The absolute most important thing that you can do when running in hot weather is to hydrate properly. Running in the heat is a highly taxing activity that can deplete body fluid in short order. To function at optimum levels, the body needs generous levels of fluids, mainly water. Just keep in mind the fact that a healthy human being’s body is about 60% water at any given moment, and a runner’s performance can decrease by as much as 30% with only a 2% loss of water content. By not hydrating adequately the decrease in performance is unavoidable. If dehydration is great enough, it can lead to serious injury, such as heat exhaustion, heat stroke, head trauma due to fainting, or even death.
Most people underestimate how much fluid they need to drink. While the average sedentary adult needs to drink a minimum of eight 8-ounce glasses of water per day, the average runner needs a minimum of twice that much. You should drink 16 ounces of water two hours before your run, and another 16 ounces right before you start your run.
Depending on the severity of conditions of running in hot weather, such as the temperature, your intensity, and perspiration, you should drink anywhere between four to twelve ounces of water every 20 minutes during your run. Alternatively, if you’re racing, you should be able to pick up some drink at every aid station, which are typically placed at every mile. Assuming ten minutes per mile, you would pick up a drink after every other mile. However, it never hurts me to drink at every single aid station.
After your runs, drink another 16 ounces for every 30 minutes that you ran. Not only that, you need to drink fluids throughout the day. By drinking eight ounces of fluid every 1 ˝ to 2 hours between your daily errands, you will have already done half of what is considered good hydrating. The other half will be taken care of in the moments before, during, and after your runs.
Keep in mind that if you are running in hot weather for more than one hour, replace some of the water (i.e. half the daily amount) with sports drink because the excessive perspiration will flush out needed electrolytes if you drink strictly water. Sports drinks will provide you with adequate amounts of sodium, potassium, and carbohydrates. During marathon training, my daily consumption consists of 1/3 water, 1/3 sports drink, and 1/3 fruit juices.
There are some helpful extra measures that you can take to make sure that you are properly hydrated. First, check the color of your urine. If it is yellow, or even worse, brownish, you need to drink more. It should be pale or clear. Second, even though you’re drinking lots of fluid, make sure that you are not urinating every 20-30 minutes. If you are, it means that you’re body is not retaining what you drink. This typically happens when you drink too much water, haven’t consumed enough sodium, or are consuming too many diuretics (i.e. coffee, tea, soda, alcohol). To remedy this, eat something salty such as chips, crackers, and pretzels and top it off with sports drink. Then follow up with another load every 1 ˝ to 2 hours. And don’t consume diuretics unless you have to, such as when you are on prescribed medication. Third, weigh yourself before and after your runs. For every pound that you lose after your runs, drink 32 ounces of fluid. Fourth, don’t wait until you’re thirsty to start drinking. If you are thirsty, you are already dehydrated and need to drink more.