As part of the study, the nurses periodically fill out questionnaires about their health, weight, diet and behavior.
The new analysis, published in the June 28 issue of /*Archives of Internal Medicine*/, looked at weight change and behavior from 1989 to 2005.
Researchers found women in their 30s and 40s who increased physical activity like brisk walking and bicycling by 30 minutes a day during the 16-year period maintained their weight and even lost pounds.
But those whose exercise was slow walking did not lose any weight.
Anne C. Lusk, a research fellow at the /*Harvard School of Public Health*/ and author of the paper said the findings are "highly suggestive that bicycling is highly beneficial in women."