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What is the difference between the Energy Expenditure Algorithms?
What is the difference between the Energy Expenditure Algorithms?
Last Updated: Feb 08, 2012
Views: 1788
Five physical activity (PA) energy expenditure algorithm options are available to users:
- Work-Energy Theorem. This formula utilizes the physics equivalent of energy
kcals=Counts×0.0000191×Mass
where
kcals=Total Calories for a Single Epoch
Counts=Count Level for a Single Epoch
Mass=Weight in Kg
- The Freedson Equation. Developed by Dr. Patty Freedson in 1997 in the research publcation Calibration of the Computer Science and Applications, Inc. Accelerometer, this equation is only accurate above 1951 counts for adults.
kcals=Scale×(0.00094×Counts+(0.1346×Mass-7.37418))
[for Counts≥(1952×Scale)]
where
Scale=(Epoch Period in Seconds÷60)
- Combination (Work Energy and Freedson). When selected, the combination option automatically uses the Work-Energy Theorem to calculate caloric expenditure below 1951 counts and the Freedson Equation to calculate energy expenditure above 1952 counts.
kcals={(Work/Energy Theorem for Counts<1952; Freedson Equation for Counts≥1952)
- Vector Magnitude. This option uses all three axes (if data is collected on all three axes) to estimate energy expenditure. The Vector Magnitude calculation is only valid if the epoch counts exceed the Scale×2453. This formula was validated by Freedson in 2010. See http://www.theactigraph.com/article/research-database/validation/calibration-of-the-actigraph-gt3x-activity-monitor/ for more details.
kcals = Scale×[(0.00097×VectorMagnitude(axis1,axis2,axis3))+(0.08793×Mass)]-5.01582 for Counts>Scale×2453
where
Scale=(Epoch Period in Seconds÷60)
- Vector Magnitude Combination. This option combines the Vector Magnitude formula above with the Work-Energy theorum when 60 second epoch counts are less than 2453.
kcals = Scale×[(0.00097×VectorMagnitude(axis1,axis2,axis3))+(0.08793×Mass)]-5.01582 for Counts>Scale×2453
kCals = Counts×0.0000191×Mass for Counts ≤ Scale×2453
where
Scale=(Epoch Period in Seconds÷60)
Important: Energy Expenditure calculations are only accurate for adults, age 19years and up.
This FAQ Applies To:
GT1M Device
GT3X Device
GT3X+ Device
ActiLife Software
ActiLife6 Software
© 2012 ActiGraph, LLC. All Rights Reserved.