A Better Body in 2 Hours a Week: A Total-Body Workout

The Benefits of an Intense Workout

Pumping up your routine -- adding intensity, trying new moves, and giving 100 percent -- does more than prevent workout boredom: It saves you a lot of time. "The thinking at the gym used to be, 'Well, at least I'm here,'" says trainer Tom Holland, author of The 12-Week Triathlete. But if you want to see big results fast, the new catchphrase should be "Go hard and go home," he adds.

Although the 2007 guidelines from the American College of Sports Medicine (ACSM) call for at least 30 minutes of exercise five or more days a week, they're based on moderate activity (think brisk walking) and are geared toward general health benefits, explains Bill Haskell, PhD, a professor at the School of Medicine at Stanford University and lead author of the ACSM report. Kick things up a notch and the recommendation is for just 20 minutes of vigorous activity (see "How Hard Is Hard Enough?" for examples) three times a week. Here's how to work out smarter, not longer.

One of the best-documented ways to shrink both your time commitment and your waistline is to incorporate intervals into your cardio routine. During this kind of workout (where you push the intensity as close to your max as you can -- an 8 or 9 on a scale of 1 to 10 -- for a short period of time), your muscles use more oxygen, increasing the amount of energy you spend, says Shawn Dolan, PhD, RD, a professor of kinesiology at California State University at Long Beach. "In a 30-minute interval routine, you have the potential to burn a third more calories than you would just going at a steady pace," she explains.

Interval training is also more effective at improving performance. Studies show that it increases both endurance and speed by improving the body's ability to use oxygen. Healthy college-age subjects who did short, high-intensity cycling workouts for just two weeks were able to bike longer (51 minutes compared to 26 minutes) and faster than before, according to a recent study from McMaster University in Ontario.

"When lifting weights, make sure you're constantly moving from one exercise to the next," says Holland. This nonstop action, aka circuit training, burns about 25 percent more calories than traditional resistance workouts by keeping your heart rate elevated the entire time. One of the most efficient strategies is to perform moves that target multiple muscle groups simultaneously. "This is how our bodies work in everyday life -- muscles are never isolated from one another when we move," says Holland. "Plus, by keeping your body guessing about what exercise is coming next, your muscles don't just automatically adapt to the routine without having to work hard." For moves to try, see "The Perfect Circuit," -- it should take 20 to 30 minutes.