We conducted focus group meetings to discuss the content, features and design of the app.

The focus group consisted of physiotherapists and young adults. The focus group members discussed the variety of topics in subgroups (login parameters, self-monitoring, exercises content, video or animation types, exercise diary, reminders, encouragement, method, etc).

We tested the prototype version app interface in the 2nd phase. All participants downloaded the prototype app and used the app for one week.

We conduct a think-aloud interview and evaluate the quantitative usability in the third phase.

The quantitative usability was assessed by the System Usability Scale (SUS), and the adapted Usability, Satisfaction and Ease to Use (USE) Questionnaire.

The app-based group:

Participants in the intervention group received their smartphone-based- home exercise program.

The control group:

Participants in the control group received their home exercise programs as a paper handout.

Participants received home exercise programs by a postural alignment exercise mobile app we developed.

The postural alignment app included 3 main emerged themes were recorded as self-assessment, neck/shoulder, and upper back-specific exercise content, and motivational notifications.

Participants can evaluate themselves in the application thanks to the self-assessment, receive motivational notifications during the day, and exercise reminders on the days determined by them. They can apply the exercise program with the formed exercise content videos.

The exercise program consists of combined exercises that postural alignment plus exercises of neck spinal stabilization, stretching, and strengthening of neck/shoulders/upper back regions.

Both group participants were requested to do the exercises from the app/brochure 3 times a week, for 6 weeks.

Musculoskeletal problems were assessed by Nordic Musculoskeletal Questionnaire. The Nordic Musculoskeletal Questionnaire queries yes/no for nine body regions so far, in the last 12 months, and in the last 7 days of evaluation, whether ache, pain, or discomfort.

Neck pain was assessed by Visual Analog Scale (VAS) before and after the 6 weeks exercise program. The participants were instructed to mark a point on a line between zero (no pain) and 10 cm (maximum pain).

Functional disability associated with neck pain was evaluated by the Neck Pain and Disability Scale (NPAD) questionnaire before and after the 6 weeks exercise program. The Neck Pain and Disability Scale consists of 20 items and each item was scored from 0 to 5, and the total score is the sum of the item scores [possible range 0 (no pain)-100 (maximal pain)].

The app automatically gathers total usage status (count of participated sessions, usage times) when participants login to the app to start an exercise program.

Exercise adherence was measured with a ratio of total participated sessions compared with the target defined.