Global Positioning System (GPS)
In the Pre-Level 1 modules, monitoring strategies for training load such as Rating of Perceived Exertion (RPE) and Wellness questionnaires were introduced, and it was shown how these are valuable, inexpensive, uncomplicated methods of assessing the training load. This section expands the topic of workload monitoring. The use of GPS is one such method that can be used to assess the demands of the sport and the loading placed on players during game and training time.
According to Hennessy and Jeffreys in 2018, GPS technology uses receivers and satellites to determine relatively exact positions of the receiving devices. The receiver calculates the amount of time it takes to receive a signal from a satellite and from this the position of the receiver can be determined. Once the receiver links with several orbiting satellites, a GPS receiver can provide a reasonably exact position and speed of the receiver device. In sporting environments, the GPS receiver device signal is often augmented with stationary ground-based receivers which can enhance the signal from the satellites and deliver a more accurate and reliable reading. Over time GPS technology in sport has evolved and the GPS receiver devices now also have other micro-electromechanical sensors built in such as gyroscopes and accelerometers. This additional technology allows for the quantification of metrics related to body impact, adding to the concept of workload monitoring. GPS technology has allowed for a greater understanding of the physical demands and workload of different team formations and positional profiling during match play, as well as training.
While GPS research provides excellent information on the movement and impact demands placed on players during both games and training, it is not a technology without issues. When using GPS data to monitor workload of their players, coaches must get valid and reliable readings from the GPS device. This means separating the noise or error from the actual signal in a GPS system. The rate at which the GPS devices sample per second is an important aspect for validity and reliability. Early GPS models used a sample rate of 1 Hz or 1 sample per second. This was then increased to 5 Hz, but these devices were shown to demonstrate poor validity and reliability when measuring high-speed efforts. Subsequently 10 Hz measurement devices were developed, which provided greater reliability and validity with the higher speed measurements. 15 Hz and even 18 Hz GPS devices have now been developed and these may provide greater accuracy of measurement especially above the high-speed thresholds.
According to Malone and colleagues in 2020, coaches are encouraged to look at the GPS system they have access to and examine its validity and reliability. The importance of this can be highlighted by the following example. If a coach is using a certain metric from GPS to monitor workload, they would be following the changes in this metric on a day to day or week to week basis and using the information to make training and programming decisions. If the coach observes a 10% change in the week on week metrics, they might adjust training or programming based on this information. The noise or the measurement error of the device for that metric, however, could be 12% in which case a training data interpretation error may occur.