This pilot study will evaluate possible intervention components to be included in a future stress management and health behaviour change trial and to pilot test their feasibility and acceptability in a small sample.

Work is one of the greatest contributors to chronic stress. Chronic stress is a critical risk factor leading to several negative work- and health-related outcomes. Developing scalable stress-management interventions will improve workers' health and wellness. The purpose of this project is to develop an optimized a stress reduction behavioural coaching and biofeedback intervention to supplement an existing mHealth platform (consisting of behavioural web-based modules). By testing coaching and biofeedback, this project can determine what level of interaction with a trained coach is necessary to optimally reduce workers' stress, and improve their health and well-being. To achieve this purpose, the multiphase optimization strategy (MOST) will be employed to develop, optimize, and evaluate the efficacy of this intervention. The three-phases include: preparation (selecting which intervention components are feasible to examine), optimization (determining the optimized package of components), and evaluation (evaluating the efficacy of the optimized package through a randomized control trial). This trial will cover the first phase of the MOST protocol. This pilot study will evaluate possible intervention components to be included in a future stress management and health behaviour change trial and to pilot test their feasibility and acceptability in a small sample.

Preparation phase objectives:

1.1 Determine which candidate components will be tested in a later optimization phase and at what dose they will be tested 1.2 Examine the feasibility of delivering the different components 1.3 Examine the acceptability of delivering the different components 1.4 Evaluate whether the outcomes can be feasibly measured

Design overview: A 2^4 (2x2x2x2) factorial experiment will run in the next phase of this project to test all combinations of four candidate components "turned on and off" with 16 different conditions. In the present study, we will ask 16 participants to each participate in and evaluate one of the sixteen conditions. The four candidate components being tested are: Daily resting HRV biofeedback, Momentary HRV biofeedback, Behavioural initiation coaching, and Practice with feedback coaching. Additionally, all participants will be asked to use complete the 8-week health behaviour change and stress management program on the Core health mHealth platform. Participants will be randomized to completing one of the sixteen conditions while completing the eight-week CoreHealth program.

Inclusion Criteria:

• 18 years and older
• Able to read and comprehend English
• Have smart phone (Android or iPhone 8 or higher)
• Self-report BMI under 40
• report at least Moderate daily stress

Exclusion Criteria:

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