Accuracy of GPS sport watches in measuring distance in an ultramarathon running race

Abstract

Purpose The aim of the study was to determine the accuracy of various global positioning system (GPS) sport watches in measuring distance throughout a 56 km running race. Methods The measured distance between timing mats was compared to the reported distance of GPS devices at the 2017 Two Oceans Marathon. Runners (n = 255) were divided into eight different categories based on GPS sport watch brand and model. The difference between distance measured by GPS and race markers was represented in metres (m) and as a relative error (%). Results The Garmin Fenix and cell phone categories had higher errors in measuring distance from the 16 km to finish (56 km) point compared to all other devices, except for activity watches. Conclusions The GPS sport watches in this study have an accuracy of 0.6 ± 0.3% to 1.9 ± 1.5% (median ± interquartile range) in reporting distance covered. This indicates that GPS sport watches are a valid and feasible method for sport scientists and coaches to measure performance and track training load. However, the small error associated with each brand needs to be considered when data are interpreted.