Current health policies state that the greatest health benefits will be achieved by increasing physical activity among the least active individuals. This presumption is based largely on studies of cardiorespiratory fitness, which is often treated as a surrogate measure of physical activity. However, physical fitness and activity are not the same; physical activity is the voluntary movement by skeletal muscles that results in energy expenditure, whereas cardiorespiratory fitness is the ability to supply oxygen during sustained physical activity. We therefore decided to test whether fitness and physical activity provide the same protection from cardiovascular disease. This test combined the results of different published studies into two separate graphs, one for physical activity and one for fitness, to see whether they were the same. The technique for combining studies is called meta-analysis. Because physical activity and fitness are measured in different units (calories versus VO2max), we needed to find a common scale to compare them. We accomplished this through plotting the cumulative percentages of the samples from least fit or active, to most fit or active. This assumed that if you rank at the 40% in activity you would also be at the 40% of fitness, a reasonable assumption if indeed activity and fitness are the same. One challenge of meta-analysis is to find all the relevant studies. The recently published Surgeon General's report on Physical Activity provided a comprehensive list of population-based studies that followed individuals over time. In these studies, causes of death or clinical events during the follow-up period were compared to baseline (starting) levels of physical fitness or physical activity. Since the Surgeon General's physical activity recommendations are based on the studies listed in the report, this was the logical resource for making the comparison. The Surgeon General's report listed forty studies which compared physical activity levels to the risk of developing coronary heart disease (CHD) or cardiovascular diseases (CVD, including both CHD and stroke). It also listed eleven papers on