Recently a client reported a severe cramp in a calf during consecutive runs.  The first cramping occurred while trying to do an all-out six minute run (it is a field test I do with runners); the next day during an easy run he cramped in the same calf.  He noted that he was well-hydrated for the first run and ran with a Cameback the next day.

Well, it inspired me to write about cramping.  Contrary to folklore (and what I was taught) cramping during exercise is not a result of dehydration or electrolyte loss.  Cramping is a neuromuscular issue.  I will make the case for this new theory, but first let's take a look at the traditional view of cramping.  

First, let's define a cramp as a painful, spasmodic, involuntary contraction of skeletal muscle during or immediately after exercise.  It is critical to note that this discussion will be limited to cramping as a result of exercise; cramps under other conditions may (are?) different.

One difficulty in studying cramping is that there is not a way to control and initiate cramping in the lab.  No one has a "cramp inducer" that can be hooked up to a person and a cramp be created.  This makes it very challenging to study.

Electrolyte/Dehdyration Theory

This theory proposed that cramps are caused when electrolyte concentration in the body is reduced.  However, when you sweat, as you would do during intense exercise or even moderate exercise under hot conditions, you lose electrolytes such as sodium, but you also lose a lot more water;  thus the loss of water with a small amount of electrolytes would lead to an INCREASE the concentration of electrolytes in the body.  

Another problem with this theory is that you are going to lose electrolytes throughout your body during exercise so why doesn't your entire body cramp?  Cramps tend to occur overwhelmingly in the muscles being used for exercise.  As a runner you may cramp in your leg while running, but how often do you cramp in your arms while running?

Here are a few studies to support the above claim that low sodium (or other electrolytes) are not the cause of cramps.

British Journal of Sports Medicine

Medicine in Sport Science and Exercise

Sports Medicine

A Modern Theory

In the late 90s, Martin Schwellnus proposed a new theory: muscle cramps are a result of as sustained and dysfunctional reflex control of the motor neuron due to fatigue.  Basically, a cramp was occurring when the electrical signal going to the muscle is increased and contraction occurs.

Skeletal muscle has two small organelles inside the muscle cell (fiber) that help to protect it from damage.  The muscle spindle is located on the "belly" or thickest part of the muscle fiber and is sensitive to stretch.  When the spindle senses that the muscle is being stretched past its safe length, a signal is sent to the spinal column and the spine reflex causes the muscle fiber to contract (shorten).  So if you stretch a muscle at some length the muscle senses it is in danger and will contract to protect itself.  The second organelle is the Golgi Tendon Organ (GTO) that is located along the tendon connecting the muscle to the bone; the GTO is sensitive to force or loading.  If the GTO senses that the load on the muscle is too great and could cause damage, the GTO will also send a signal to the spinal column and activity in the GTO is decreased.  Both are designed to protect us from hurting ourselves although the system does fail.

Schwellnus' theory is that net change in muscle spindle and GTO activity leads to a condition where the muscle contracts involuntarily and does not relax. It has been shown that when a muscle fatigues, muscle spindle activity increases; when a muscle fatigues GTO activity decreases.  When a muscle is active, it is likely to fatigue.  Muscles that cross two joints are also more likely to cramp--think of the calf in swimming where toes are pointed and the muscle is contracting in a shortened position.

Most of the time cramps occur in racing when exertion levels are high and fatigue is at its greatest, but it can occur when doing a near maximal effort (as I was asking my client to do).  


First, although dehydration and electrolytes depletion are not causes of cramping, that does not mean that hydration is not important.

Regular stretching should help reduce the risk of cramping during exercise. If you are exercising and develop a cramp, stop and stretch. This will often make the cramp go away.  Actually this is a really good example of why the dehydration/electrolyte model does not explain cramping.  If it was about fluid or sodium then why would stretching help?

What about electrolyte pills or pickle juice?  First, in some cases if you do nothing a cramp will go away so be wary of "cures".  Second, if these interventions world for you then do them!  Cramping is complex.  Third, there is the possibility that pickle juice might relieve cramps by sending a signal to the brain that signals the relaxation of the contracted muscle.  For more information here is the abstract to the study and also a New York Times write up.


  1. Keep hydrating as water is critical for many bodily functions.
  2. Hydration is not likely to stop cramping.
  3. Stretch regularly to reduce the risk of cramping.
  4. If you are cramping, pickle juice or vinegar may relieve the cramp faster than doing nothing.
  5. Bananas are not going to help although they are nutritious and delicious.