How far from the gold standard? Comparing the accuracy of a Local Position Measurement (LPM) system and a 15 Hz GPS to a laser for measuring acceleration and running speed during team sports

Purpose This study compared the validity and inter- and intra-unit reliability of local (LPM) and global (GPS) position measurement systems for measuring acceleration during team sports. Methods Devices were attached to a remote-controlled car and validated against a laser. Mean percentage biases (MPBs) of maximal acceleration (a(max)) and maximal running speed (v(max)) were used to measure validity. Mean between-device and mean within-device standard deviations of the percentage biases (bd-SDs and wd-SDs) of a(max) and v(max) were used to measure inter- and intra-unit reliability, respectively. Results Both systems tended to underestimate a(max) similarly (GPS: -61.8 to 3.5%; LPM: -53.9 to 9.6%). The MPBs of a(max) were lower in trials with unidirectional linear movements (GPS: -18.8 to 3.5%; LPM: -11.2 to 9.6%) than in trials with changes of direction (CODs; GPS: -61.8 to -21.1%; LPM: -53.9 to -35.3%). The MPBs of v(max) (GPS: -3.3 to -1.0%; LPM: -12.4 to 1.5%) were lower than those of a(max). The bd-SDs and the wd-SDs of a(max) were similar for both systems (bd-SDs: GPS: 2.8 to 12.0%; LPM 3.7 to 15.3%; wd-SDs: GPS: 3.7 to 28.4%; LPM: 5.3 to 27.2%), whereas GPS showed better bd-SDs of v(max) than LPM. Conclusion The accuracy depended strongly on the type of action measured, with CODs displaying particularly poor validity, indicating a challenge for quantifying training loads in team sports.

Automated summary

The study compared the validity and reliability of local and global position measurement systems for measuring acceleration during team sports. Both systems tended to underestimate maximal acceleration, especially during changes of direction. Global Positioning System (GPS) showed better reliability in measuring maximal running speed compared to Local Positioning Measurement (LPM).