Wearable-based tracking technologies are used throughout sport to support performance monitoring. But how do they work, what do they measure, and how do they benefit athletes and coaches?
At the most fundamental level, a wearable tracking device calculates position by timing the signals emitted by GPS satellites orbiting the Earth.
Each satellite continually transmits messages that include the time of transmission and the satellite’s position at that time, information that the receiver uses to compute the distance to each satellite using the speed of light. These distances and satellite locations are used to compute the location of the receiver at a specific point in time using a process known as trilateration.
As objects (or athletes) change position over time, their movement profiles (and thus displacement/distance covered) can be plotted by regular repetition of this process. The objects (or athletes) speed is determined using the doppler shift. This is a change in frequency of a wave, in relation to an observer, moving relative to the wave source.
This is the basis by which wearable technology enables us to analyse player movements during training and matches.
Although velocity and positional information is useful in terms of basic speed and distance calculations, Catapult’s wearable tracking devices also contain a number of inertial sensors that enable practitioners to conduct more detailed levels of athlete monitoring.
These inertial sensors comprise an accelerometer (to measure acceleration forces), a gyroscope (to measure rotation), and a magnetometer (to measure body orientation). Inertial sensors collect data in three axes, or directions, allowing sensitive ‘maps’ of athlete movements and actions to be created.
Accelerometers are particularly useful for identifying many athletic movements (e.g. jump or tackle) and understanding large accelerations that may result in small movements.
Catapult devices use tri-axial accelerometers (up/down, forwards/backward and left/right) to measure acceleration at 1000 Hz and record at 100Hz (100 times per second).
Gyroscopes measure rotation around three axes (the coronal plane, the frontal plane and the sagittal plane). The combination of gyroscope and accelerometer data allows us to create more precise pictures of dynamic athlete movements than would be possible with one sensor alone. By combining data in this way, wearable tracking units are now able to facilitate far more detailed analysis of an athlete’s movement.
Catapult units contain tri-axial gyroscopes (the three axes being yaw, pitch and roll) that collect data at 1000 Hz. Measuring speed of rotational movement is particularly useful during sport-specific actions such as a cricket bowling delivery or a baseball pitch.
In essence, magnetometers are an electronic compass that help to understand orientation in relation to magnetic north. In terms of athlete monitoring, magnetometers provide information regarding direction and orientation, helping practitioners to understand the volume of key movements such as changes of direction.
In Catapult devices there are magnetometers in three axes measuring at 100 Hz to add an extra layer to our performance data.
The combination of the wearable tracking device and the inertial sensors creates a powerful athlete monitoring tool that ensures that key performance decisions are always supported with objective data.
These key performance decisions can include performance readiness, rehabilitation, and training prescription.