The ideal way to do an exercise study, and the way that the hormone replacement question finally was answered, is to randomly assign one group of people to undergo a treatment (in this case, hormones) and another group to forego the intervention, and then wait to see who has better health. Such a study with exercise will never be done. No one knows how they could get people in one group to agree to exercise regularly for years and equal numbers in another group to agree to be sedentary. Even if they could, the study would require huge numbers of people to see an effect, because exercise, at best, creates relatively small changes in a population's health. For the foreseeable future, there is no choice but to accept, or dismiss, the large observational studies. I accept them, while realizing their limitations. If the studies have come to the wrong conclusion, all that would mean is that an imagined small benefit of exercise may in fact be nonexistent.

- Gina Kolata, Ultimate Fitness

Kolata, a science reporter for the NY Times and an avid exerciser, interweaves her discovery of the exercise program Spinning with her pursuit of the answers to some fundamental questions concerning health and exercise. Her questions include: what's maximum heart rate, is there a fat-burning zone, does increased muscle mass increase metabolism, and how much exercise is necessary.

The answers may come as a surprise, especially if what you know about exercise was gleaned from the ever present infomercials of the last decade. However, if you're a natural skeptic (which I confess to being) the answers confirm a belief that much of what's accepted as fact and common knowledge is based on flawed science and reaching for conclusions that don't flow from the data.

Take for example the case of maximum heartrate. There is a nearly ubiquitous belief that one's maximum heartrate is equal to 220 minus one's age. Kolata writes that this formula is based on an extremely limited data set, and that a better formula has been published that is 208 minus .7 times one's age. However, individual variation is so large (plus or minus 20 beats per minute), that even this formula has questionable usefulness.

Or, how much exercise is "enough." Truth is, no one knows. From the observational studies done, it appears that the health benefit from exercise comes mostly when people move from the lowest fifth of activity level to the next to lowest fifth. Beyond that, health effects are small or nonexistent. If the goal of exercise is weight loss or reshaping the body, then a much higher intensity and frequency of exercise is required. But, even then it appears that people's genetics dictate the degree to which they'll respond, if at all.

At the core, the book consists of an avid exerciser and journalist questioning the fitness industry and its claims and the science or pseudo-science that it rests on. It's an easy read that may equip the reader to evaluate other claims for themselves, or at least spur them to question the conventional wisdom.

The real question may be how these same principles might be applied to the common knowledge surrounding other areas, such as the environment, evolution, social science, etc. Where fields of endeavor require drawing conclusions from observational studies, one must always be skeptical. Conclusions can sound logical, and formulas may even be derived, but cause and effect are not known for certain and correlations prove naught. As noted by the author above, the consequences of believing the observational studies regarding exercise are relatively mild. When policies of governments are based on similarly questionable science, the stakes get much higher.

Note: Reviewed by Stephen