Assessment of Daily Physical Activity Using Vector Magnitude of Actigraph Tri-axial Accelerometer

Objective:To determine the VM energy expenditure prediction equations and VM thresholds of Actigraph tri-axial accelerometer for Chinese young adults, and aim to provide evidence for the valid application of Actigraph tri-axial accelerometer.Methods:Participants simultaneously wore Cosmed K4b2 portable indirect calorimetry system and Actigraph GT3X accelerometer to assess their physical activities, indirect calorimetry was used as the criterion measurement of energy expenditure.Subjects of development group (30 men and 30 women) performed activities including sitting, reading, cleaning desk, sweeping and 3speeds of overgroud walking and jogging (4km/h, 6km/h and 8km/h) , the data were used to develop VM energy expenditure prediction equations and VM thresholds.Data of the 4h daily physical activity of validation group (10 men and 10 women) were used to validate the equations and thresholds developed in this study and the counterparts already existed.Results:Two equations were developed (equation 1:kcal/min=0.000784*VM + 0.054*BM-1.947, equation 2:METs=0.000721*VM + 1.399) , two sets of VM thresholds of 3METs and 6METs were also established.The validation showed that there was no significant difference between the PAEE4h predicted by the VM equations developed in this study and the PAEE4h measured by indirect calorimetry, other VM equations significantly underestimated PAEE4h.The VM thresholds established by ROC curve were confirmed to be valid in measuring the time of LPA, MPA, VPA and MVPA, the error of other VM thresholds had statistical significance.Conclusion:VM was valid in assessing daily physical activity.The VM energy expenditure prediction equations developed in this study and the thresholds developed by ROC curve were suitable for the physical activity assessment of Chinese young adults.