Cramping and Dehydration in Athletes

Water is a critical component of our body’s survival. Adequate hydration is essential to allow the body to function properly. Up to 70-75% of our body’s weight is made up of water. Most of this water is located within the cells of our body. The remainder is found in the extracellular space, which consists of the blood vessels and the space between our cells.

Dehydration occurs when the amount of water leaving the body is greater than the amount being absorbed. Our bodies are dynamic and always changing so be aware of the activity you are doing at the time. This is true with water in the body. We lose water easily when we:

  • breathe and humidified air leaves the body
  • sweat to cool the body; and
  • Eliminating waste by urinating or having a bowel movement.
  • Also water is consumed by the body in just its day to day functioning of our organs

Athletes (and everybody else) need to consume a significant amount of water to replace this regular loss.

All Sports and other vigorous activities can cause excessive fluid loss from perspiration. This kind of dehydration increases the likelihood of muscle spasm and cramps. These cramps are more likely to occur in warmer climates and can be an early sign of heat stroke.

Chronic depletion of body fluids from diuretics (be careful as diuretics can also be found in shakes that contain large amounts of caffeine) and poor fluid intake may act similarly to predispose the athlete to cramps. Sodium depletion has also been associated with cramps. Loss of sodium, the most abundant chemical constituent of body fluids outside the cell can also attribute to dehydration.

Low blood levels of either calcium or magnesium directly increase the excitability of both the nerve endings and the muscles they stimulate. This may be a predisposing factor for the spontaneous cramping experienced by some athletes. Cramps are seen in any circumstance that decreases the availability of calcium or magnesium in body fluids, such as taking diuretics, (as mentioned above), over breathing, excessive vomiting, inadequate calcium and/or magnesium in the diet, and inadequate calcium absorption due to a vitamin “D” deficiency. This in turn can see a poor function of the parathyroid glands (tiny glands in the neck that regulate calcium balance), and other conditions.

Low potassium levels can occasionally cause muscle cramps, although it is more common for low potassium to be associated with a weakness in the muscle itself.

The calculation below can assist you in determining your water requirements. Also ensure you or your athlete has good electrolyte replacement, and by this I mean a good electrolyte purchased from your pharmacy, not sugary drinks claiming they are good for electrolyte replacement at the local café or food store. Most of these are full of sugar, preservatives and additives that are not good for us.

Hydration requirements:

For the first 10kg of body weight the daily fluid intake required is 100cc per kg. For the next 10kg of body weight, the fluid required is an additional 50 cc/kg.


John Hart

“Master’s In Education” (Disability) Newcastle University Australia

“Grad Cert Education” Newcastle University Australia

“Diploma Fitness/Recreation”

“Diploma of Sport and Recreation”

“Cert 4 Personal Training”

“Level 1 Strength and Conditioning Coach”

Member of ASCA (Australian Strength and Conditioning Association)

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