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Exercise associated muscle cramping

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Exercise associated muscle cramping (EAMC), is an interesting phenomena that most endurance athletes will have suffered from at one time or another. It is important that we differentiate between EAMC and none EAMC. In this article only EAMC will be focused on and from here on EAMC will be referred to simply as cramp.

Dehydration and electrolyte imbalances are often thought to be the cause of cramping. However there is little association between them. Now I do not want you to take my word for this as I know a lot of people would be quick to say otherwise. So let’s have a closer look at the evidence. Researchers from Cape Town in South Africa have done numerous studies looking at cramping. One large cohort study that will be relevant to many readers is that of Schwellnus et al (2010). In this study 210 Ironman triathletes who were competing in the South African Ironman were recruited. These athletes were grouped into either a ‘cramp’ or ‘no cramp’ group, depending on whether they experienced cramping episodes during the race. The athletes were weighted and had a blood sample pre and post race along with some questioning about their background and training.

Body weight change during exercise is an easy way to indirectly measure fluid loss. It can be assumed that apart from a small about of weight loss from substrate usage, the majority of body weight change during exercise is due to fluid loss through sweat and respiration. Using this method it was found that following the Ironman race both the group who experienced cramps and those who did not experience cramp had similar changes in body weight (~2.3 kg) and therefore fluid loss. This similar fluid loss over the race in both groups indicates that hydration was not a factor in causing the cramps that those in the cramping group experienced.

It is commonly thought that electrolyte balance plays an important role in cramp prevention. However, when plasma sodium, potassium and chloride were analysed pre and post race there were no differences between the group that cramped and the group that did not. So with dehydration and electrolyte imbalances not causing the cramp what could it be? In this study by Schwellnus et al (2010) of Ironman competitors the two factors that were related to cramping were previous cramping episodes (i.e. if you have cramped before you are more likely to cramp again) and finishing time (the faster you go the more likely you are to cramp). However, that is not very useful for us.

In some studies that measured muscle activity it seems likely that cramp is related to neuromuscular factors (Sulzer et al, 2005). In other words the link between the brain and the muscle is being disrupted somewhere causing the muscle contraction to be interrupted causing a cramp. Some very recent research presented at the 2011 European College of Sport Science conference also by Schwellnus indicates that there may in fact be a specific gene responsible for cramping that some people are predisposed to (so you may be able to blame your parents while you hobble to the finish line in your next race).

While the exact mechanisms of cramps are still unknown the information that we do have can provide some insightful information into potentially helping us prevent and deal with cramps. Because cramps are potentially a neuromuscular problem there needs to be a focus on training the neuromuscular system to deal with the rigors of race day. If there is a miss-match between training and racing intensity, duration or specificity it will increase the potential for the neuromuscular system to cramp.

The Speights Coast to Coast mountain run is a classic example of this, with many individuals cramping towards the end of the run. While most have done practice runs over the course to get the required duration and specificity most will not run at their race intensity during their training for the full duration. So when the muscles are asked to contract and relax again and again at an intensity they are not use to, there is a breakdown in communication in the neuromuscular system resulting in cramps.

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Another example of this was in 2010 when the Coast to Coast Longest day competitors arrived at the Atkins transition only to be told that they had to run over Arthurs Pass via the road instead of the normal route off road over Goat Pass. Now while it is only anecdotal evidence there seemed to be a large number of athletes experience cramp in the first part of the run that year. All of them were fit, had trained hard specifically thinking their race was going to be held over rocks. However, when they were required to run over the road the neuromuscular pattern required was quite different. The mismatch between training and racing requirements lead to cramping.

So that is all very good, but what can you do when you are in the middle of a race and the cramp starts to bite? There is some research that indicates static stretching can help relieve cramp, however whether it is the stopping to stretch or the stretching itself that relieves that cramp is a grey area. I think the most important thing to remember is that cramp is signal from your body that you are working beyond your means and that you need to slow down otherwise your body will make you slow down.

Now that we know that cramp is not related to dehydration or electrolyte imbalances the best advice I can offer is, listen to your body. If you are starting to cramp slow down. Sure you will not be going as fast but if you keep going at the intensity you were you will soon get full blown cramps. Going a little slower now is faster than lying on the side of the road/ track because your cramps have gotten so bad.

If you have any questions about cramp or topics you would like to read about in future articles please feel free to get in touch with me.


1)SChwellnus, M.P, Drew, N & Collins, M. Increased running speed and previous cramps rather than dehydration or serum sodium changes predict exercise-associated muscle cramping: a prospective cohort study in 210 Ironman triathletes. In: Br J Sports Med, 4: 650 – 656, 2010

2)Sulzer, N.U, Schwellnus, M.P & Nokes, T.D. Serum Electrolyte in Ironman Triathletes with Exercise-Associated Muscle Cramping. In: Med & Sci in Sport and Exercise, 37: 1081 – 1085. 2005

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