It’s been hot & humid out there these past few days, which has reminded me to discuss dehydration with my patients.  Dehydration occurs often when people exercise and do not properly prepare for either the intensity of their workout or the weather conditions.  Humidity can worsen the effects of dehydration and cause heat illness.  You end up sweating more and cooling less.  When you are weight training or playing your favorite sport it is very important to maintain proper hydration.  If you are thirsty, you are already dehydrated.  When you are dehydrated, your body will lose coordination, timing and performance.

Recognizing symptoms of heat injury:  There are three stages to heat illness; heat cramps, heat exhaustion, and heat stroke -- listed in order of increasing severity.  Heat cramps are due to muscle spasms and often occur in the arms, legs, or abdomen. Heat cramps are caused by dehydration and loss of salt and other electrolytes.  Heat exhaustion is due to more profound loss of water and electrolytes. It is characterized by generalized weakness, headache, dizziness, low blood pressure, elevated pulse, and temperature elevation as high as 104° F.  Moving out of the sun, drinking fluids, and eating salty food can usually treat both.  Heatstroke is a life threatening condition and represents severe dehydration, high body temperature, and a shut-down of the cooling mechanisms.  Heatstroke may cause delirium or coma and typically has stopped sweating.  The pulse is rapid and weak, the blood pressure is low and body temperature is greater than 105°F.  Damage to the brain, heart, lungs, kidneys and other organs may occur.  This is an emergency situation.  Call 911and use ice to cool the body.

Hyper-hydrate:  Two to three hours before working out you should drink approximately 20 ounces of cold water or an electrolyte solution.  The maximum rate of fluid absorption by the gastrointestinal (GI) tract during exercise is approximately 27 fluid ounces/hr.  The rate of fluid loss through sweating may average as high as 50 - 68 fluid ounces per hour. So despite the best fluid intake, dehydration will occur.  Drinking 5 - 8 ounces every 10 - 15 minutes is probably the best way to attempt to stay hydrated while running or exercising intensely.  Also, the more dehydrated you get the harder it is for your GI system to absorb what you drink. Dehydration can also cause a variety of GI symptoms (nausea, cramping, and diarrhea).  Most sports drinks have a  sodium content in the range of 10 - 20 mmol/liter (Gatorade is 23 mmol/liter = 1.3 grams of salt per liter). Higher levels are better for salt replacement.  There doesn't appear to be any advantage gained from adding other electrolytes (e.g.. potassium, magnesium) since the diet is usually adequate to replace these.

Overall, quite simply, when it is hot and humid outside, drink water or a sports drink a few hours before you plan to workout.  This should prevent dehydration and heat illness and allow your body to perform at its best.