Excellent analysis of "facts" known about fitness and the economic motivation behind the fitness industry. Key points include how there is little research that supports the distinction between the "fat burning zone" and the "cardio" zone. All exercise, if done at an adequate level of intensity, will burn calories. More intense exercise, Kolata claims, will burn more calories than less intense exercse. She backs up her opinions with a solid review of the available literature, and concludes by asserting what makes the most sense: that your heart and your body will benefit from the hardest work that you can make it do.