Runner's CornerAugust 2007 :: Index of issuesAvoiding Dehydration: How to Hydrate Properly August 2007 Runner’s Corner By Kitty A. Consolo, Ph.D. With the dog days of August upon us, many of us find ourselves training in high heat and humidity. Our biggest enemy becomes dehydration. This month’s runner’s corner will address ways to determine if you are dehydrated and how to determine how much water you need without getting too much. The amount of water we need per day depends on our weight and activity level. Body-water balance is maintained when the amount of water and body fluids that leave the body is matched by the input of water. If the output exceeds the input as can be during heavy exercise particularly in a hot environment, then dehydration will occur. Of particular concern to the distance runner is the effect of dehydration on performance. Dehydration can lead to deterioration in aerobic performance due to adverse effects on cardiovascular functions such as a reduction in cardiac output which increases systemic and cutaneous vascular resistance during exercise. Dehydration may also be a major factor in gastrointestinal distress. Checking for Physiological Warning Signs of Dehydration One way to tell if you are dehyrated is to pay attention to urine color. If one’s urine becomes a dark yellow or orange color, dehydration is likely. Urine color is biomarker that can be useful in assessing dehydration status however, keep in mind other variables can affect urine color besides hydration status such as the intake of vitamins, foods, such as beets and medications. Signs of Dehydration and Heat Illness One should also know the following signs of dehydration and heat illness such as disorientation, irrational or unusual behavior, irritability, headache, nausea, loss of balance and muscle function, dizziness, confusion, profound fatigue, hyperventilation, diarrhea, delirium, seizure or coma. Recognizing some of the earlier signs such as headache, nausea and disorientation can lead to early treatment and the prevention of the more serious symptoms of heat illness such as seizure or coma. Drinking According to One’s Sweat Rate Another useful tool in preventing dehydration is to measure ones sweat. Sweat rate determinations also can help avoid hyponatremia, a serious medical condition in which sodium levels in the blood become too low. Most cases of hyponatrmia have been reported in marathons, but victims have often been small, inexperienced female runners who drank too much water (Williams, 2007). To accurately use the formula below, be sure to have an accurate scale, calculators and plastic measuring cups. Sweat Rate Formula (Williams, 2007; Nieman, 2003)
This final number is the approximate number of ounces you need to consume per hour to stay hydrated. (Note: If any urine is lost, this should be measured too and added back in, but most runners can go through a practice without having to urinate and some athletes may be adverse to measuring urine, so measuring sweat rate without this step is usually preferred). On race day, bring your own water bottle with enough water to match your pre-calculated sweat rate. Drink cool water prior immediately prior to the race based on your sweat rate (Williams, 2007) and then drink enough water after the race to make up for weight lost during the race. Summary Using urine color and calculating your own sweat rate can help you maintain adequate hydration status which will not only prevent heat injury and illness, but less detrimental effects of the heat on your running performance. Just a 1% loss of body weight due to dehydration can significantly decrease running performance. Knowing your sweat rate also reduces the likelihood of consuming too much water and developing hyponatremia. Hope to see you running well at the race. |