Interventions
Participants used their own smartphones. Digital physical
activity tracking was performed using the Fitbug Orb (Chicago,
IL) (Figure S1), a wearable, display-free, triaxial accelerometer
that pairs with low-energy Bluetooth with compatible smartphones. The 3V lithium battery lasts around 6 months and thus
did not require charging or replacement during the trial.
Unblinded patients could continuously view their daily step
count, activity time, and aerobic activity time through smartphone and Web interfaces (Figure S2). The Fitbug app also
provided a history tab allowing review of data from previous
days. Activity data were updated every 15 minutes if transmission occurred by beacon mode or were available any time if a
participant activated a manual data push or streaming mode.
To enable real-time activity data to inform smart texts, we
linked the application programming interfaces of Fitbug and a
smart texting system (Reify, Baltimore, MD). Smart text
content was written by the physician investigators and
reflected behavioral change theories,
11
particularly of feedback loops and habit formation,
12
integrated with cardiovascular knowledge and clinical experience. Smart texts took into
account the importance of prescription writing and having a
specific, proximal goal; we used a goal of 10 000 steps/
day.
8,13–15
Each participant was a patient of a study physician
with texts aiming to leverage the physician-patient relationship, using the physician’s name in texts. Messages underwent content iterations to optimize language during pretrial
testing by the study team.