Who participates in physical activity intervention trials?

Taking a representative snapshot of physical activity intervention trial findings published between 1996 and 2006, we empirically evaluated participant characteristics, response and retention rates, and their associations with intervention settings.

A structured database search identified 5 representative health behavior journals, from which 32 research reports of physical activity intervention trials were reviewed. Interventions settings were categorized as workplace, healthcare, home- or community-based. Information on participant and intervention characteristics was extracted and reviewed.

The majority of participants were Caucasian (86%), women (66%), healthy but sedentary (63%), and middle-aged (mean age = 51 years). Intervention response rates ranged from 20% to 89%, with the greatest response rate for healthcare and home-based interventions. Compared with nonparticipants, study participants tended to be women, Caucasian, tertiary-educated, and middle-class. Participants in workplace interventions were younger, more educated, and healthier; in community-based interventions, participants were older and more ethnically diverse. Reporting on education and income was inconsistent. The mean retention rate was 78%, with minimal differences between intervention settings.

These results emphasize the need for physical activity interventions to target men, socioeconomically disadvantaged, and ethnic minority populations. Consistent reporting of response rate and retention may enhance the understanding of which intervention settings best recruit and retain large, representative samples.