By GINA KOLATA
IN his new book, “Racing Weight: How to Get Lean for Peak Performance,” Matt Fitzgerald, a sports nutritionist, writes about an amazing running experience. He worked out on a special sort of anti-gravity treadmill, the AlterG, which uses a cushion of air to lift the body, allowing you to effectively decrease your body weight as you run.
Mr. Fitzgerald started out on the treadmill by running without the machine’s assistance. Then he ran with it adjusted to lift him just enough so that he was 10 percent lighter.
“I felt as if I had become 10 percent fitter,” he writes. Running at his usual pace was suddenly “utterly effortless,” he notes, adding that “it felt like normal running, only so much better.”
Exercise physiologists agree that if your sport is particularly affected by the tug of gravity — running, cross-country skiing, cycling up hills — you are penalized for excess weight. But that leaves some questions: What is the ideal weight for your sport? And how much difference will it make if you actually achieve it?
There have been few direct tests of the body-weight effect, said Hirofumi Tanaka, an exercise physiologist at the University of Texas at Austin. Most of them were done in the 1970s and involved subjects who were asked to run with weights on their backs or ankles. Sure enough, the heavier the people were, the tests showed, the harder they had to work to run at a given speed.
But the runners’ forms were not affected by the extra weight, Dr. Tanaka said. That means that you would probably run the same way if you were heavier. But it would be a lot harder to run at your usual pace, and you’d end up running more slowly.
How much is less clear. Beth Parker, the director of exercise physiology research at Hartford Hospital in Connecticut, said that, for runners, the general rule is that a 1 percent reduction in weight leads to a 1 percent increase in performance.
So, why not just be as thin as you can be?
The problem is that everyone has a point at which further weight loss actually makes their performance worse, said Dr. Mark Tarnopolsky, a muscle metabolism researcher and physiologist at McMaster University in Ontario. Dr. Tarnopolsky, who is a nationally ranked athlete in winter triathlons, adventure racing and ski orienteering, said that people vary so much that there is no formula to figure out the perfect weight.
When Dr. Tarnopolsky was in graduate school, he saw the delicate balance between losing just enough and too much. He and his friends would experiment, losing or gaining a few pounds and testing their VO2 maxes, a measure of the body’s ability to get oxygen to muscles during exercise. In theory, the less you weigh, the higher your VO2 max should be, relative to body weight.
Dr. Tarnopolsky said that he got his best VO2 max — 86 milliliters of oxygen per kilogram of body weight — when he weighed 156 pounds. “Like everyone else, I said, ‘Maybe if I drop some body fat, it will go higher,’ ” Dr. Tarnopolsky said. So he got his weight down to 152 pounds. But to his surprise, his VO2 max decreased, to 82.
The likely reason, he said, was that he had reached a point where his body began burning its own muscle protein for fuel. He was weaker, and his performance was worse, even though he weighed less.
“You could see on the VO2 machine what your body knew was right,” Dr. Tarnopolsky said. “You’d feel tired, stale, lethargic when you tried to drive your weight down.”
Often the only way to know your best weight is by trial and error.
My running coach, Tom Fleming, a former elite runner who won the New York City Marathon twice, in 1973 and 1975, said that he always tells his competitive athletes “that the perfect weight is the weight you are the day you P.B. in your event,” referring to the time you achieve your personal best — or fastest — finish.
“Your body will tell you” your perfect weight, he said, and when you are there, “you will feel fast, race fast.”
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