INTRODUCTION: Traditionally, development and testing of materials or equipment has been based on repeated measurements with resources including timing cells or wind tunnels. Similarly, the analysis of athletes' performance has relied on techniques such as measuring race segments (chronometry) and video recordings. These methods, however, appear vulnerable to changing meteorological conditions and the difficulty of replicating the posture and movements of test subjects from one trial to the next. Furthermore, chronometry has a discrete character while researchers, coaches, and athletes are interested in observing certain phenomena continuously. Satellite-based positioning offers continuous observation of the athletes' trajectory and velocity and has already proven its effectiveness in many sports, including skiing (Waegli and Skaloud, Spring 2007). However, the fluctuation in accuracy often discouraged the regular employment of the technology. Therefore, quality indicators are introduced in order to qualify the statistical relevance of the satellite data. METHOD: An athlete was equipped with a low-cost, single-frequency (L1) GPS receiver as well as a dual-frequency reference receiver yielding sub-decimeter accuracy. First, the Position and velocity accuracy of the low-cost receiver were assessed. Next, the location of the timing gates was determined with centimeter precision, which permitted the assessment of timing based on GPS trajectories with respect to traditional chronometry. RESULTS: The selected low-cost L1 GPS receiver combined with the appropriate differential GPS algorithms offers accuracies better than 0.5m for position and 0.2m/s for velocity (1o). Quality indicators show clearly when the observed phenomenon is statistically significant. Furthermore, timing based on GPS trajectories proves to be as accurate as chronometry based on timing cells. DISCUSSION: For economical reasons the tracking of a large number of athletes requires the use of low-cost GPS receivers. The current pricing of dual-frequency GNSS receivers restricts their use to a few athletes and applications with high accuracy requirements. The continuous observation of the trajectory certainly has many advantages: the comparisons can be made over smaller sections (for example gate-to-gate analysis) and can include topological aspects such as finding an ideal trajectory by comparing different tracks. Furthermore, other parameters related to a defined section of the track (heart rate, velocity etc.) can be compared rigorously. CONCLUSION: GPS positioning and timing present an interesting alternative to traditional methods applied for material testing and athletes' performance analysis. The presented low-cost System offers additional flexibility through continuous and accurate observation of an athlete's trajectory.
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