Reliability and validity of a GPS-enabled iPhoneTM “app” to measure physical activity

Abstract This study assessed the validity and reliability of an iPhoneTM “app” and two sport-specific global positioning system (GPS) units to monitor distance, intensity and contextual physical activity. Forty (23 female, 17 male) 18–55-year-olds completed two trials of six laps around a 400-m athletics track wearing GPSports ProTM and WiSpiTM units (5 and 1 Hz) and an iPhoneTM with a Motion X GPSTM “app” that used the inbuilt iPhoneTM location services application programming interface to obtain its sampling rate (which is likely to be ≤1 Hz). Overall, the statistical agreement, assessed using t-tests and Bland–Altman plots, indicated an underestimation of the known track distance (2.400 km) and average speed by the Motion X GPSTM “app” and GPSports ProTM while the GPSports WiSpiTM device overestimated these outcomes. There was a ≤3% variation between trials for distance and average speed when measured by any of the GPS devices. Thus, the smartphone “app” trialled could be considered as an accessible alternative to provide high-quality contextualised data to enable ubiquitous monitoring and modification of programmes to ensure appropriate intensity and type of physical activity is prescribed and more importantly adhered to.