What is your opinion of the new elliptical machines? Do they give you an effective workout, or is the treadmill a better option? Thank you.

How effective is the new Precor cross-training machine that is popping up in a lot of gyms? They say it is as good as running without hurting the knees.

The Precor elliptical cross-training machine is the hottest piece of aerobic equipment found in gyms right now. It's the Stairmaster of the late 90s. Loads of other companies are taking the elliptical motion concept and coming out with similar devices. Some machines are good while others are junk. They do provide a low-impact alternative to running, but they aren't any more or less effective than other cardiovascular equipment.

The effectiveness (or quality) of your workout depends on its intensity and duration. A person working out for one hour at 60 percent of her maximum heart rate isn't necessarily getting a better workout than someone working at 85 percent of her max for 45 minutes. (Remember we're not discussing calorie burning for weight loss, just overall quality in terms of fitness.)

All of the new elliptical devices give you a low-impact, aerobic workout. Models by Reebok, Cybex and other companies have handles so you can use your arms too. I've used the one made by Reebok, and it certainly gives a smooth ride. The handles and the action of the machine allow the user to simulate cross-country skiing even better than the NordicTrack.

One of the most compelling arguments in favor of these elliptical devices is the same reason you should be wary of relying exclusively on elliptical machines for your cardiovascular training: The lack of impact won't help maintain bone density, which prevents the loss of calcium in our bones.

You still need exercises like walking, running and weight-training exercises to help you maintain or increase your bone density. Never depend on one exercise or one type of machine.

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