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Predicting physical activity intensity using raw accelerometer signals in manual wheelchair users with spinal cord injury


Study design

Cross-sectional validation study.


The performance of previously published physical activity (PA) intensity cutoff thresholds based on proprietary ActiGraph counts for manual wheelchair users (MWUs) with spinal cord injury (SCI) was initially evaluated using an out-of-sample dataset of 60 individuals with SCI. Two types of PA intensity classification models based on raw accelerometer signals were developed and evaluated.


Research institutions in Pittsburgh PA, Birmingham AL, and Bronx NY.


Data were collected from 60 MWUs with SCI who followed a structured activity protocol while wearing an ActiGraph activity monitor on their dominant wrist and portable metabolic cart which measured criterion PA intensity. Data was used to assess published models as well as develop and assess custom models using recall, specificity, precision, as well as normalized Mathew’s correlation coefficient (nMCC).


All the models performed well for predicting sedentary vs non-sedentary activity, yielding an nMCC of 0.87–0.90. However, all models demonstrated inadequate performance for predicting moderate to vigorous PA (MVPA) with an nMCC of 0.76–0.82.


The mean absolute deviation (MAD) cutoff threshold yielded the best performance for predicting sedentary vs non-sedentary PA and may be used for tracking daily sedentary activity. None of the models displayed strong performance for MVPA vs non-MVPA. Future studies should investigate combining physiological measures with accelerometry to yield better prediction accuracies for MVPA.

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Fig. 1: ROC analysis of the ENMO feature for both sedentary vs non-sedentary, and MVPA vs non-MVPA cutoff thresholds.
Fig. 2: ROC analysis of the MAD feature for both sedentary vs non-sedentary, and MVPA vs non-MVPA cutoff thresholds.

Data availability

The datasets supporting this study are available on reasonable request from the corresponding author.


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This study was funded by the VA Rehabilitation Research & Development under Grant #1I01RX000971-01A. The content is solely the responsibility of the authors and does not represent the official views of the VA.

Author information




YJS was responsible for conducting data analysis, obtaining results, and writing the manuscript in its entirety. ALV was responsible for designing the protocol, screening potential participants, and performing data collection. ZH conducted feature development for the random forest machine learning model. Also assisted with model tuning and development. SK was responsible for designing the protocol, screening potential participants, and performing data collection. EH was responsible for designing the protocol, screening potential participants, and performing data collection. AS oversaw a subset of data collection, which included screening participants, initializing equipment, and organizing patient visits. Also provided guidance for manuscript development. DD provided guidance throughout the study including formulating the manuscript plan, supervising the literature search, data collection, data analysis, and result interpretation, as well as editing the manuscript.

Corresponding author

Correspondence to Dan Ding.

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The authors declare no competing interests.

Ethics approval

This study was approved by the US Department of Veterans Affairs (VA) Central Institutional Review Board and the local Institutional Review Boards at the VA Pittsburgh Healthcare System and the James J. Peters VA Medical Center, respectively. We certify that all applicable institutional and governmental regulations concerning the ethical use of human volunteers were followed during the course of this research.

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Shwetar, Y., Huang, Z., Veerubhotla, A. et al. Predicting physical activity intensity using raw accelerometer signals in manual wheelchair users with spinal cord injury. Spinal Cord (2021).

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