And the programs have never before been so intense. (Try doing P90X after eating Cheerios.) Hilary Raupp, 40, had grown bored of her gym. But “I wasn’t looking for a Jane Fonda riff,” said Ms. Raupp, a homemaker who lives in Doylestown, Pa. “I was looking for a real program.” So she bought “Insanity,” an extreme interval-training DVD series that she said cost $180.

“I love it,” Ms. Raupp said, and since her old gym cost $100 a month for both her and husband, plus $8 to $25 more when they took a class, “we saved money by month three.”

You might think that working out at home without a trainer would lead to more injuries, but Dr. Thomas M. Best, a director of the division of sports medicine at Ohio State, said no evidence supports that, though he stressed that if you have a condition like heart disease or diabetes, you should check with a doctor before beginning an at-home program.

Offering further credence to the genre, professional instructors and gyms, rather than models and actresses, are increasingly headlining videos. This month, Canyon Ranch began selling its first fitness DVD, “Canyon Ranch: Strong & Sculpted” ($16.99), set amid cactuses in the Tucson desert. “We really just wanted to be able to offer an opportunity for individuals to have the experience of Canyon Ranch that don’t have the financial ability to come,” said Heather Schmidt, a fitness instructor at the ranch, who is also in the new video.