Fitbit readings highlight lingering physiological, behavioral changes after COVID-19 infection

Newly published data from a longitudinal study of Fitbit users describe activity, sleep and resting heart rate changes triggered by COVID-19 infection that often last weeks and months after the first signs of symptoms.

The duration of the impact varied widely from person to person but was most persistent when measuring individuals’ resting heart rates, researchers from Scripps Research Translational Institute (SRTI) wrote in JAMA Network Open.

Specifically, after initially experiencing brief moments of reduced resting heart rate, Fitbit users with COVID-19 logged elevated resting heart rates that lasted an average 79 days after the onset of their symptoms. Participants’ step counts and sleep quantity, meanwhile, returned to normal after an average 32 and 24 days, respectively.

“Long-term COVID symptoms marked by autonomic dysfunction and cardiac damage following COVID-19 infection have been noted for up to six months after symptom onset, but to date have not been quantified, to our knowledge,” the researchers wrote. “Wearable devices provide a way to continuously track an individual’s physiological and behavioral metrics beginning when healthy (i.e., before infection), during the course of infection and recovery back to baseline.”

The researchers also noted that the resting heart rates of some participants with COVID-19 (13.7%) remained more than five beats per minute greater than their baseline for more than 133 days after symptom onset. Compared to other participants, these individuals more frequently reported symptoms such as coughing, body aches and shortness of breath during their initial illness.

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“Our data suggest that early symptoms and larger initial [resting heart rate] response to COVID-19 infection may be associated with the physiological length of recovery from this virus,” they wrote.

These findings are the latest from the DETECT Study, SRTI’s ongoing research effort to glean COVID-19 insights from wearables like Fitbits, Apple Watches or Garmins.

Launched in March 2020, the project asks adult participants to download a study app that connects to and uploads biometric data from their smartwatch or fitness tracking device. Participants also log whether they are experiencing symptoms or have received any results from a COVID-19 diagnostic test.

For its most recent findings, the SRTI team reviewed data from 875 Fitbit users who reported acute respiratory illness and received COVID-19 between March 25, 2020, and Jan. 24, 2021. Of these, 234 participants received a positive test result, and 641 received a negative result and were likely experiencing a different respiratory illness.

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Comparing these two groups showed that participants with confirmed COVID-19 took longer to return to their resting heart rate, sleep and activity baselines than those with a negative test.  

The researchers noted they were unable to compare the persistent physiological and behavioral changes to potential long-term symptoms of COVID-19, as they did not collect data on participants’ symptoms outside of their initial illness.

These latest data follow early DETECT results released by SRTI last fall suggesting that the wearable-detected changes in heart rate, sleep and activity could support early detection of COVID-19.

While Fitbit encouraged many of its users to join SRTI’s study, the wearables maker has also come out with its own study data floating the possibility of predicting COVID-19 hospitalization using data collected by the devices.

“Research to understand the long-term impacts of COVID-19 on health and well-being is incredibly important, and wearables such as those from Fitbit continue to have a vital role in these efforts,” John Moore, M.D., medical director at Fitbit, told Fierce Healthcare in a statement. “Fitbit's published research has shown that metrics like breathing rate, resting heart rate and heart rate variability (HRV) can offer useful insights into disease onset and effects on the body. We are pleased that our ongoing collaboration with Scripps Research has yielded new findings about the impact of COVID-19 over time, which further highlights the potential for wearables data in early detection of acute illness and chronic conditions beyond the current pandemic.”