Table 2.

Major issues identified with the BNT app during the usability study.

Issue #	Participants	Task	Issue
A1	P1, P2, P4	Education	Poor organization and presentation of information resulted in a lack of understanding of core concepts (HRV a, RSA) required to interpret key sections of the app (Biofeedback, BNT, performance reviews).
A2	P1, P4, P5	Biofeedback	Biofeedback mechanism (heart rate and goal) was not always clear. Users were unsure of what to expect and whether they were completing the exercise correctly. Future interventions should consider a simpler and more intuitive interface that does not require users to comprehend complex medical terminology.
A3	P1, P4, P5	Review	Interpreting the performance review was difficult. It was not immediately obvious whether user results match the goal. Similarly, users should be presented with a simple display of success, providing cues on how to improve the next time.
A4	P4	Biofeedback	Biofeedback screen with audio creates information overload. User attention is divided between paced breathing, heart rate wave, and audio instructions on stress countering steps.

^aBNT: behavioral neurocardiac training, HRV: heart rate variability, RSA: respiratory sinus arrhythmia.