# Intermonitor Variability of Garmin Vivofit(r) Jr. Wristband
## 4 Discussion  
This study investigated the intraclass reliability between Garmin Vivofit\({}^{\text{\textregistered}}\) Jr. wristbands for determining the number of steps and minutes of PA in situations that may reflect everyday life situations in children. The Garmin Vivofit Jr. wristbands are specific for children aged 4-10 years [17; 35], compared to a very high volume of PA wristbands of different brands that are tailored to the adult population [36; 37]. It is therefore critical to undertake this analysis to determine the robustness of measuring PA in children using these devices, as the variability between monitors needs to be minimal to allow adequate between-subject and within-subject comparisons [24]. Thus, the most important finding of this study is that the wristbands show good intraclass reliability for ordering steps and minutes of PA, and are suitable for field-based research. It was not possible to compare overestimates or underestimates with the previous literature because of the lack of other studies evaluating the reliability or validity of this specific  
Figure 6: Scatterplot between wristbands using Passing and Balbok regression for the variable steps: (i) wristband 1 vs. 2; (ii) wristband 1 vs. 3; (iii) wristband 2 vs. 3; (iv) wristband 4 vs. 5; (v) wristband 4 vs. 6; and (vi) wristband 5 vs. 6. The black line represents the regression line, the shaded area is the confidence interval for 95% of the regression line, and the discontinuous gray line is the perfect regression line. model of wristbands, although some studies have performed intra-device validation, as in the case of accelerometry [24; 25]. It is interesting to highlight that, regarding PA, this wristband measures steps and minutes of MVPA, with encouraging data regarding its reliable measurement for young children [16; 17]; although technical details and manufacturers' algorithms are sometimes kept confidential [9; 17]. However, to our knowledge, this is the first study to evaluate intra-device variability in a wristband intended for children, a truly useful aspect when this device is being applied in a school setting and other environments where different participants are simultaneously engaged [18; 19]. Thus, in the intra-device study, the evaluated wristbands showed a very small overestimation of the number of steps between Wristband 1 and Wristband 3 (1%) and between Wristband 2 and Wristband 3 (4%). The closest existing data in the literature refers to the Garmin Vivofit model, which, in activities typical of daily life throughout the day, offered this overestimation at 12% [13]. However, our results are in agreement with those of another study in which the Fitbit Flex wristband was used throughout the day (3%) [38], whereas in other wristbands, such as the Polar Loop, a wide range of 8.9 and 28% was used [37]. Therefore, the possible estimation in this study was shown to be between only 1 and 4% compared to other wristbands that do so in a range between 11 and 37%, such as the Fitbit (21%), Huawei (19%), Asus (11%), and Polar (37%) [39]. Regarding the underestimation of step count, the percentages of variability were between 2 and 4% (between wristband 1 and wristband 2 (3%), wristband 4 and wristband 5 (2%), wristband 4 and wristband 6 (4%), and wristband 5 and wristband 6 (3%). Although there are no specific data with a model in the literature, these low values are in agreement with other models of the same gait that have assessed PA in daily life conditions, with similar values between 4 and 5% underestimation (Garmin Vivofit and Garmin Vivofit 1 (4%), Garmin Vivofit 3 (5%) [37; 40]). These data highlight those studies assessing step volume in early-age children using the Garmin Vivofit Jr. model are methodologically reliable. Moreover, these are essential data since the recommendations for daily step volume are approximately 10,000 steps in the adolescent and adult population [41], while these values increase to 13,000 steps in the case of younger ages [42; 43].