Do you get muscle cramps when you exercise? The combination of warmer weather and increased physical activity during the summer months raises the risk of experiencing muscle cramps. These cramps are commonly referred to as heat cramps or exercise-induced cramps. Regardless of their name, this involuntary muscle cramping can be severely painful. It occurs primarily in arms, legs and abdomen muscles. These cramps are most common in people who are just starting an exercise program or taking on new types of activity.

Question: What is the difference between heat cramps and exertional cramping?

Answer: The primary difference between these two types of cramping is body temperature. As the name indicates, the cramping is related to elevated body temperature in heat cramps. But increased body temperature is not the only thing that appears to trigger cramps, thus the name exertional or exercise-induced cramping.

Q: Who is at risk for heat/exercise-related cramps?

A: There are a number of factors that increase cramping risk, including level of training, not being accustomed to exercising in hot conditions, excess water loss due to sweating, exercising multiple times a day without adequate time to rehydrate, muscle fatigue, excess clothing and not realizing the extent of water loss when sweat evaporates quickly in breezy weather (and tradewinds).

Q: What nutritional problems cause these cramps?

A: It is rather clear there is no single reason for muscle cramps that occur during or after exercise. Some of the more common reasons suggested by researchers include general dehydration due to inadequate fluid intake and/or excessive sweat loss, excessive loss of sodium in sweat, and potentially the loss of other electrolytes in sweat. No matter what the cause, it is clear that cramping muscles are not getting adequate nutrients needed to function normally or possibly not getting the right balance or concentration of nutrients like sodium. It also is important to point out that excessive hydration without adequate salt intake can cause a condition called hyponatremia (low blood sodium) that can be deadly.

Q: What can be done to prevent cramping during or after exercise?

A: Goldilocks’ principle of finding the “just right” amount of hydration along with adequate salt intake is important to prevent cramping. Because everyone’s hydration needs are different due to variations in body size, diet and sweat loss, determining a personal sweat loss may be necessary to find your “just right” hydration strategy.

To determine personal hydration needs, measure your nude body weight before and after an hour of your typical workout.

The weight lost is essentially equal to the amount of body water lost. A 2-pound loss is equivalent to about a quart of water depleted (a kilogram or 2.2 pounds equals a liter of fluid loss).

To get your actual sweat rate, add the amount of any fluid consumed during the workout to your final loss tally. This provides a frame of reference for how much to drink during long bouts of exercise.

Alan Titchenal, Ph.D., C.N.S., and Joannie Dobbs, Ph.D., C.N.S., are nutritionists in the Department of Human Nutrition, Food and Animal Sciences, College of Tropical Agriculture and Human Resources, University of Hawaii-Manoa. Dobbs also works with University Health Services.