VIEWPOINT Control arms in exercise training studies: transitioning from an era of intervention efficacy to one of comparative clinical effectiveness research

improves health, a number of clinically relevant scientific questions regarding physical activity require further inves-tigation (1). In this Viewpoint, we propose that physical activity research transition from determining efficacy, which has been well proven, to one of comparative clinical effec-tiveness research (3, 5). Clinical effectiveness research is a broad term used to encompass studies where rigid scientific control enabling determination of efficacy is traded for realistic situations in which the effectiveness of a treatment can be assessed within the context of comorbidities, com-munity barriers, noncompliance, and additional “real-world ” com-plications (7). Additionally, comparative clinical effectiveness studies emphasize the need for direct comparison of different treatments for which an efficacious treatment has been previously demonstrated (3, 5). We suggest that in investigations of physica