Validity of Fitbit Inspire 2 in step count and distance measurement during treadmill walking

Background As technology evolves, the market for wearable physical activity monitors has expanded exponentially. As the user base of activity trackers grows, ensuring their accuracy and validity becomes increasingly crucial. However, research in this field remains limited. Methods This study evaluated the validity and accuracy of Fitbit in measuring step count and distance during standardised treadmill walking (5.5 km/h) for 30 minutes. Comparisons were made with the gold standard of manual step counting. ActiGraph data was collected and analysed simultaneously as a comparator. Results Thirty college students (16 males, 14 females) participated. Fitbit demonstrated excellent agreement with manually counted steps (intraclass correlation coefficients (ICCs) = 0.91, 95% CI: 0.81–0.96, p < 0.001). Overall Fitbit underestimated steps (mean absolute percentage error (MAPE) = 3.6 ± 0.03%) and distance travelled (MAPE = 10.5 ± 0.07%). Fitbit accuracy was higher in females (MAPE = 9.4 ± 0.07%) than males (MAPE = 11.4 ± 0.06%). A Bland-Altman plot between Fitbit and manual count presented less than 1% limit of agreement range (286.6 to −83.7). In contrast, ActiGraph lacked agreement and accuracy in step measurement in a controlled setting. Notably, gender differences may impact the accuracy in distance travelled but not in step counts recorded by Fitbit. Conclusions Our findings underscore the high validity and moderate-to-high accuracy of the Fitbit Inspire 2 in measuring step count relative to manual counting within controlled settings among young, healthy adults. However, Fitbit displayed low accuracy in measuring distance travelled compared to actual distances.