Providing a Basis for Harmonization of Accelerometer-Assessed Physical Activity Outcomes Across Epidemiological Datasets

Abstract

Introduction: To capitalize on the increasing availability of accelerometry data for epidemiological research it is desirable to compare and/or pool data from surveys worldwide. This study aimed to establish whether free-living physical activity outcomes can be considered equivalent between three research-grade accelerometer brands worn on the dominant and non-dominant wrist. Of prime interest were the average acceleration (ACC) and the intensity gradient (IG). These two metrics describe the volume and intensity of the complete activity profile; further, they are comparable across populations making them ideal for comparing and/or pooling activity data. Methods: Forty-eight adults wore a GENEActiv, Axivity, and ActiGraph on both wrists for up to 7-days. Data were processed using open-source software (GGIR) to generate physical activity outcomes, including ACC and IG. Agreement was assessed using pairwise 95% equivalence tests (±10% equivalence zone) and intra-class correlation coefficients (ICC). Results: ACC was equivalent between brands when measured at the non-dominant wrist (ICC ≥ 0.93), but approximately 10% higher when measured at the dominant wrist (GENEActiv and Axivity only, ICC ≥ 0.83). The IG was equivalent irrespective of monitor brand or wrist (ICC ≥ 0.88). After adjusting ACC measured at the dominant wrist by −10% (GENEActiv and Axivity only), ACC was also within (or marginally outside) the 10% equivalence zone for all monitor pairings. Conclusion: If average acceleration is decreased by 10% for studies deploying monitors on the dominant wrist (GENEActiv and Axivity only), ACC and IG may be suitable for comparing and/or collating physical activity outcomes across accelerometer datasets, regardless of monitor brand and wrist.

A data-driven, meaningful, easy to interpret, population-independent accelerometer outcome variable for global surveillance

“…The following metrics were generated and averaged across all valid days: average acceleration; intensity gradient (intensity distribution 23 ); acceleration above which a person's most active X minutes (MXACC) are accumulated: M60ACC (mg); M30ACC (mg), M2ACC (mg), (GGIR qlevels (0,24 hours): 1380/1440, 1410/1440 and 1438/1440). As acceleration measured at the dominant wrist is approximately 10% higher than the non-dominant 24 , magnitudes of M60ACC, M30ACC and M2ACC were reduced by 10% for dominant wrist placement (pre-and post-menopausal women).…”

“…All accelerometer files for the pre-and post-menopausal women from UK Biobank meeting the criteria of Stiles et al 16 were available and included (see Stiles et al 18 for details). 24 . ** zBMI: BMI expressed in z-scores for sex and age according to reference curves for the UK 27 .…”

“…The acceleration magnitudes tended to be higher for the pre-menopausal women who wore the Axivity on their dominant wrist than for the slightly younger office workers who wore the ActiGraph on their non-dominant wrist. While this may be due to the sedentary nature of the office job, it could reflect the non-representative nature of the samples, indicate that the -10% reduction in acceleration for dominant wrist placement 24 was insufficient, and/or that there were differences between the ActiGraph and the Axivity. While raw data from the GENEActiv and Axivity accelerometers compare well 24 , 'raw' data from the ActiGraph GT9X is passed through a filter that suppresses higher intensity accelerations.…”

“…While this may be due to the sedentary nature of the office job, it could reflect the non-representative nature of the samples, indicate that the -10% reduction in acceleration for dominant wrist placement 24 was insufficient, and/or that there were differences between the ActiGraph and the Axivity. While raw data from the GENEActiv and Axivity accelerometers compare well 24 , 'raw' data from the ActiGraph GT9X is passed through a filter that suppresses higher intensity accelerations. The accelerometer sampling frequency and epoch differed between some studies.…”

“…In addition, the proportion of pre-and post-menopausal women meeting the recently proposed accelerometer-driven guide of 2 min high-intensity activity associated with bone health 16 was calculated. The thresholds (>1000 mg (medium run) pre-menopausal, > 750 mg, post-menopausal (slow run)) were generated using dominant wrist data 16 , so are adjusted by -10% 24 .…”