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Advances in global navigation satellite system (GNSS) technology have resulted in
smaller and more accurate GNSS receivers, which have become increasingly suitable
for calculating instantaneous performance parameters during sports competitions,
for example by providing the difference in time between athletes at any location
along a course. This study investigated the accuracy of three commercially available
GNSS receivers directed at the sports market and evaluated their applicability for
time analysis in endurance racing sports. The receivers evaluated were a 1 Hz
wrist-worn standalone receiver (Garmin Forerunner 920XT, Gar-920XT), a 10 Hz
standalone receiver (Catapult Optimeye S5, Cat-S5), and a 10 Hz differential receiver
(ZXY-Go). They were validated against a geodetic, multi-frequency receiver providing
differential position solutions (accuracy < 5 cm). Six volunteers skied four laps on
a 3.05 km track prepared for cross-country skiing, with all four GNSS receivers
measuring simultaneously. Deviations in position (horizontal plane, vertical, direction
of travel) and speed (horizontal plane and direction of travel) were calculated. In
addition, the positions of all receivers were mapped onto a mapping trajectory along
the ski track, and a time analysis of all 276 possible pairs of laps was performed.
Specifically, the time difference between any two skiers for each integer meter along
the track was calculated. ZXY-Go, CAT-S5, and GAR-920XT had horizontal plane
position errors of 2.09, 1.04, and 5.29 m (third quartile, Q3), and vertical precision
2.71, 3.89, and 13.35 m (interquartile range, IQR), respectively. The precision in the
horizontal plane speed was 0.038, 0.072, and 0.66 m s−1
(IQR) and the time analysis
precision was 0.30, 0.13, and 0.68 s (IQR) for ZXY-Go, Cat-S5, and Gar-920XT,
respectively. However, the error was inversely related to skiing speed, implying that
for the low speeds typically attained during uphill skiing, substantially larger errors
can occur. Specifically, at 2.0 m s−1
the Q3 was 0.96, 0.36, and 1.90 s for
ZXY-Go, Cat-S5, and Gar-920XT, respectively. In summary, the differential (ZXY-Go) and 10 Hz standalone (Cat-S5) receivers performed substantially better than the wrist-worn
receiver (Gar-920XT) in terms of horizontal position and horizontal speed calculations.
However, all receivers produced sub-second accuracy in the time analysis, except at
very low skiing speeds.