BACKGROUND Elite athletes and recreational sport people rely on the accuracy of global navigation satellite system (GNSS)–enabled sport watches to monitor and regulate training activities. However, there is a lack of scientific evidence regarding the accuracy of such measurement devices. OBJECTIVE The aim of the present study was to investigate the accuracy of the recorded distances obtained by eight commercially available sport watches by Apple, Coros, Garmin, Polar, and Suunto when assessed

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... different areas and at different speeds. Furthermore, potential factors that affect the measurement quality were evaluated. METHODS 3 x 12 measurements in an urban, forest, and track and field area, respectively, were obtained while walking, running, and cycling under various outdoor conditions. RESULTS The recorded distances ranged from 404.0 m to 4,296.9 m. For all the measurement areas combined, the recorded systematic biases (±limits of agreements) ranged between 3.7 (±195.6) m and -101.0 (±231.3) m, and the mean absolute percentage errors ranged from 3.2% to 6.1%. Only the GNSS receivers from Polar showed overall errors <5%. Generally, the recorded distances were significantly underestimated (all P values <.04) and less accurate in the urban and forest areas, whereas they were overestimated but with good accuracy in 6/8 sport watches in the track and field area. Furthermore, the data assessed during running induced significantly higher error rates in most devices compared to the walking and cycling activities. CONCLUSIONS The recorded distances might be underestimated by up to 9%. However, the use of all investigated sport watches can be recommended, especially for distance recordings in open areas.