Time motion analysis and GPS
To understand the demands of rugby, the game must be broken down into movements. For example, walking is going to have a much different physical stress compared to running but both occur in the game of rugby. Time motion analysis is a way of using non-invasive methods such as video-tracking to quantify the amount of time players spend in the different types of movement. This is a very useful way of analysing the movements of players and thus getting a better understanding of the movement and physical demands placed on the player during a game.
While time-motion analysis describes the main physical activities and most frequent activities that take place during a game, it does not describe the extent of physical force applied during contact. For example, time-motion analysis does not quantify the impact of being tackled or tackling nor the impact and force generated during other intense physical activities such as scrummaging, rucking and mauling. The efficiency of movement is also not described. The speed of changing direction or the rate of acceleration and deceleration and the running patterns used are not described using traditional video based time-motion analyses.
The development of GPS technology in sport has started to address the issues with traditional time-motion analysis. Global positioning system (GPS) is a satellite-based navigational technology and this technology allows three-dimensional movement of a player to be tracked over time in a range of different environments. GPS is increasingly being used in team sports and especially rugby to provide real-time analysis of the movements during a game or training.
By measuring player movements, GPS can estimate levels of physical stress and exertion, examine the workload at different positions, and assess game intensities. From its introduction, GPS has been used to measure basic components of player movement patterns, speed and distance travelled, and the number of accelerations and decelerations. Updates to GPS technology have allowed the measurement of physical contacts and collisions (Cummins et al, 2013).