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

Abstract

Background: The aim of this study was to assess the ability of the Fitbit Charge 2 (FBC2) to accurately estimate VO 2max in comparison to both the gold standard VO 2max test and a non-exercise VO 2max 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). VO 2max was measured with an incremental test on the treadmill followed by a verification phase. VO 2max was predicted via a non-exercise prediction model (N-Ex) using self-reported physical activity level. Results: Measured VO 2max was significantly lower than FBC2 predicted CFS (VO 2max =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 VO 2max (N-Ex =48.79±6.32; CFS vs. N-Ex: P=0.01; VO 2max vs. N-Ex: P=0.54). Relationships between both VO 2max vs. CFS and VO 2max vs. N-Ex were good (ICC: VO 2max vs. CFS=0.87, VO 2max 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 VO 2max 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 VO 2max in healthy men and women. The non-exercise VO 2max prediction equation provides a similar, slightly more accurate, VO 2max prediction than the CFS without the need for an exercise test or purchase of a Fitbit.

Is a verification phase useful for confirming maximal oxygen uptake in apparently healthy adults? A systematic review and meta-analysis

“…The most common criterion used in the reviewed studies is that the highest VO 2 observed in the verification phase should not exceed 3% of the highest VO 2 obtained in the CPET. This threshold can be justified by the technical error of measurement and intra-individual biological variation associated with the determination of VO 2max [ 15 , 56 , 57 , 62 , 63 , 69 , 71 , 78 , 82 , 86 , 89 – 91 , 95 , 107 , 108 , 113 , 116 , 120 – 122 ]. The more restrictive value of ≤ 2% [ 97 , 110 ] and the less restrictive values of ≤ 5–5.5% [ 104 – 106 , 111 ] may also be appropriate for single or different-day variability.…”

Using wearable technology to monitor exercise intensity and predict V̇O2max

“…It is well known that "true" HR max can vary from APHRM (6). Moreover, in the case of the present study by Freeberg et al (1), introducing exercising HR data in response to speed-time data, was arguably adding "noise" to the estimation of "true" V O 2max . These investigators extrapolated an expected exercising HR from a series of laboratory tests (i.e., the observed HR values evoked for the outdoor test using the FBC2 were compared with expected HR values extrapolated by constant-paced treadmill bouts).…”

“…In summary, we appreciate the opportunity to provide commentary on the original investigation by Freeberg et al (1). We commend the authors for their important work and hope that our comments provide ideas for research and development of new technology along with testing methodology on existing wearable technology.…”

“…As new wearable technology emerges, empirical insight into usable fitness metrics such as accuracy for estimating V O 2max is warranted. We commend Freeberg et al (1) for their recent investigation of the FBC2 device and the manufacturer's protocol for estimating "true" V O 2max . The investigators compared the cardio fitness score from the FBC2 device with "true" V O 2max as measured with an incremental exercise test on a treadmill with a subsequent exhaustive verification bout.…”

“…In the case of the FitBit Charge 2 (FBC2) device, the parameters of speed, distance, and heart rate (HR) can be monitored and downloaded by the user. In the present Editorial Commentary, we discuss a recent study by Freeberg et al (1). These investigators examined the validity of the FBC2 device and the manufacturer's protocol for estimating maximum oxygen uptake (V O 2max ).…”