Dehydration and Muscle Cramps

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Dehydration and Muscle Cramps While most athletes and active people realize that dehydration and electrolytes have something to do with muscle cramps, I get lots of questions like these. To find some answers, let's look at what normally happens in muscular activity using these diagrams of a single muscle cell in which K+ represents a potassium ion1 and Na+ a sodium ion, two vital electrolytes as we will see. Note that with the relaxed muscle cell there are proportionately more potassium ions inside the cell than in the fluids outside the cell while the opposite is true for sodium ions 2). When a nerve impulse is transmitted to the muscle cell, the cell membrane becomes permeable and the potassium ions can migrate out of the cell while the sodium ions can diffuse into the cell as the cell contracts. If the conditions are right, the cell will then pump the excess sodium ions out of the cell and the potassium ions back into the cell. Meanwhile, the cell is also ratcheting the muscle fibers in the cell into the stretched or so-called "relaxed" condition. The conditions are "right" when (1) there is enough water in the fluids around the cells for the ions to move freely, (2) there are enough potassium ions in this extracellular fluid to restore the "relaxed" condition, (3) there are enough sodium ions to maintain the "bridge" across the cell membrane and (4) there is enough energy available in the cell to pump the sodium and potassium ions back across the membrane and to ratchet the muscle fibers into the extended ("relaxed")3 condition. If any of these conditions are not right, the cell will not be able to stretch into the extended condition and, the next time you try to extend that muscle, it will "protest" and "refuse" to extend. If conditions in the muscles are marginal, say, you are a little dehydrated, the muscles involved will be tight and the next day they'll be sore from hundreds of "micro-muscle pulls" and the subsequent inflammation. If the conditions are worse yet or you worsen them by trying to "push" yourself even as your muscles are becoming tight, the entire muscle bundle may cramp up and you can't continue (your body's emergency "off" switch).

  • "Why do I get cramps sometimes but not others even though the workouts are the same?"
  • "Why do I get cramps an hour or more after a workout?"
  • "Why do I cramp when my teammates doing the same workout don't?"
  • "Why do I get cramps at night hours after doing anything that might have made my muscles tight, or even when I've done nothing strenuous?"

If you still try to keep going or the cramp occurs in mid-stride the muscle will probably "pull", tearing some if not all of the muscle. As you can see, it takes more than plain water to prevent or relieve muscle cramps: you also need the proper balance of electrolytes and not just a lot of salt either. For example, too much sodium will pull fluids out of circulation into the tissues, depleting blood volume and increasing stress on your heart. You don't have to be running a marathon or hiking in the desert to be dehydrated and low on electrolytes; even daily activities can leave you dehydrated and upset your electrolyte balance. Sometimes you can even have "localized" dehydration, as when you are on a long plane flight or sitting at a desk or computer and your fluids can be pooled in your legs and feet. If you get up and walk around, you can feel better because your blood is circulating more and your brain is getting rehydrated. This is also a signal that you are probably at least a little dehydrated and should replace some of that fluid. Remember that the first symptom of dehydration is diminished mental function. What about "night cramps"? Often people will wake up in the night with leg cramps even though it's been hours since they exercised or, for many people, they haven't bee exercising at all. They are dehydrated and low in electrolytes; in this case low calcium is usually the culprit and hydrating with a balanced electrolyte drink plus a calcium supplement usually solves the problem, and, believe it or not, the isotonic electrolyte drink Vitalyte won't make you get up in the night as much as plain water.


1) Ions are atoms or groups of atoms that have become electrically charged, usually when a compound is dissolved in water; for example, salt or sodium chloride (NaCl) becomes sodium ions (Na+) and chloride ions (Cl-); substances that break up in water to form these electrically charged particles are called electrolytes.

2) Why do they use these symbols instead of P for potassium and S for sodium?" These chemical symbols come from the Latin names kalium and natrium respectively; P and S were already taken for phosphorus and sulfur when potassium and sodium were discovered.

3) Note that the so-called "relaxed" term for the extended muscle is a misnomer; it has taken energy to get it extended and no energy is needed for it to contract, very much like a rubber band.

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