Wrist accelerometry for physical activity measurement in individuals with spinal cord injury – a need for individually calibrated cut-points

Publication date: Available online 6 December 2017
Source:Archives of Physical Medicine and Rehabilitation
Author(s): Laura A. McCracken, Jasmin K. Ma, Christine Voss, Franco H.N. Chan, Kathleen A. Martin Ginis, Christopher R. West
ObjectiveTo create and compare individual and group-based cut-points for wrist-accelerometry that corresponds to moderate-to-vigorous physical activity (MVPA) in people with spinal cord injury (SCI).DesignParticipants completed a graded treadmill-wheeling test while being assessed for oxygen consumption, wrist-acceleration vector magnitude, and spoke acceleration. Oxygen consumption was converted to SCI metabolic equivalents (SCI METS) and linear regression was applied to determine an individualized vector magnitude cut-point (counts per minute, VM-CPM) corresponding with MVPA (≥3 SCI METS). Multilevel linear regression was applied to determine a group MVPA cut-point. Participants then completed a 6-day monitoring period while wearing the accelerometers.SettingA local SCI research centre.ParticipantsTwenty manual wheelchair users (30-64yrs, C5-L1) with chronic (>1 year) SCI.InterventionsNot applicable.Main outcome measuresMean total daily MVPA, wheeled MVPA, and non-wheeled MVPA were calculated using both the individual and group cut-points. Agreement on measures of min/day of MVPA between the individual and group mean cut-point method was compared using Bland-Altman plots.ResultsIndividual cut-points for MVPA ranged from 6040 to 21540 VM-CPM, with a group cut-point of 11652 (CI 7395 – 15909). For total daily MVPA, Bland-Altman analysis revealed a bias of 0.22 ± 33.0 minutes, with 95% limits of agreement from -64.5 to 64.9 minutes, suggesting a large discrepancy between total MVPA calculated from individual and group-mean cut-points.ConclusionsIndividual calibration of wrist-worn accelerometry is recommended for effective habitual PA monitoring in this population.



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