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Reliability and validity of the 3DNX accelerometer during mechanical and human treadmill exercise testing



This study aimed to assess the validity and reliability of the 3DNX triaxial accelerometer in a laboratory and mechanical setting.


Experiment 1: A total of 10 units were fixed to a Multi-axis shaker table. A schedule comprising a range of accelerations was repeated on two occasions along each of the three measurement axes. Experiment 2: A total of 11 recreationally active individuals completed a treadmill protocol (4–20 km hr−1) on two occasions. Two 3DNX accelerometers were secured to the lower back, logging data every 5 s. Oxygen uptake was measured using the Douglas Bag technique. Reliability inter- and intra-units were assessed using a combination of limits of agreement (LoA), coefficient of variation (CV) and intra-class correlation coefficient (ICC). Validity was assessed using simple linear regression. All data are expressed in counts per 5 s (counts 5 s−1).


Experiment 1: CVintra ranged from 0.0 to 8.9% in all axes. The absolute bias±95% LoA values were all below four counts 5 s−1. CVinter did not rise above 4.5%. ICCs were 1.0 for all stages in all axes. The relationship between 3DNX counts and acceleration yielded an R2 value of 0.99 and a standard error of the estimate (SEE) of six counts 5 s−1. Experiment 2: CVinter ranged from 7.7 to 16.0% for trial 1 and from 7.7 to 16.2% for trial 2. ICCs between units ranged from 0.95 to 1.00 for trial 1 and from 0.90 to 0.99 for trial 2. Mean ratio bias±95% LoA values for intra-unit and inter-unit reliability were −0.7% (P>0.05)±12.4% and 0.4% (P>0.05)±5.6%, respectively. The relationship between O2 and 3DNX counts for walking and running was linear (R2=0.65, SEE=1.42 ml kg−1 min−1; R2=0.62, SEE=3.63 ml kg−1 min−1).


The 3DNX accelerometer is a reliable and valid device for measuring acceleration in a mechanical setting and during human treadmill exercise.

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We thank Professor Andrew Plummer, Mr Bernard Roe and the mechanical engineering department at the University of Bath for the use of the MAST rig and for their technical support. This study was conducted as part of the IDEFICS study ( We gratefully acknowledge the financial support of the European Community within the Sixth RTD Framework Programme under Contract No. 016181 (FOOD). All authors have received grant support from Optimal Performance Ltd.

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Correspondence to F E Horner.

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MR is a director of BioTel Ltd and has declared equity ownership/stock options with BioTel Ltd and Optimal Performance Ltd. The remaining authors declare no conflict of interest.

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Horner, F., Rayson, M., Bilzon, J. et al. Reliability and validity of the 3DNX accelerometer during mechanical and human treadmill exercise testing. Int J Obes 35 (Suppl 1), S88–S97 (2011).

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