Quantifying validity and reliability of GPS derived distances during simulated tennis movements
Tennis is a competitive sport attracting millions of players and fans worldwide. During a competition, the physical component crucially affects the final result of a match. In field sports such as soccer physical demand data are collected using the global positioning system (GPS). There is question regarding the validity and reliability of using GPS technology for court sports such as tennis. The purpose of this study is to determine the validity and reliability of GPS to determine distances covered during simulated tennis movements. This was done by comparing GPS recorded distances to distances determined with a calibrated trundle wheel. Two SPI HPU units were attached to the wheel Four different trials were performed to assess accuracy and reliability: distance trial (DIST), shuttle run trial (SHUT), change of direction trial (COD) and random movement trial (RAND). The latter three trials are performed on a tennis court and designed to mimic movements during a tennis match. Bland-Altman analysis showed that during all trails, there were small differences in the trundle wheel and GPS derived distances. Bias for the DIST, SHUT, COD and RAND trails were -0.02±0.10, -0.51±0.15, -0.24±0.19 and 0.28±0.20%, respectively. Root mean squared (RMS) errors for the four trials were 0.41±0.10, 1.28±0.10, 1.70±0.10 and 1.55±0.13%. Analysis of paired units showed a good reliability with mean bias and RMS errors <2%%. These results suggest that SPI HPU units are both accurate and reliable for simulated tennis movements. They can be confidently used to determine the physical demands of court sports like tennis.