FREE FATTY ACIDUSE. I’ve been told that on long runs and during marathons, [should use water for the first 90 to 120 minutes to teach my body to switch over to using free fatty acids. Is that true?

Rita Hetter Seattle, Wash.

NOT REALLY. Your working muscles do not have the capacity to “learn” anything. In the many hours before your long run or your marathon, you will have been resting, hopefully taking in good nutrition, and your working muscles will havea plentiful supply of both carbohydrates and fatty acids. So will your liver. These are the tissues that will provide the energy to get you through the long run or marathon. At rest, your primary energy source is fatty acids, with some carbos as well. As you increase your activity level, you’ll significantly increase the use of both carbos and fatty acids, thereby switching the ratio from predominantly fatty acids to predominantly carbohydrates.

For marathon race pace, this is roughly 50/50 or even 60/40, with carbohydrates predominating. For a 10K race the emphasis is on almost all carbohydrates. Thus this ratio is not influenced as much by what you are drinking as by the intensity of your

September/October 1998

exercise. If you are drinking water, you will replenish the fluid you are losing as sweat. If the fluid has carbohydrates in it, some of those will absorb into the working muscles and replace what is being lost. Drinking pure water rather than energy drinks will not change your ratio of fuel usage; changing your pace will. —Dave Martin, Regents’ Professor of Health Sciences at

Georgia State University in Atlanta, is a member of this magazine’s Science Advisory Board.

I ASSUME from your question that you are a marathoner who is used to doing training runs of 90 to 120 minutes or longer. Depending on your training pace, and on your initial liver and muscle glycogen (carbohydrate) stores, you will use free fatty acids (FFA) increasingly as your liver and muscle glycogen stores decrease, which normally may take 90 to 120 minutes. If you consume carbohydrates during the early stages of the run, you may reduce the reliance on your initial glycogen stores, particularly those in the liver, and thus you may delay the gradual transition to using more FFA. Drinking water alone, as opposed to drinking a carbohydrate solution, might expedite the transition to greater FFA oxidation. However, I am not aware of any research that has studied the particular question you ask, so we do not know if the strategy of drinking only

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water, with no carbohydrates, would provide you with any advantage above and beyond the increased FFA oxidation rates you currently have developed through your long runs.

What we do know is that consuming carbohydrate solutions during marathon running will enhance performance compared to drinking water alone. As you train, your muscles learn not only to oxidize more fat, but also to oxidize more carbohydrates. That is one of the reasons training allows you to run faster, because carbohydrate is the primary muscle fuel for higher-intensity exercise. It might actually be to your advantage to practice taking carbohydrates during your training runs, to mimic that which you willdoin marathon competition. Consuming up to 60 grams of carbohydrate per hour (about a quart of a six to seven percent glucose-electrolyte solution over the course of the hour) approximates the maximum amount of ingested carbohydrate the body can oxidate when running.

Practicing carbohydrate intake during training may get your body used to using this strategy, one that has been shown by research to effectively prevent premature fatigue during prolonged running.

—Mel Williams,

professor emeritus in the Department of Exercise Science at Old Dominion University in Norfolk, Virginia, is on the M&B Science Advisory Board.

I’M NOT sure you can “teach” your body to do anything of the sort. When your body finishes using all of the carbohydrate fuel available, it will

start dipping into fat stores. You are liable to be “running on empty” soon. You should keep your glycogen (or carbohydrate) level up as long as possible, whichis why you carbo-load before a marathon. The reason you shouldn’t start out too fast in a marathon is because you will burn your glycogen stores more quickly. (Glycogen is one of your body’s main carbohydrate sources for running.) As far as using water, you should take in water at every water station (or every two to three miles), along with any carbohydrate drink your body can tolerate. Remember: when you feel thirsty, it’s too late. —Lionel Haywood

is arunner and retired biology teacher living in Auburn, Washington.

MY EXPERIENCE has been that you can best avoid dehydration during long runs by drinking early. It is best to start hydrating a day or two before areal long run, especially ifitis going to be run in hot or humid weather. The only risk comes in a race where you are forced to line up 30 or more minutes before it starts. If you are too hydrated, you may have to empty your bladder after you are already on the starting line. —Mike Tymn is a many-time masters road racing

champion who lives in Hawaii and works for the Honolulu Advertiser.

Send your questions to

“On the Mark” Marathon & Beyond

September/October 1998