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. 2019 Sep 23:5:39.
doi: 10.21037/mhealth.2019.09.07. eCollection 2019.

Assessing the ability of the Fitbit Charge 2 to accurately predict VO2max

Kaitlin A Freeberg  1 , Brett R Baughman  1 , Ted Vickey  1 , Jeff A Sullivan  1 , Brandon J Sawyer  1
Affiliations

Assessing the ability of the Fitbit Charge 2 to accurately predict VO2max

Kaitlin A Freeberg et al. Mhealth. .

Abstract

Background: The aim of this study was to assess the ability of the Fitbit Charge 2 (FBC2) to accurately estimate VO2max in comparison to both the gold standard VO2max test and a non-exercise VO2max prediction equation.

Methods: Thirty healthy subjects (17 men, 13 women) between the ages of 18 and 35 (age =21.7±3.1 years) were given a FBC2 to wear for seven days and followed instructions on how to obtain a cardio fitness score (CFS). VO2max was measured with an incremental test on the treadmill followed by a verification phase. VO2max was predicted via a non-exercise prediction model (N-Ex) using self-reported physical activity level.

Results: Measured VO2max was significantly lower than FBC2 predicted CFS (VO2max =49.91±6.83; CFS =52.53±8.43, P=0.03). N-Ex prediction was significantly lower than CFS but not significantly lower than measured VO2max (N-Ex =48.79±6.32; CFS vs. N-Ex: P=0.01; VO2max vs. N-Ex: P=0.54). Relationships between both VO2max vs. CFS and VO2max vs. N-Ex were good (ICC: VO2max vs. CFS=0.87, VO2max vs. N-Ex =0.87); Bland-Altman analysis indicated consistency of CFS measurement and lack of bias. The coefficient of variation (CV) and mean absolute percent error (MAPE) were greater with CFS than N-Ex (CV: CFS =6.5%±4.1%, N-Ex =5.6%±3.6%; MAPE: CFS =10.2%±6.7%, N-Ex =7.8%±5.0%). Heart rate (HR) estimated by the FBC2 was lower than estimated (Est) HR for pace based on HR extrapolation (FBC2 =155±18 bpm, Est =183±15 bpm, P<0.001). The difference in CFS and VO2max was inversely correlated with the difference in FBC2 HR and Estimated HR (r =-0.45, P<0.001).

Conclusions: The FBC2 shows consistent, unbiased measurement of CFS while overestimating VO2max in healthy men and women. The non-exercise VO2max prediction equation provides a similar, slightly more accurate, VO2max prediction than the CFS without the need for an exercise test or purchase of a Fitbit.

Keywords: Cardiorespiratory; Fitbit; VO2max; cardio; exercise; fitness; heart; rate; score.

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Conflict of interest statement

Conflicts of Interest: The authors have no conflicts of interest to declare.

Figures

Figure 1
Figure 1
Bland-Altman plot of mean and difference between measured VO2max and FBC2 CFS. The solid line represents the mean difference of −2.92 mL/kg/min and the dashed lines are the 95% limits of agreement. FBC2, Fitbit Charge 2; CFS, cardio fitness score.
Figure 2
Figure 2
HR values from FBC2 and extrapolation. The line is the line of identity. FBC2, Fitbit Charge 2.
Figure 3
Figure 3
Differences between extrapolated HR and FBC2 Measured HR in relation to differences between measured VO2max and CFS. FBC2, Fitbit Charge 2; CFS, cardio fitness score.
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