Apple Heart and Movement Study

COVID, Activity Patterns, Physiology, and Stress

October 21st, 2020

How are exercise, cardiovascular health, stress, and general wellbeing related? We know that physical exercise reduces stress and, together, increased activity and lower stress are associated with beneficial long-term health outcomes. This knowledge has shaped general guidelines on living an active, healthy lifestyle, yet the mechanisms explaining these relationships are not entirely clear.

Everyday devices like the iPhone and Apple Watch can allow research studies to be conducted across a large population, by making it easy for users to participate from the comfort of their own home and voluntarily contribute relevant health research data. By capturing changes in stress, activity, and physiologic measures, over an extended period, it may be possible to define how and why these factors are so strongly related to each other. To truly understand these phenomena, we also need to know how individuals respond to shared challenges; the COVID-19 pandemic and associated changes in people’s personal and professional lives allow us to look at similarities and differences in responses to the same event across a population.

As one of our first efforts to understand the data in Apple Heart & Movement Study (AH&MS), we looked at how activity in general, and exercise in particular, changed in the context of the COVID-19 national emergency declaration on March 13th.


A few questions we asked to start analyzing this unique data set:

  • How did major changes in job status or work location impact activity levels, assessed by active energy burned, across the study population?
  • How did individuals who reported a marked increase in stress after mid-March compare in activity, assessed by step count, to those who remained at low stress levels?
Figure 1: Temporal trend in active energy burned in groups defined by job status.

The amount of energy burned follows a repeating pattern including a sharp drop on the weekends, but this changed substantially around COVID-19 shelter in place. From the recent COVID-19 Impact Survey answered by AH&MS participants, we can relate active energy patterns to job status, specifically those who began working from home, lost their jobs, or who had no change in job status. After March 13, 2020 (dashed vertical line), activity assessed through the median calories burned decreased across all groups, though the least difference was seen in those who had no change in job status. Those who began working from home have a pattern change where fewer calories were burned on weekdays relative to the weekend.

Figure 2. Temporal trend in median step count in groups defined by stress survey responses.

Median step count fell after March 13th, 2020 (dashed vertical line, labelled as post COVID), but is more pronounced in individuals with higher reported stress, as captured in survey (PSS-4) responses.

These initial data illustrate that measurements collected from personal devices combined with survey data provide an opportunity to study the impact of a shared experience on a large scale. Many other factors (including confounders) might explain these observations, including differences in Watch use patterns, local shelter in place orders, Spring break schedules, the types of work associated with changes in job, etc. Not least, there are significant differences in the way in which individuals respond to the same basic challenge. As the AH&MS evolves, we aim to build a more complete picture of the ways in which activity patterns, physiology, and stress are related.