Sciknow Publications Ltd. HC 2013, 1(1):5-8 Health Care DOI: 10.12966/hc.5.2.2013 'Attribution 3.0 Unported (CC BY 3.0) Validity and Reliability of Measuring Steps and Energy Expenditure with a Triaxial Accelerometer in Healthy Adults under Controlled Conditions Dirk Vissers 1,* , Nick Gebruers 1 , Johan Roeykens 2 , Steven Truijen 1 and Jan Gielen 1,2 1 Faculty of Medicine and Health Scences, University of Antwerp, Belgium 2 S.P.O.R.T.S., Antwerp University Hospital, Belgium *Corresponding author (dirk.vissers@ua.ac.be) Abstract Purpose: To determine the validity and test-retest reliability of a triaxial accelerometer in measuring steps and estimating energy expenditure in healthy adults. Method: 20 volunteers walked 3 times for 10 minutes on a treadmill following a standardized protocol. Data of the accelerometer were compared to hand tally counted steps and to breath by breath analysis of respiratory variables. Bland-Altman plots and an intra-class correlation coefficients were used to determine validity and reliability. Results: Accelerometers generated valid results at 5km/h but not at 3km/h. At 5 km/h the lanyard and belt positions were more valid than the pocket positions. The test-retest reliability was good to excellent for steps (ICC range .78 - .92) and moderate to good for energy expenditure (ICC range .64 - .87). Conclusions: The accelerometer generated valid results for the number of steps at 5 km/h with a coefficient of variation of 1-1.6% but overestimated energy expenditure. Keywords - Physical activity, monitoring, accelerometry, validity 1. Introduction The importance of physical activity in relationship to overall health status and mortality prevention is well established (Fitzsimons, Baker, Gray, Nimmo, & Mutrie., 2012; Woodcock, Franco, Orsini, & Roberts, 2011 ). Accelerometry is a technology based upon the measurement of accelerations which can be used as a measurement of physical activity (Chen & Bassett, 2005). When medical practioners, dieticians or physiotherapists want to use accelerometers to measure the activity of daily life these accelerometers need to be valid and reliable and easy to use by patients or other users. The Yorbody physical activity monitor is a triaxial accelerometer that integrates acceleration from three planes to yield a vector magnitude, requiring no calibration. The accelerometer detects total movements and total duration of the movements per day and estimates energy expenditure thru acceleration per movement for each period of active gait in real time. The aim of the current study is to determine the validity and reliability of the Yorbody accelerometer in measuring steps and estimating energy expenditure conditions. 2. Methods Twenty healthy participants were consecutively recruited from September 2011 to October 2011. Volunteers were included after informed consent, based upon the following criteria: 1) age between 20-60y, 2) healthy and therefore able to walk at 5km/h. Volunteers were excluded if 1) diabetes was diagnosed, 2) any disease or injury was present that hampered a normal walking and 3) presence of endocrine disturbances that could influence energy expenditure. The protocol was approved by the ethical committee of the University Hospital of Antwerp (N B300201 111940). 3. Protocol The participants walked three times for 10 minutes on a