Cancer survivors generally have low physical activity (PA) levels. While literature shows some evidence of improvement in PA following technology-based PA promotion interventions among cancer survivors, high-quality randomised control trials (RCTs), with objective measures of PA and longer-term follow-up, are lacking. Using a theoretical framework that addresses action control in addition to intention formation may enhance intervention effect. The Multi-process action control (M-PAC) framework is an extension of the traditional intention-formation theories, incorporating constructs that address the translation of intention into behaviour and continual action control. After comprehensively searching, no previous or ongoing RCTs have investigated the efficacy of a technology-based PA promotion intervention in cancer survivors that is designed based on the M-PAC framework. Investigators therefore propose a RCT to evaluate a technology-based intervention (WExercise) to support the promotion of PA in cancer survivors.

Objective: To develop a technology-based physical activity promotion intervention (WExercise) for cancer survivors based on the Multi-process Action Control (M-PAC) Framework and examine its usability and efficacy.

Main hypothesis: The WExercise group will have a significantly greater increase in aerobic exercise than the self-directed exercise group at post-intervention.

Design: Phase 1- Application development; Phase 2- Usability testing (n=10); Phase 3- Assessor-blind two-arm randomized controlled trial (n=98; WExercise or self-directed exercise group).

Subjects: Physically inactive cancer survivors who have completed curative treatment.

Study instruments: Accelerometry, Godin Leisure Time Exercise Questionnaire, 6-minute walk test, EORTC QLQ-C30, M-PAC questionniare; administered at baseline, post-intervention, and 3 months post-intervention.

Interventions: Both groups will receive written physical activity guidelines with a goal to engage in at least 150 minutes of moderate-intensity or 75 minutes of vigorous-intensity aerobic exercise per week. The WExercise group will additionally receive 10 weekly automated online classes delivered on a mobile application which aim at developing participants' reflective, regulatory, and reflexive processes based on the M-PAC to achieve recommended physical activity levels (1st-3rd week: intention formation; 4th-8th weeks: behavioral regulations; 9th-10th weeks: action control maintenance).

Main outcomes: Time spent in moderate-to-vigorous aerobic exercise (primary), exercise capacity, and quality of life.

Data analysis: Intention-to-treat analysis will be performed. Application usage in the WExercise group will be presented in descriptive statistics. Generalized linear mixed-effect models will be used to assess between-group and within-group differences in the outcomes.

Expected results: The findings will inform the design of future eHealth interventions to encourage and sustain health behavior change in cancer survivors.

Inclusion Criteria:

• ≥18 years of age
• completion of primary treatment (surgery/chemo-/radiation therapy) of curative intent for at least 12 months,
• no metastasis, no recurrence
• not meeting the recommended PA guideline (<150 min of moderate intensity aerobic exercise and <75 min of vigorous aerobic exercise per week)
• access to Internet
• able to read Chinese and communicate in Cantonese or Putonghua
• screened by a nurse as no contraindications for engaging in unsupervised exercise using a risk screening tool

Exclusion Criteria:

• have a psychiatric disorder
• significant cognitive impairment
• a history of more than one cancer