Table 1 Contents of e-mail messages using the Health Action Process Approach (HAPA) model as the framework[27–29]

ORIENTATION

Preliminary meeting

Risk perception

· Information on the intervention, benefits of physical activity (PA), PA recommendations and walking

· Instructions on monitoring PA with a pedometer and a logbook and assessing the average number of daily steps at baseline

· Presentation of the ultimate goal of adding 4000 moderate-intensity steps to the baseline on 5 days of the week

MOTIVATIONAL PHASE (INTENTION BUILDING)

1^st e-mail

“Regaining strength by physical activity”

Within 2 weeks from the preliminary meeting

Positive outcome expectations, pre-action self-efficacy, action planning

· Benefits of integrating short bouts of PA into daily routine

· The 1^st goal of adding 2000 steps to the baseline on 2 days of the week

· Simple tips for accumulating 2000 steps

VOLITIONAL PHASE (INTENTION): PLANNING, PREPARING AND INITIATING PHYSICAL ACTIVITY

2^nd e-mail

“Finding time through experience”

4 weeks after the 1^st e-mail

Positive outcome expectations, risk perception, action planning, coping planning, self-monitoring

· Positive outcomes after even a short bout of PA

· Examples of finding time and places to be more active

· The 2^nd goal of adding 2000 steps to the baseline on 5 days of the week

3^rd e-mail

“Making physical activity one’s own thing”

4 weeks after the 2^nd e-mail

Positive outcome expectancies, risk perception, coping planning, maintenance self-efficacy, action planning

· Positive outcomes from being physically active

· Examples of accumulating 4000 steps

· The 3^rd goal of adding 4000 steps on 2 days and 2000 steps on 3 days of the week to the baseline

VOLITIONAL PHASE (MAINTENANCE)

4^th e-mail

“Preparing oneself against barriers”

4 weeks after the 3^rd e-mail

Action planning, coping planning, maintenance planning, maintenance self-efficacy

· The importance of regularity in PA

· The most critical barriers for PA and the ways to overcome them

· Example of a 30-minute walking session with 4000 steps

· The 4^th goal of adding 4000 steps on 4 days and 2000 steps on 1 day of the week to the baseline

5^th e-mail

“Getting oneself going”

4 weeks after the 4^th e-mail

Action planning, coping planning, maintenance self-efficacy, recovery self-efficacy

· Tips for making it easier to “get oneself going”

· The 5^th goal of adding 4000 steps to the baseline on 5 days of the week

6^th e-mail “Establishing a physically active lifestyle”

4 weeks after the 5^th e-mail

Action self-efficacy, maintenance self-efficacy, recovery self-efficacy, action planning

· Learning sustainable ways to be physically active

· The importance of regularity and the possibility of rewarding oneself

· Maintenance of current PA level and supplementation with muscle strengthening exercises on 2 days of the week

· A printable form for a weekly action plan and monitoring