Q&A: The best way to train abs. And post-workout calorie burn

Q. I know that the old-fashioned sit-up is considered obsolete because it engages the hip flexors. But why is that such a bad thing if it's also strengthening the abs? On the recommendation of an ex-Marine, I added sit-ups to my workout and find them very challenging. I can easily do 300 crunches, but I have a tough time doing 50 full sit-ups. Why are we being taught to avoid them?

A. "Full sit-ups are just wasted effort," says Palm Springs, Calif., trainer Scott Cole, co-creator of the Best Abs on Earth video. "You're only working your abs in the first 30 percent of the movement." If you can perform 300 crunches, you're probably crunching too quickly, relying on momentum rather than muscle power. Or perhaps you're using your arms to fling your neck forward rather than lifting from your torso. "You should be able to isolate your abs in 20 crunches or less," he says.

Crunches are a better use of your time than sit-ups, Cole says, but even when performed properly, they're not the most effective way to train your abs. In real life, your abs work with other muscles -- your back and gluteal muscles -- to stabilize your spine. So it makes more sense to train them in conjunction with these muscles than to isolate them with a movement, such as the crunch, that is foreign to daily life or sports. "Crunches don't allow your abs to lengthen fully," Cole says. "If you watch Marion Jones sprinting, you'll see her abs lengthening and contracting as they stabilize her torso. Athletes don't do 800 crunches or have Ab Rollers. The people who have great abs take a multidimensional approach." Cole suggests tai chi, kickboxing or a power-yoga class (see "Power Up Your Yoga" on page 136) that emphasizes core-focused exercises.

Q. Is it true that your body continues to burn extra calories for 12 hours after you've worked out?

A. Yes. "After vigorous exercise, we've seen caloric expenditure increase for up to 48 hours," says exercise physiologist Tom R. Thomas, Ph.D., director of the exercise physiology program at the University of Missouri in Columbia. The longer and harder you work out, the greater the post-workout metabolism increase and the longer it lasts. Subjects in Thomas' research burned 600-700 calories during one hour of running at about 80 percent of their maximum heart rate. During the next 48 hours, they burned about 15 percent more calories -- 90-105 extra -- than they otherwise would have. About 75 percent of the post-workout metabolism increase occurs in the first 12 hours after exercise, according to Thomas.

Weight training does not appear to offer as significant a post-workout metabolism increase as intense aerobic exercise, Thomas says, probably because of the rest between sets. A number of studies suggest that, after a 45-minute weight-training session -- three sets of 10 reps per exercise -- resting metabolic rate is increased for 60-90 minutes, burning an extra 20-50 calories. However, keep in mind that strength training is an excellent way to boost your resting metabolic rate (the number of calories your body burns at rest). While aerobics appears to offer more of a post-workout spike in metabolism, strength training enables you to develop muscle mass, which, in turn, increases metabolism overall.