Runners have many questions about how to fuel for top performance. The Internet abounds with answers—but how do you what’s valid? Here are some trust-worthy answers, based on research presented at the American College of Sports Medicine’s Annual Meeting (www.ACSM.org).
HYDRATION
When training in heat, what’s best to drink?
In a simulated heat wave study, trained athletes exercised lightly for 3 hours in each of 4 trials. They drank either 1) room temp water (68° F/20° C) as desired, 2) cold water (40° F/4° C) as desired, 3) no fluid replacement, or 4) full replacement of sweat losses with programmed drinking. Obviously, those who drink nothing suffered the most heat strain. Those who drank ad libitum (as desired) consumed enough to prevent dangerous levels of dehydration. The athletes drank more of the room-temperature water. Preliminary findings suggest the cold water blunted thirst. Be careful about how much ice you put in your water bottle?
I’m afraid of becoming dehydrated during a marathon. I plan to push fluids. How much is too much to drink?
While drinking an extra-large volume of fluid before endurance exercise might seem advantageous, the question arises: would doing so actually trigger a diuretic effect and, thus, not provide the desired benefit (hyper-hydration). To test that theory, subjects drank 5, 10, 15 or 20 ml/kg of a sodium-containing beverage. That’s about 12 to 50 ounces (350 ml to 1,400 ml) for a 155-lb (70 kg) person. The data suggest the athletes retained about half of what they drank, regardless of the volume consumed. Thus, if you will be exercising in the heat, tank up as tolerated.
How much harder do you need to work when exercising in the heat at altitude?
In order to meet the combined demands of increased blood flow to the skin (to dissipate body heat) plus transport of adequate oxygen to the exercising muscles, the heart has to work about 17% harder than at sea level during 30 min of moderate intensity exercise. If you are a fit, healthy person who is just running at altitude or just running in the heat, the heart works about 10% harder. No wonder exercising at altitude and/or in the heat is tiring! Programmed eating and drinking can help provide the extra energy and fluids needed to support the extra effort.