Finding the point where weight loss hurts performance.


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.

He 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 raises some questions: What is the ideal weight for your sport? And how much difference will it make if you actually achieve it?

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 makes their performance worse, said Dr. Mark Tarnopolsky, a muscle metabolism researcher and physiologist at McMaster University in Ontario.

When he was a student, he saw the delicate balance between losing just enough and too much. He and his friends would experiment, losing or gaining weight, then 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 he got his best VO2 max ? 86 milliliters of oxygen per kilogram of body weight ? when he weighed just over 70 kilograms. “Like everyone else, I said, ‘Maybe if I drop some body fat, it will go higher,’ ” he said. So he got his weight under 69 kilograms. 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 muscle protein for fuel. He was weaker, and his performance was worse, even though he weighed less.

Often the only way to know your best weight is by trial and error.

My running coach, Tom Fleming, a former elite runner , said 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.”


By GINA KOLATA