Background: The widespread incorporation of behavioral support interventions into exercise trials has sometimes caused confusion concerning the primary purpose of a trial. The purpose of the present paper is to offer some conceptual and methodological distinctions among three types of exercise trials with a view towards improving their design, conduct, reporting, and interpretation.
Discussion: Exercise trials can be divided into "health outcome trials" or "behavior change trials" based on their primary outcome. Health outcome trials can be further divided into efficacy and effectiveness trials based on their potential for dissemination into practice. Exercise efficacy trials may achieve high levels of exercise adherence by supervising the exercise over a short intervention period ("traditional" exercise efficacy trials) or by the adoption of an extensive behavioral support intervention designed to accommodate unsupervised exercise and/or an extended intervention period ("contemporary" exercise efficacy trials). Exercise effectiveness trials may emanate from the desire to test exercise interventions with proven efficacy ("traditional" exercise effectiveness trials) or the desire to test behavioral support interventions with proven feasibility ("contemporary" exercise effectiveness trials). Efficacy, effectiveness, and behavior change trials often differ in terms of their primary and secondary outcomes, theoretical models adopted, selection of participants, nature of the exercise and comparison interventions, nature of the behavioral support intervention, sample size calculation, and interpretation of trial results.
Summary: Exercise researchers are encouraged to clarify the primary purpose of their trial to facilitate its design, conduct, and interpretation.