A: "Curves can be great for novices," says Cedric X. Bryant, Ph.D., chief exercise physiologist for the American Council on Exercise. "It's a very comfortable, nonthreatening atmosphere."
However, Bryant cautions, the Curves workout -- a 30-minute machine circuit interspersed with cardio activity such as marching in place -- primarily offers strength-training, rather than cardiovascular, benefits. "It's a bit of an overstatement to say you don't need to supplement a Curves-type workout with aerobic conditioning," Bryant says. "Circuit training will cause improvements in aerobic capabilities, but they tend to be rather small."
Bryant recommends supplementing Curves workouts with three or four 30-minute cardio sessions each week, whether brisk walking, jogging, or using a cardiovascular machine such as an elliptical trainer or stair climber, to get sufficient results.
Instead of utilizing a traditional weight stack for resistance, the Curves machines have a series of pistons that create resistance by pumping fluid. The stronger you are -- and the more effort you exert -- the more resistance the machine automatically offers (up to a point), so you don't have to make adjustments to the machine. These hydraulic machines also differ from traditional weight machines in that they work different muscle groups during the lifting and the lowering phases. For instance, if you are doing a biceps curl on a hydraulic machine, you will feel resistance in your biceps when you bend, or curl, your arm, but when you return to the starting position by straightening your arm, you will feel resistance in your triceps.
In each full repetition on a hydraulic machine, you target two different muscle groups, which is very time-efficient. You're also likely to experience less muscle soreness than when using a machine with weight plates, since it is the lowering phase, or the "eccentric" contraction, that causes most muscle soreness. However, Bryant says, there's a downside. With less of a challenge in the eccentric phase, you won't gain as much muscle strength and won't see as significant an improvement in bone health. Also, he cautions, "there comes a point where the machine doesn't provide enough resistance. Inside of six months, you'll probably need a greater challenge, such as a workout with free weights or with machines that use weight plates."