Lifestyle and Structured Interventions to Increase Physical Activity—Reply

In Reply: Drs Winett and Carpinelli make 3 good points that reinforce the public health implications of the study by Dunn and colleagues.¹ There were positive and enduring impacts on blood pressure and body fat with both structured exercise and lifestyle activity. Second, increased adherence to either protocol led to greater improvements in fitness, blood pressure, and total cholesterol levels. This important finding of a dose-response relationship between physical activity and improvements in cardiovascular disease risk factors was mirrored in the accompanying study by Andersen and colleagues.² A dose-response relationship is one of the necessary epidemiological criteria to demonstrate a causal relationship. Third, Winett and Carpinelli criticize the study by Dunn et al for the small increases in physical activity and fitness, but from a public health perspective, the association of beneficial changes in risk factors with these very small increases in physical activity and fitness is especially noteworthy. Modest increases in physical activity are often all that can be realistically obtained when trying to intervene in real-world settings with sedentary adults. The study subjects characterized by Winett and Carpinelli as "woefully unfit" are in fact representative of the majority of middle-aged Americans, and even small improvements in cardiovascular disease risk factors among this population will have a major public health impact.