iShape Q&A: Fitness questions answered

The SHAPE Team

Q. I do intervals on the stationary bike, pedaling for 30 seconds as hard as I can and then easing up for 30 seconds, and so on. My trainer says interval training "sets your body up to burn more fat." Is this true?

A. Yes. "It is fairly well documented that the more carbohydrate you burn during exercise, the more fat you'll burn afterward," says Glenn Gaesser, Ph.D., an exercise physiology professor at the University of Virginia and co-author of The Spark (Simon and Schuster, 2001). "Interval training burns glycogen [a form of carbohydrate stored in the liver and the muscles] at a very rapid rate."

High-intensity exercise also increases your body's secretion of growth hormone, which research has linked to increased fat-burning. Still, the extra fat-burning that comes from interval training is modest. "You might burn an extra 40-50 calories during the three to six hours after your workout," Gaesser says.

Gaesser recommends interval training two or three times a week, but not more than that. "The nature of the workout is so hard that it can lead to overtraining," he says. Remember, the best strategy for fat loss is to burn more calories than you consume, regardless of the fuel source used.

Q. I lift weights for 40 minutes three times a week. How long will it take me to gain muscle, and how much of a metabolism boost will I get?

A. "Over a 12-week period, people can increase their lean body mass by 2-4 pounds," says strength-training researcher Wayne Campbell, Ph.D., an assistant professor in the department of foods and nutrition at Purdue University in West Lafayette, Ind. However, Campbell stresses, not all of that body mass is muscle. Some may be water or other tissue. Also, men tend to gain muscle more quickly than women do.

Campbell's research suggests three months of weight training can lead to a 3- to 7-percent increase in resting metabolic rate, which translates roughly to an extra 100 calories burned per day. The exact number depends on the size of the person. Also, Campbell emphasizes, this acceleration in metabolic rate will help you lose weight only if your activity level and calorie intake remain the same. "Sometimes people offset this increase by becoming less active in other parts of the day. They go work out and then go take a nap."

To achieve these gains in lean body mass and metabolism, be sure to use heavy-enough weights. After eight to 12 repetitions, you should be unable to lift in good form and need to rest.

Q. Is it OK to run barefoot on the beach?

A. "You shouldn't run barefoot at all," says orthopedic surgeon James Maher, M.D., a clinical assistant professor at Brown University School of Medicine in Providence, R.I. "Running on soft sand is worse than running on pavement." The uneven terrain stresses your tendons as your muscles work harder to support your feet, increasing the risk for tendinitis around the ankles. "If you run on the beach, do it on hard sand and wear running shoes," Maher says.