Table 3.

Methods and practical applications used in the intervention for the volitional phase.

Methods	Determinants	Practical applications
Selecting hindering factors/barriers and solutions Implementation intentions	Action planning Coping planning	Adults can first select hindering factors and barriers out of a predefined list. When applicable hindering factors and barriers are not available in the list, participants also have the possibility to write down another factor or barrier in an open-ended format. Next, participants can select solutions out of a predefined list or write down another solution. Afterward, participants are stimulated to make action plans and coping plans by formulating if-then plans (ie, “implementation intentions”). After the “if,” a situation or the previously selected difficult situations or barriers are stated and after the “then” the selected action or solutions to overcome the difficult situations and barriers are stated (eg, If it is Monday evening and I am not in the mood for sports, then I call my friend to go to the aerobic lessons together). Adults can formulate this implementation intention plan in an open-ended question format on the website.
Goal setting	Action planning	A list with personal and relevant goals is formed based on previous answers; adults can select the goals to change that they are confident about.
Stating SMARTagoals	Action planning	Adults are guided by questions to make a specific, measurable, attainable, relevant, and time-bound (SMART) action plan. For example, adults can formulate answers to questions on what they want to do (eg, increase physical activity by biking 20 minutes to work), how often (eg, three times per week), when (eg, Monday, Wednesday, and Friday), and when they want to start (eg, starting on Monday, July 7). After answering all the questions, the personal action plan and the if/then plan are automatically generated and sent by email to the participant.
Public commitment	Social support	Adults can choose to send their action plan to others (eg, family and friends) to ask them to support them and invite them to also make an action plan.
Prompt self-monitoring of behavior and prompt review of behavioral goals	Action planning Maintenance self-efficacy	Adults are asked to keep a record of their physical activity levels or fruit and vegetable intakes by one of the given suggestions (ie, personal paper agenda, mobile phone, Excel sheet, or online agenda). After the active goal pursuit was started, adults are also invited by email to report their behavior on the website. Periodic email reminders are sent to invite adults to fill out a questionnaire about the target behavior and their goals on the website. The results are compared with their previous behavior and goals, and iterative feedback is provided on the progress of behavior change.
Set tasks on a gradient of difficulty	Maintenance self-efficacy	When adults have attained their goals, they are invited to change the goal by reformulating a more attainable or more difficult goal or by setting additional goals.
Planning coping responses	Coping planning Maintenance self-efficacy	Adults are asked whether they experienced barriers while pursuing their goals. If so, they are invited to identify solutions to cope with the identified situations or barriers. Adults can again select solutions from a list that is generated based on the selected difficulties.
Prompt review of behavioral goals and personal feedback	Recovery self-efficacy	When people do not achieve their goals, people get personal feedback that informs them that relapse is normal. They are also advised to try again, to choose other strategies, or to adapt their goals to more attainable goals.

^aSMART: specific, measurable, attainable, relevant, and time-bound.