Validation of smartphone step count algorithm used in STARFISH smartphone application

BACKGROUND: Smartphone sensors are underutilised in rehabilitation. OBJECTIVE: To validate the step count algorithm used in the STARFISH smartphone application. METHODS: Twenty-two healthy adults (8 male, 14 female) walked on a treadmill for 5 minutes at 0.44, 0.67, 0.90 and 1.33 m⋅s-1 . Each wore an activPAL TM and four Samsung Galaxy S3TM smartphones, with the STARFISH application running, in: 1) a belt carrycase, 2) a trouser or skirt pocket), 3a) a handbag on shoulder for females or 3b) shirt pocket for males and 4) an upper arm strap. Step counts of the STARFISH application and the activPALTM were compared at corresponding speeds and Bland-Altman statistics used to assess level of agreement (LOA). RESULTS: The LOA between the STARFISH application and activPALTM varied across the four speeds and positions, but improved as speed increased. The LOA ranged from 105–177% at 0.44 m⋅s-1; 50–98% at 0.67 m⋅s-1; 19–67% at 0.9 m⋅s-1 and 8–53% at 1.33 m⋅s-1. The best LOAs were at 1.33 m⋅s-1 in the shirt pocket (8%) and upper arm strap (12%) positions. CONCLUSIONS: Step counts measured by the STARFISH smartphone application are valid in most body positions especially at walking speeds of 0.9 m⋅s-1 and above.