Validity of the Garmin Vivofit Jr. to Measure Physical Activity During a Youth After-School Program

Purpose: The purpose of this study was to evaluate the validity of the step count and Active Minutes features of the Garmin Vivofit Jr. 2 consumer activity monitor. Methods: Participants included 35 students (age 8–11) enrolled in an after-school physical activity (PA) and nutrition program. Participants wore an ActiGraph GT3x+ monitor on their waist and the Vivofit monitor on their wrist during the PA portion of the program. Data were collected across multiple sessions, resulting in 158 unique pairs of data. Pearson correlation, mean absolute percent error, and equivalence testing were performed to compare step count and minutes of activity (Vivofit Active Minutes vs ActiGraph moderate to vigorous PA) between the two monitors. Results: Moderate correlations were found between the monitors for steps (r = .65) and minutes (r = .43). Mean absolute percent error was 26% for steps and 43% for minutes, suggesting that there were high amounts of individual error. Equivalence testing showed significant agreement between the monitors for steps (p = .046), but not for minutes (p = .98). Conclusion: The Garmin Vivofit Jr. 2 shows acceptable validity for measurement of steps at a group level in a field-based setting, although the amount of individual variability must be considered. The Vivofit Jr. 2 was not valid for measurement of minutes of activity.