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Comment & Response
November 2019

Age-Related Bias in Total Step Count Recorded By Wearable Devices—Reply

Author Affiliations
  • 1Division of Preventive Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts
  • 2Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, Massachusetts
  • 3Laboratory of Epidemiology and Population Science, National Institute on Aging, Baltimore, Maryland
JAMA Intern Med. 2019;179(11):1603. doi:10.1001/jamainternmed.2019.4691

In Reply We thank Kuo and colleagues for their letter regarding our Original Investigation1 and agree that physical inactivity is a major public health problem in the United States and worldwide, which contributes to much ill health.2 Our main goal in conducting a study of step volume and intensity and their association with all-cause mortality was to provide information potentially useful for future physical activity guidelines.3 Current guidelines1 are couched in terms of recommended time spent in physical activity of moderate-to-vigorous intensity. This can be easily gauged by persons who purposefully exercise or walk for transportation; however, for those who may be active in their daily life (eg, someone who might actively play with children or grandchildren, or walk to the store to buy a replacement light bulb) but who do not intentionally exercise, it can be challenging to assess whether they are active enough to fulfill recommendations. Step counts may thus be a useful alternate metric, given the current ubiquity of step counters. Prior to our study, a widespread belief was that one needed 10 000 steps/d to achieve health benefit, which can be discouraging to inactive persons. Our findings indicated that 10 000 steps/d was not needed for lower mortality rates among older women who were not particularly active (mean step count of approximately 5500 steps/d).

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