Activity: Authorities recommend stretching before and after exercise or sports, along with an adequate warm-up and cooldown, to prevent cramps that are caused by vigorous physical activity. Good hydration before, during, and after the activity is important, especially if the duration exceeds one hour, and replacement of lost electrolytes (especially sodium and potassium, which are major components of perspiration) can also be helpful. Excessive fatigue, especially in warm weather, should be avoided.

How much should I drink?

Hydration guidelines should be individualized for each person. The goal is to prevent excessive weight loss (>2% of body weight). You should weigh yourself before and after exercise to see how much fluid you lose through sweat. One liter of water weighs 2.25 pounds. Depending on the amount of exercise, temperature and humidity, body weight, and other factors, you can lose anywhere from approximately .4 to 1.8 liters per hour.

Pre-exercise hydration (if needed):

1. 0.5 liters per hour for a 180-pound person several hours (three to four hours) prior to exercise.
2. Consuming beverages with sodium and/or small amounts of salted snacks or sodium-containing foods at meals will help to stimulate thirst and retain the consumed fluids.

During exercise:

1. Suggested starting points for marathon runners are 0.4 to 0.8 liters per hour, but again, this should be individualized based on body weight loss.
2. There should be no more than 10% carbohydrate in the beverage, and 7% has generally been considered close to optimal. Carbohydrate consumption is generally recommended only after one hour of exertion.
3. Electrolyte repletion (sodium and potassium) can help sustain electrolyte balance during exercise. 

Under these conditions, adding modest amounts of salt (0.3 g/L to 0.7 g/L) can offset salt loss in sweat and minimize medical events associated with electrolyte imbalances (for example, muscle cramps, hyponatremia).

Post-exercise:

1. Drink approximately 0.5 liters of water for every pound of body weight lost.
2. Consuming beverages and snacks with sodium will help expedite rapid and complete recovery by stimulating thirst and fluid retention.

Pregnancy: Supplemental calcium and magnesium have each been shown to help prevent cramps associated with pregnancy. An adequate intake of both of these minerals during pregnancy is important for this and other reasons, but supervision by a qualified health-care practitioner is essential.

Dystonic cramps: Cramps that are induced by repetitive non-vigorous activities can sometimes be prevented or minimized by careful attention to ergonomic factors such as wrist supports, avoiding high heels, adjusting chair position, activity breaks, and using comfortable positions and equipment while performing the activity. Learning to avoid excessive tension while executing problem activities can help. 

Rest cramps: Night cramps and other rest cramps can often be prevented by regular stretching exercises, particularly if done before going to bed. Even the simple calf-stretching maneuver, if held for 10 to 15 seconds and repeated two or three times just before going to bed, can be a great help in preventing nocturnal cramps. The maneuver can be repeated each time you get up to go to the bathroom during the night and also once or twice during the day.

Another important aspect of prevention of night cramps is adequate calcium and magnesium. Calcium intake of at least 1 gram daily is reasonable, and 1.5 grams may be appropriate, particularly for women with or at risk for osteoporosis. An extra dose of calcium at bedtime may help prevent cramps.

Supplemental magnesium may be very beneficial for some, particularly if the person has a magnesium deficiency. However, added magnesium can be very hazardous for people who have difficulty eliminating magnesium, as happens with kidney insufficiency. The vigorous use of diuretics usually increases magnesium loss, and high levels of calcium intake (and therefore of calcium excretion) tend to increase magnesium excretion. A supplemental dose of 50-100 milligrams of magnesium daily may be appropriate. Splitting the dose and taking a portion several times during the day minimizes the tendency to diarrhea that magnesium can cause.

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