I think it’s treating the wrong cause, but it’s going to lead to the potential for other problems (like barfing…).
Let’s flip the whole thing and approach cramps from the perspective of the last article. If cramps are caused by muscle fatigue, the only way to avoid them is to train your muscles to fatigue later and later. So, this is why I prescribe a couple of specific things for people training for marathon (or longer) races:
- As many miles as the body can handle without getting injured during training. Time on feet wins all arguments, and muscles that have lots of practice running when tired (the whole idea of mileage) become more efficient and fatigue later.
- Long runs with minimal fueling. Not every long run, but some long runs are simply time-on-feet with very little calories so that the athlete can simulate running in a depleted physical state to train their muscles how to deal with it.
When cramps do hit, and I hate to say this, there is nothing you can really do for that race. In this case, it’s all about the proper prevention strategy: Strong and well-trained legs will carry you to the finish.
Also of note: I don’t think that hydration, carbohydrate, and electrolyte consumption don’t have positive effects during training or racing, I’m just speaking of cramping in this case. And at the end of the day, we’re talking about complex and interconnected biological processes that are likely to have a number of causes. If your strategy is working for you during races, stick with it. If you’ve had cramping issues in the past, then give the extra preparation that I’ve mentioned a try.