Performance of a commercial multi-sensor wearable (Fitbit Charge HR) in measuring physical activity and sleep in healthy children

Abstract

Purpose: This study sought to assess the performance of the Fitbit Charge HR, a consumer-level multi-sensor activity tracker, to measure physical activity and sleep in children.

Methods: 59 healthy boys and girls aged 9-11 years old wore a Fitbit Charge HR, and accuracy of physical activity measures were evaluated relative to research-grade measures taken during a combination of 14 standardized laboratory- and field-based assessments of sitting, stationary cycling, treadmill walking or jogging, stair walking, outdoor walking, and agility drills. Accuracy of sleep measures were evaluated relative to polysomnography (PSG) in 26 boys and girls during an at-home unattended PSG overnight recording. The primary analyses included assessment of the agreement (biases) between measures using the Bland-Altman method, and epoch-by-epoch (EBE) analyses on a minute-by-minute basis.

Results: Fitbit Charge HR underestimated steps (~11.8 steps per minute), heart rate (~3.58 bpm), and metabolic equivalents (~0.55 METs per minute) and overestimated energy expenditure (~0.34 kcal per minute) relative to research-grade measures (p< 0.05). The device showed an overall accuracy of 84.8% for classifying moderate and vigorous physical activity (MVPA) and sedentary and light physical activity (SLPA) (sensitivity MVPA: 85.4%; specificity SLPA: 83.1%). Mean estimates of bias for measuring total sleep time, wake after sleep onset, and heart rate during sleep were 14 min, 9 min, and 1.06 bpm, respectively, with 95.8% sensitivity in classifying sleep and 56.3% specificity in classifying wake epochs.

Conclusions: Fitbit Charge HR had adequate sensitivity in classifying moderate and vigorous intensity physical activity and sleep, but had limitations in detecting wake, and was more accurate in detecting heart rate during sleep than during exercise, in healthy children. Further research is needed to understand potential challenges and limitations of these consumer devices.

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1. Bland-Altman plots for average steps (A), heart rate (B), energy expenditure (kcal) (C) and METs (D) per minute.

The central dotted line represents the Bland-Altman biases; the thin dotted lines represent the Bland-Altman agreement limits.

Fig 2. Bland-Altman plots for Total Sleep Time (TST), Sleep Onset Latency (SOL), and Wake After Sleep Onset (WASO).

The central dotted lines represent the Bland-Altman biases; the thin dotted lines represent the Bland-Altman agreement limits. *PSG is considered the gold standard for sleep assessment, therefore, mean bias was plotted against the PSG measurement alone and not the average of measures from PSG and the Fitbit Charge HR.

Fig 3. Bland-Altman plots for nocturnal Heart Rate (HR).

The thick dotted lines represent the Bland-Altman bias; the thin dotted lines represent the Bland-Altman upper and lower agreement limits.