Editor's Note
May 20, 2024
Tracking Physical Activity One Step at a Time
Cary P. Gross, Raegan W. Durant
JAMA Intern Med. Published online May 20, 2024. doi:10.1001/jamainternmed.2024.0898
Current physical activity guidelines recommend at least 150 minutes per week of moderate-intensity physical activity or 75 minutes per week of vigorous activity. These time thresholds were based on studies using self-reported activity, which is prone to bias. Moreover, asking people to keep track of their time spent exercising each week may be adding yet another hurdle to enhancing activity levels.
Rather than assessing the amount of time exercising, daily step counts may be a more attractive way of measuring physical activity. Many people have mobile devices with built-in accelerometers, with their daily steps counted as a matter of routine. A fundamental question, however, is whether step counts are a reliable way of assessing beneficial physical activity.
To address this gap, Hamaya et al1 provided accelerometers to more than 14 000 participants in the Women’s Health Study who were 62 years or older and asked them to wear the accelerometers for 7 consecutive days. The researchers tracked both the amount of moderate to vigorous physical activity (a time-based approach) and the total number of steps during this interval. After a median follow-up of 9 years, they found that each of these metrics was associated with decreased risk of death and cardiovascular disease. For instance, among participants whose baseline activity exceeded the recommended physical activity time of 150 minutes per week, the risk of all-cause mortality was 32% lower than participants in the lowest quartile of time spent exercising. Similarly, patients averaging more than 7000 steps per day had a 42% lower all-cause mortality than patients in the lowest quartile of steps. Thus, both metrics were associated with mortality risk.
However, the consumer-grade step counters used in this study are distinct from smartphone applications. Although step counters that are incorporated into mobile phones may not be as accurate, given the near ubiquity of smartphones, assessing whether step counts derived from phones can be used as a valid marker of activity will be crucial in the future.
These findings may begin to lay the groundwork for step counts being used as a much more comprehensible and applicable basis for setting physical activity goals both in individual patient interactions and in broader formal physical activity guidelines. Additional studies are needed to duplicate this work in different populations including not only men and younger age groups, but also racially and ethnically minoritized populations and lower-income populations that frequently have less time and physical space for structured exercise.2 Although these socioeconomically disadvantaged and underserved groups may more easily engage in physical activity by walking or simply incorporating more steps into their daily routines (eg, taking stairs), additional efforts will be essential to mitigate barriers in their local built environments. Moreover, the inclusion of step counts in prescriptions for exercise and formal physical activity guidelines relies on the use of step counts as a metric in both future randomized clinical trials and large observational studies. This future research will strengthen the evidence base linking step counts to relevant health outcomes. Time spent in dedicated physical exertion compared with step counts reflects related yet differing aspects of physical activity, and both are highly relevant to improving clinical outcomes including mortality. Capturing both metrics in future research will help to advance research on physical activity and health.
