Within six months of its launch, Stanford's MyHeart Counts app had more than 47,000 users who agreed to participate in a study tracking their heart health. (credit: Norbert von der Groeben)

Widespread ownership of smartphones could potentially transform cardiovascular research by providing rapid, large-scale, and real-time measurement of individuals’ physical activity, according to a new study.

A free iPhone app — MyHeart Counts — gave users the ability to participate in a first-of-its-kind, easy-to-use cardiovascular research study. The app uses Apple’s ResearchKit framework, which gives potential users a simple way to measure daily activities, complete tasks, and answer surveys through their iPhone.

Within six months of the app’s launch, researchers had enrolled 47,109 participants from all 50 states who had consented to participate in the study. Researchers were able to collect data from 4,990 participants who completed a six-minute walk fitness test using the phone’s built-in motion sensors — a number several times larger than the largest study previously published.

The goals of the study are to provide real-world evidence of both the physical activity patterns most beneficial to people and the most effective behavioral motivation approaches to promote healthy activity. In most prior clinical studies, researchers relied on participants to estimate the time spent on physical activity. People have been consistently shown to overestimate their activity levels, the study noted. Mobile devices more directly measure people’s activity patterns throughout the day.