We looked at 3 distinct exposures. Physical activity type was categorized from questions asking about participation in various exercises and sports. The referent group was those subjects who reported no recreational activity participation (sedentary). Walkers were separated from runners and persons engaged in various strenuous and racquet sports were grouped together in a third "active" category. Total hours per week spent in physical activity was categorized into duration categories (<1.25, 1.25-3.75, >3.75) based on the moderate physical activity recommendations (30 minutes/day at least 5 times per week). Physical fitness categories were created from age and gender-specific quintiles of total time on treadmill in seconds. The bottom 20% of the treadmill time distribution was considered "low" fitness, the middle 40% "moderate" and the top 40% "high". These fitness categories have been used extensively in other health and fitness studies and correlate well with measured oxygen consumption.