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Accuracy of Physical Activity Monitors in Pregnant Women


Medicine & Science in Sports & Exercise: June 2011 - Volume 43 - Issue 6 - p 1100-1105
doi: 10.1249/MSS.0b013e3182058883
Applied Sciences

Purpose: To determine the step count accuracy of three pedometers and one accelerometer in pregnant women during treadmill walking.

Methods: Participants were 30 women in the second or third trimester (20-34 wk) who were screened for pregnancy-related risk factors. Each participant was fitted with a belt containing three physical activity monitors: Yamax Digiwalker SW-200 (DW), New Lifestyles NL 2000 (NL), and GT3X ActiGraph accelerometer (ACT). The Omron HJ-720ITC (HJ) was placed in the pants' front pocket. Participants walked at 54, 67, 80, and 94 m·min−1 for 2 min each. Actual steps were determined by an investigator using a hand-tally counter. The mean percent of steps recorded was calculated for each device at each speed and compared. Pearson correlations were used to determine the effect of body mass index and tilt angle on pedometer accuracy.

Results: There was a significant interaction between speed and device (F 9,20 = 7.574, P < 0.001). Across all speeds, the NL and HJ had the lowest error. The ACT and DW underestimated the actual steps taken, particularly at the slower walking speeds. At 54 m·min−1, the ACT averaged 77.5% of steps and the DW averaged 56.9% of steps. Significant differences in the mean percent of steps recorded were found between devices at all speeds. Body mass index was only significantly correlated with percent of steps recorded by the NL, and there were no significant correlations between steps recorded and tilt angle.

Conclusions: In pregnant women, the ACT and DW had more error than the NL and HJ. On the basis of these results, the NL and HJ should be considered for use in further research studies and physical activity programs that focus on walking during pregnancy.

The University of Tennessee, Knoxville, TN

Address for correspondence: Dawn P. Coe, Ph.D., Department of Kinesiology, Recreation, and Sport Studies, 338 HPER, 1914 Andy Holt Ave., Knoxville, TN 37996; E-mail:

Submitted for publication May 2010.

Accepted for publication October 2010.

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©2011The American College of Sports Medicine