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

Abstract

Objective: This study aimed to assess the validity and reliability of the 3DNX triaxial accelerometer in a laboratory and mechanical setting. Methods: 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 À1 ) 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 À1 ). Results: Experiment 1: CV intra ranged from 0.0 to 8.9% in all axes. The absolute bias ± 95% LoA values were all below four counts 5 s À1 . CV inter 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 R 2 value of 0.99 and a standard error of the estimate (SEE) of six counts 5 s À1 . Experiment 2: CV inter 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 À0.7% (P40.05)±12.4% and 0.4% (P40.05)±5.6%, respectively. The relationship between . VO 2 and 3DNX counts for walking and running was linear (R 2 ¼ 0.65, SEE ¼ 1.42 ml kg À1 min À1 ; R 2 ¼ 0.62, SEE ¼ 3.63 ml kg À1 min À1 ). Conclusion:The 3DNX accelerometer is a reliable and valid device for measuring acceleration in a mechanical setting and during human treadmill exercise.

Predicting Physical Activity Energy Expenditure in Manual Wheelchair Users

“…In our study, the ICC observed across testing conditions were high and concurred with those reported for other available accelerometers (18,26) and previous generations of ActiGraph (5). If interunit reliability is poor, then it becomes difficult to distinguish whether the variability in PA during free-living monitoring between subjects is solely attributed to variations in behavior or inherent to the accelerometer.…”

“…The weak relation of R s = 0.25 between 0.06g and 1.5g is well below that of most industry-standard PA monitoring accelerometers. The GENEA and 3DNX PAC outputs are both strongly related to acceleration during a mechanical setup, with correlations of r = 0.97 and r = 0.99, respectively (10,18). In the older 7164 model ActiGraph, Brage et al (5) unequivocally stated that count output is only proportional to acceleration if frequency is held constant, implying that some form of frequency-dependent filter exists.…”

“…The coefficient of variation (CV intra ) was calculated from the replicate 5-s epochs within each condition to assess intraunit reliability. This is a noteworthy distinction of our design compared with those of previous research in the field of intraunit reliability analyses, which tend to focus on within-unit, between-trial variability (18). However, we adopted an approach similar to that of Esliger and Tremblay (11) to remove any trial effects that may increase variability (i.e., more technological error).…”

Accelerometer-based measures in physical activity surveillance: current practices and issues

“…Accelerometer reliability is subject to technical (eg, inconsistencies in capturing signals and processing data) and human-related (eg, accidental altering of the position of device) sources of random error. Accelerometers demonstrated high intrainstrument and interinstrument reliability in mechanical laboratory settings, with coefficients of variation (CV) mostly below 5% and 10%, respectively,34–43 and when assessing structured activities in controlled laboratory conditions, with most intraclass correlation coefficients (ICCs) ranging from 0.60 to 0.90 36 42 44–48. Interinstrument reliability of accelerometers in free-living conditions ranged from mediocre for RT3 accelerometers (CV 9.8–39.8%)49 to relatively high for Actigraph 7164 and GT1M models (CV 0.9–15.5%) 49 50.…”

Five-minutes-to-twelve for implementation of early changes in dietary and lifestyle behaviour across Europe

“…This supplement contains many studies carried out to ensure the quality and rigour of measures included in the IDEFICS study. This measurement rigour has been applied to diet 8,9 and physical activity, [10][11][12] as well as to measurement of social and biological determinants [13][14][15] and health consequences. [16][17][18][19][20] Furthermore, the detailed description of both the strengths and limitations with regard to measurement selection and development is an important resource for dissemination, given its potential for shaping future studies.…”