JMIR Publications

ABSTRACT

Background:

Remote monitoring of physical activity in patients with chronic conditions could be useful to offer care professionals real-time assessment of their patient’s daily activity pattern to adjust appropriate treatment. However, the validity of commercially available activity trackers that can be used for telemonitoring purposes is limited.

Objective:

The purpose of this study was to test usability and to determine the validity of four consumer-level activity trackers as a measure of free-living activity.

Methods:

A usability evaluation (study 1) and validation study (study 2) were conducted. In study 1, ten individuals each wore one activity tracker for a period of 30 days and filled in a questionnaire on ease of use and wearability. In study 2, we validated four selected activity trackers (Apple Watch, Misfit Shine, iHealth Edge and Yamax Digiwalker) against the reference standard (Actigraph GT3X) in 30 healthy participants for 72 hours. Outcome measures were 95% limits of agreement (LoA) and bias (Bland-Altman analysis). Furthermore, median absolute differences (MAD) were calculated. Correction for bias was estimated and validated using leave-one-out cross validation.

Results:

Usability evaluation of study 1 showed that iHealth Edge and Apple Watch were more comfortable to wear as compared to the Misfit Flash. Within study 2, the total number of steps of the reference standard was 21527 (IQR: 17475-24809). Bias and LoA for number of steps from the Apple Watch, and iHealth Edge were 968 (-5478 to 7414) and 2021 (-4994 to 9036) steps. For Misfit Shine and Yamax Digiwalker, bias was -1874 and 2004, both with wide LoA of (13869 to 10121) and (-10932 to 14940) steps respectively. The Apple Watch noted the smallest MAD of 7.7% with the Actigraph, whereas the Yamax Digiwalker noted the highest MAD (20.3%). After leave-one-out cross validation, accuracy estimates of MAD of the iHealth Edge and Misfit Shine were within acceptable limits with 10.7% and 11.3% respectively.

Conclusions:

Overall, the Apple Watch and iHealth Edge were positively evaluated after wearing. Validity varied widely between devices, with the Apple Watch being the most accurate and Yamax Digiwalker the least accurate for step count in free-living conditions. The iHealth Edge underestimates number of steps, but can be considered reliable for activity monitoring after correction for bias. Misfit Shine overestimated number of steps and cannot be considered suitable for step count due to the low agreement. Future studies should focus on the added value of remotely monitoring activity patterns over time within chronic patients.