NO FULL TEXT AVAILABLE. This thesis contains 3rd party copyright material. ----- There has been substantial growth in the use of Global Positioning System (GPS) technology for monitoring athlete movement demands in team sports, particularly Australian football. However, it is unknown whether current GPS models are capable of precisely measuring athlete movement demands. In addition, the optimal application of the information provided from GPS units by sporting practitioners to obtain a competitive advantage over the competition requires a comprehensive investigation. The overall aim of this study was two-fold: firstly, to determine whether 5 Hz and 10 Hz GPS units provided valid and reliable measures of athlete movement demands; secondly, whether there were relationships between athlete movement demands, energy cost of match-play, metabolic power outputs, match events, levels of competition, match performance and match fatigue. Seven separate studies were conducted and reported in seven manuscripts. In studies 1 and 2 participants completed a team sport simulation circuit whilst wearing 5 Hz, 10 Hz Catapult and 15 Hz GPSports GPS units. The results revealed that the 10 Hz GPS units were more valid and reliable for measuring athlete movement demands than the 5 Hz and 15 Hz GPS units. Despite the good to moderate levels of reliability for total distance covered, speed and the distance covered, time spent and number of efforts performed at low and high speed running (<20 km h⁻¹), it was evident that caution is still warranted when analysing movement demands performed at very high-speed running (>20 km h⁻¹). Studies 3 and 4 developed and assessed a standardised set of acceleration zones to determine whether 5 Hz and 10 Hz GPS units were able to reliably measure the distance covered, time spent and number of efforts performed at these zones. These standardised acceleration zones were also used to report on the acceleration and deceleration profiles of Australian football athletes and to examine differences between playing positions. The findings demonstrated that 5 Hz and 10 Hz GPS units provide reliable measures of the distance covered and time spent at the acceleration and deceleration zones analysed. It was evident that nomadic players and fixed defenders completed more accelerations and declarations in a match than fixed forwards and ruckman. Study 5 examined whether any differences existed in the movement demands, energy cost of match-play and metabolic power outputs of elite and sub-elite Australian football players. The findings revealed that whilst elite athletes had a lower match duration, they completed more high-speed running, more high acceleration and deceleration efforts, and had a higher work rate than the sub-elite athletes. In studies 6 and 7 the relationship between athlete movement demands, energy costs, metabolic power outputs, match events and match performance (coach’s rating) and fatigue (rating of perceived exertion) were examined. These studies revealed that the high calibre and high load players completed more high intensity efforts and had a higher work rate than the low calibre and low load players. Overall this research has demonstrated that coaches and conditioning staff can use GPS units to measure movement demands and that updates in firmware and sampling rates have further improved the validity and reliability of GPS units. The development of standardised acceleration zones that are capable of distinguishing between playing positions and providing further insight into the physical demands placed on team sport athletes is also advantageous for practitioners and researchers. It will enable comprehensive insight into the movement profiles of athletes and comparisons to be made between research studies that adopt these standardised zones. The in-depth analysis of athlete movement demands, energy costs, metabolic power outputs and match events identified the importance of involving small-sided games to provide both a physical and skill stimuli. Similarly, these studies identified the importance of measuring the energy cost and metabolic power outputs of athletes to comprehensively understand the physical demands placed on team sport athletes and understand their work rates.