The Open Sports Medicine Journal

2014, 8 : 11-15
Published online 2014 April 24. DOI: 10.2174/1874387001408010011
Publisher ID: TOSMJ-8-11

Comparison of FitBit® Ultra to ActiGraph™ GT1M for Assessment of Physical Activity in Young Adults During Treadmill Walking

R.J. Gusmer , T.A. Bosch , A.N. Watkins , J.D. Ostrem and D.R. Dengel
School of Kinesiology, University of Minnesota, 1900 University Avenue SE, Minneapolis, MN 55455, USA.

ABSTRACT

Introduction:

Accelerometers are used to quantify energy expenditure in field research. The ActiGraph™ GT1M (ActiGraph™) is a commonly used accelerometer for research. The FitBit® Ultra (FitBit®) is a low-cost alternative to the ActiGraph™; however, there is limited research on the validity of this device.

Purpose:

The pilot study compares the FitBit® against the ActiGraph™ and metabolic cart for measurement of energy expenditure and step counts during treadmill walking.

Methods:

Thirty-two (25 female) adults, mean age 22±2 years, performed two thirty-minute phases of walking (slow and brisk) on a treadmill while concurrently wearing the FitBit® and the ActiGraph™. Energy expenditure estimates were compared against energy expenditure measured by a metabolic cart. The Pearson’s correlation and t-tests determine the linear association and similarity between the accelerometers.

Results:

Energy expenditure estimate is moderately correlated between the two accelerometers during slow walking (r=0.584, p=0.011) and strongly correlated during brisk walking (r=0.910, p<0.001). Step count is strongly correlated between the accelerometers during slow (r=0.974, p<0.001) and brisk (r=0.996, p<0.001) walking. The FitBit® significantly underestimated energy expenditure during brisk walking compared to metabolic cart data. There is no difference between the slow and brisk phases’ step counts using either accelerometer.

Conclusion:

The results of this pilot study suggest that the FitBit® and the ActiGraph™ can be used interchangeably to measure steps, but not to measure kilocalories. Furthermore, the FitBit® underestimates energy expenditure, compared to a metabolic cart, as exercise intensity increases. This limits its ability to accurately measure energy expenditure in active populations.

Keywords:

Accelerometer, Bland-Altman, exercise.