Oprah uses weights to build muscle.

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The third and most important part of getting back on the wagon is the one Oprah says she dislikes most: exercise. "I have said for years how much I disliked it. And it's true—I really do," she says. "But I now realize that there is absolutely no way that I am going to be able to ever, ever maintain my weight without some regular cardio exercise."

Get Bob's "back to business" fitness plan.

One thing to keep in mind when you are doing a cardio workout is that it has to be hard enough that you actually get a benefit from it. How will you know when you're there? "You can talk, you can carry on a conversation, you can sing," Oprah says. "But you really don't want to. It'll be uncomfortable after a few minutes."

While cardio is still a major part of her workout, Oprah has altered her workout balance to include more resistance training and weight lifting. "The older you get, the more muscle mass you lose," she says. "Resistance training has proved to be really fascinating because, even though the weight isn't dropping the way I would like it to, I can see actually that my shape is changing—it's getting firmer and the clothes are getting looser. And that's all because of the weights."