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Archive for March, 2015

Why do we get muscle cramps while exercising?

The answer to this question is quite simply…… we still don’t know. Most people, even trainers, think that it is due to the loss of salts or electrolytes but in the past few years the scientific evidence out there clearly does not support this hypothesis. But most people still believe this thanks, in part, to the help of sports drinks.

This myth started almost 100 years ago in shipyards and mines, where workers were cramping up.  They did an analysis of their sweat which showed that it contained high levels of chloride (an electrolyte). So, they came to the conclusion that loss of electrolytes was the reason for the workers’ muscle cramping, along with dehydration. The problem with this is that they never checked the sweat of the people that were not cramping up. So, it sounded logical but this hypothesis had a couple of weak links.

  1. The first one being: When we sweat, we tend to sweat all over our body, meaning we are losing electrolytes equally in all  parts of our body. But somewhat surprisingly, exercise-associated muscle cramps only happen in the muscles that have been used extensively for the exercise. Kind of weird, right?
  2. When we sweat we lose much more water than electrolytes. In fact the loss of electrolytes is very low. Meaning that the concentration of electrolytes in our body is actually going to be higher than before doing the sport or activity. Also, two studies done on  ultramarathoners , showed that the runners who cramped up had a significantly lower sodium concentration (this means these runners were over-hydrated ), and lost less weight, and the more direct measures of the fluid in their blood showed they were better hydrated (1-4).  Amazing, isn’t it?
  3. Whenever we cramp up, we stretch and that usually makes the cramp go away for a while. So, if cramping is caused by loss of electrolytes or dehydration, how can simply stretching the muscle help us getting rid of our cramp?

Then why do we cramp up while exercising? Well, there is a new theory out there that basically says we cramp up because of fatigue. Let me explain: Muscle contraction is stimulated by a nerve, called the alpha motor neuron. One of the places this neuron gets its information from is muscle spindles and the golgi tendon organ.

1) Muscle spindles- We have probably all experienced the classic reflex, where a doctor or friend taps on the knee with a small hammer and you extend the leg. So, whenever your muscle is stretched too much, the muscle spindles activate and produce a muscle contraction (5).

2) Golgi tendon organ- Does the opposite, when it feels that a muscle is contracting too much, it will send a signal telling the muscle to relax (5).

Fatigue has been shown to increase the rate of muscle spindle and decrease the rate golgi tendon organ (5). Most muscle exercise cramps happen at the end of a race.

I will leave it at here for today. In my next blog I will talk about what we can do to try to prevent muscle cramps.




  1.  Schwellnus, M.P, Nicol R, Laubscher R, Noakes T.D Serum electrolyte concentrations and hydration status are not associated with exercise associate muscle crampint (EAMC) in distance runners. Brit J Sports Med 38(4): 488-92.
  2. Miller K, Knight K, Mack G, et al. Three percent hypohydration does not affect the threshold frequency of electrically-induced muscle cramps. Med Sci Sports Exerc. 2010;42:2056-2063.
  3. . Braulick K, Miller K, Albrecht J, Tucker J, Deal J. Significant and serious dehydration does not affect skeletal muscle cramp threshold frequency. Br J Sports Med. 2012;47:710-714.
  4. Sulzer N.U, Schwellnus M.P, Noakes T.D. Serum electrolytes in Itronman triathletes with exercise-associated muscle cramping. Med Sci Sports Exerc 3(7): 1081-85.
  5. Schwellnus M.P, Derman E. W, Noakes T.D. Aetiology of skeletal muscle cramps during exercise: A novel hypothesis. Journal of Sports Sciences, vol 15, pp 277-85, 1997.

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