The study, published in the Mayo Clinic Proceedings, intended to test whether a particular accelerometer device did an adequate job of monitoring a person's physical activity level.
While most news articles have latched onto the finding that obese men and women engage in very little "vigorous" exercise over the course of a year, the study examined less than week's worth of activities for each study participant and acknowledges limitations of the device used to measure activity. By its measures, normal weight and overweight individuals also engage in relatively little high-level physical activity.
The researchers write that the device they were testing to measure activity "underestimates the true level of physical activity because it captures only ambulatory movement and cannot accurately measure nonlocomotor activities." The device failed to accurately measure many types of exercises, such as swimming, bike riding, stair climbing or weight lifting.
In addition, while obese women did show only enough vigorous exercise during the study time period to equal about an hour over the course of an entire year, normal weight women's amount of vigorous exercise came out to just 10.95 hours per year. While it's significantly more than the obese women or overweight ones (3.65 hours), it's still not a huge amount of exercise.
The CDC's Physical Activity Guidelines for Americans recommend that adults get at least 2½ hours a week of moderate-intensity aerobic activity such as walking, or 75 minutes a week of vigorous-intensity aerobic activity, such as running, or a combination of both. This calculates to 3900 hours per year of vigorous exercise or 7800 hours of moderate physical activity.
The exercise study found that obese women engaged in moderate physical activity for the equivalent of 83.95 hours per year, overweight women 109.65 hours and normal weight women 127.75 hours.
The analysis showed that obese men engaged in the equivalent of 3.65 hours of vigorous activity per year, with 7.3 hours for overweight men and 10.95 hours for normal weight men. Obese men participated in moderate physical activity 142.35 hours a year, with overweight men clocking in at 186.15 hours and normal weight men at 211.7 hours.
The results of the study, which involved 2597 adults aged 20 and 74 years, seem to indicate that while obese and overweight individuals get less exercise than those of normal weight, few people of any weight category get the CDC's recommended amount of moderate or vigorous activity. However, the CDC says that "about 20 percent of U.S. adults are meeting both the aerobic and muscle strengthening components of the federal government's physical activity recommendations."