Circuit Training: Take a Shortcut to Fitness (cont.)

"The stations are all set up with the right machines when I get to Curves," Magee says. "They are set to give more resistance the faster you go, so you don't have to adjust that. There are 15 machines. So you go on one machine for 30 seconds, and then jog on a pad for 30 seconds. Then you go on the next machine, and then jog. Once around [the machines] -- 15 minutes. We go twice around. Then you're done!"

A recording signals when to change machines or jog. Every 10 minutes, the exercisers check their heart rate.

"Ideally," says Wayne L. Westcott, PhD, fitness research director at the South Shore YMCA, in Quincy, Mass., "you get to 40% to 60% of maximum heart rate."

Why Circuit Training Works

"I am not there to lose weight, but to firm and tone," Magee says. "But I have noticed that my pants are looser."

Westcott cites the "classic" Cooper Clinic study done in 1982, which studied the effects of doing a circuit workout three times a week. The study had 77 participants, who were divided into three groups.

"One group did not train at all," Westcott says. "One group just did the weights. And the third group jogged in between the weight sessions."

Not surprisingly, the group that didn't train saw no improvement in its cardiovascular fitness. The weights group improved cardio fitness by 12%. And the weights-and-jogging group improved 17%. (The weights group also improved strength by 17% and the weights-and-jogging group improved strength by 22%.)

According to Westcott, a circuit workout improves both strength and endurance, and jump-starts metabolism.

"When those women leave the gym, they are still burning a third more calories than they did in the workout -- and this goes on for hours!" he says. "Once you build muscle, muscle burns more calories [than fat], so you continue to burn more."

Although weight training has traditionally been a male pastime (think Ah-nold), it's important for women, who tend to lose muscle mass at the rate of 1% per year in their late 30s and 40s. This muscle often gets replaced by fat. But you need muscles to cushion joints and help protect against osteoporosis, among other benefits. That's not to mention the trimmer, tighter appearance you'll gain by toning up.

Circuit training works because it's short and sweet and people actually do it. (Many gyms, as well as a chain called Health Inspirations, offer circuit training to both sexes.) "It's brief, it's basic, it's consistent; no frills, over quickly" is how Westcott puts it.

Is Circuit Training Enough?

But is a 30-minute workout enough? "I hate that question," says Cedric X. Bryant, PhD, chief exercise physiologist of the American Council on Exercise in San Diego. "Speaking purely scientifically, 30 minutes is probably not enough to maintain normal weight over a lifetime."

The Institute of Medicine recently recommended an hour of exercise a day.