title: Validity of the iPhone M7 motion co-processor as a pedometer for able-bodied ambulation.
abstract: Physical activity benefits for disease prevention are well-established. Smartphones offer a convenient platform for community-based step count estimation to monitor and encourage physical activity. Accuracy is dependent on hardware-software platforms, creating a recurring challenge for validation, but the Apple iPhone® M7 motion co-processor provides a standardised method that helps address this issue. Validity of the M7 to record step count for level-ground, able-bodied walking at three self-selected speeds, and agreement with the StepWatchTMwas assessed. Steps were measured concurrently with the iPhone® (custom application to extract step count), StepWatchTMand manual count. Agreement between iPhone® and manual/StepWatchTMcount was estimated through Pearson correlation and Bland-Altman analyses. Data from 20 participants suggested that iPhone® step count correlations with manual and StepWatchTMwere strong for customary (1.3 ± 0.1 m/s) and fast (1.8 ± 0.2 m/s) speeds, but weak for the slow (1.0 ± 0.1 m/s) speed. Mean absolute error (manual-iPhone®) was 21%, 8% and 4% for the slow, customary and fast speeds, respectively. The M7 accurately records step count during customary and fast walking speeds, but is prone to considerable inaccuracies at slow speeds which has important implications for certain patient groups. The iPhone® may be a suitable alternative to the StepWatchTMfor only faster walking speeds.
authors.affiliation: a Department of Physical Medicine & Rehabilitation, Feinberg School of Medicine , Northwestern University Prosthetics-Orthotics Center , Chicago , IL , USA.|b Department of Veterans Affairs , Jesse Brown VA Medical Center , Chicago , IL , USA.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Major
authors.affiliation: a Department of Physical Medicine & Rehabilitation, Feinberg School of Medicine , Northwestern University Prosthetics-Orthotics Center , Chicago , IL , USA.
authors.forename: Micah
authors.initials: M
authors.lastname: Alford
mesh_terms: D056044:Actigraphy / Q000379:methods* / Q000592:standards; D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D063731:Mobile Applications; D015203:Reproducibility of Results; D000068997:Smartphone; D016138:Walking / Q000502:physiology*; D055815:Young Adult
keywords: Physical activity; accelerometer; smartphone; walking