Calf Cramps Strike Again!

Sports Doc helps a runner who suffers from mid-race muscle cramps.

Kyle asks: Every time I run a marathon, I get bad calf cramps at kilometre 32. I carb up the week before and also eat a good amount of protein. I’m very hydrated before the race and take in fluids and gels during the race. I just don’t know what to do. Maybe my training needs to change. I just wondered what advice you could give?

Exercise-associated muscle cramps occur in many marathon runners during and immediately following the race. You have asked a question that is embroiled in controversy, with cramps due to dehydration and electrolyte imbalance versus cramps due to neuromuscular dysfunction and fatigue camps on opposite poles of the argument. The differences of opinion lead to heated debates at exercise-medicine conferences and in the sports-related literature.

My personal view from being at the finish line and sideline of many running events is that most cramping is due to muscle fatigue and nerve-mediated contractions. It is rare for cramps to occur from dehydration; you’d need to sweat large volumes of water and salt.

It sounds as if you are both well-nourished and well-hydrated during runs, so the dehydration and electrolyte imbalance model seems unlikely. Unless you feel thirsty, I would not recommend increasing your fluids during your training or racing. Near the end of the race, you may have reached the fatigue limit of your calf muscles at your current pace.

At some point in continuous activity, the excitatory stimulus overwhelms the inhibition from the Golgi tendon and alters the neuromuscular control at the spinal level, which results in cramps. Stretching the muscle group restores muscle inhibition and relieves the cramp. The physical therapists at the Medtronic Twin Cities Marathon apply this technique and relieve most of the cramps that come through our medical tent. Sometimes this does not work and we use a bolus of intravenous normal saline fluid to relieve the cramping, and in rare cases, we use midazolam (a benzodiazepine) to chemically relieve the cramps.

In most marathon training programs, 32 kilometres is the longest distance run because pushing beyond this distance increases the risk of injury. It may be that you will need to increase the long run distance or make some other adjustment to your training program to avoid muscle fatigue at kilometre 32. It may also be that your limit is 32km.

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