BACKGROUND: As the number of cancer survivors is increasing, it is important to be able to offer exercise and physical activity (PA)-promoting interventions that are both effective and reasonably accessible. Internet-based interventions are typically less expensive and more accessible alternatives to on-site supervised interventions. Currently, little is known about the characteristics of nonparticipants in PA promotion trials in the cancer survivorship setting, both in general and specifically in trials using internet-supported interventions.

OBJECTIVE: This study aims to gain insight into the characteristics associated with nonparticipation in a blended internet-based supported intervention trial to promote PA.

METHODS: Breast and prostate cancer survivors, 3-36 months after primary curative treatment, were invited to participate in the PABLO trial; this trial compared an internet-based intervention to enhance PA levels, with or without additional support from a physical therapist, to usual care. Participants and nonparticipants were asked to complete a comprehensive questionnaire assessing sociodemographics, fatigue, and health-related quality of life. Baseline data for participants and nonparticipants were compared using the independent Student t test and chi-square test.

RESULTS: The inclusion rate in the trial was 11.03% (137/1242). Of the nonparticipants, 13.95% (154/1104) completed the questionnaire. Participants were more highly educated (P=.04), had a paid job less often (P=.03), and were on sick leave more often (P=.03). They reported less PA per week, both moderate (P=.03) and vigorous (P<.01), before diagnosis and during leisure time (P<.01, effect size [ES]=0.44). They reported a significantly lower stage of change (P≤.01), lower self-efficacy (P<.01, ES=0.61), perceived barriers to PA (P<.01, ES=0.54), and more general fatigue (P<.01, ES=0.60). Participants reported lower health-related quality of life for most domains (ES ranging from 0.34 for mental health to 0.48 for social functioning). No significant differences were found for other sociodemographics, mood state, or attitudes toward or perceived social support for PA.

CONCLUSIONS: The participants who self-selected for trial participation reported lower PA levels before diagnosis and a stronger need for support compared with nonparticipants. The trial thus included those patients who might benefit the most from internet-based supportive PA interventions.

TRIAL REGISTRATION: Netherlands trial register NTR6911; https://www.trialregister.nl/trial/6733.