Feasibility of a web-based randomised controlled trial for a tailored physical activity intervention

active-online.ch is a freely available Internet-based physical activity counselling programme disseminated population-wide with a multimedia strategy. The feasibility of an Internet-based randomised controlled trial was tested in a small-scale study. Participants were recruited using print advertisements, Internet banners and e-mail messages. After baseline assessment, they were randomised to the intervention programme active-online.ch or a control website. Participants were re-contacted by e-mail after six weeks and six months for follow-up assessment. E-mail invitations in an administration unit and a print advertisement were most effective for recruitment. After six weeks, complete data was available from 76% of the original participants, after six month from 63%. 48% of the original subjects were women, 76% between 30 and 60 years old and 57% insufficiently active. At every stage
of the study, the proportion of women in the trial decreased significantly. 35% of the participants in the intervention group completed the intervention programme. For future full-scale randomised trials using an Internet design, recruitment should be planned in
view of the implementation strategy of the intervention. Expected adherence to both the study protocol and the physical activity intervention need to be considered when sample sizes are estimated.