## 2 Materials and Methods
### Equipment  
Eight WIMU PROTM inertial devices (RealTrack Systems, Almeria, Spain) were used in this research (Figure 1). Each device had its own internal microprocessor, 2 GB flash memory and a high-speed USB interface, to record, store and upload data. The devices were powered by an internal battery with 4 h of life, had a total weight of 70 g and dimensions of 81 \(\times\) 45 \(\times\) 16 mm. The devices were composed of different sensors (four accelerometers, a gyroscope, a magnetometer and a GNSS and UWB chipset, among others [24]). S PROTM software (RealTrack System, Almeria, Spain) was used to analyze and export the data of the x- and y-position coordinates.  
This UWB system was designed to alleviate any satellite reference problems by using time-based positioning techniques, in which the signal propagates from the transmitter (antenna) to the receiver (device). The transmitter in an UWB system is a set of antennas (4, 6, 8 or more) that transmit the radiofrequency signal almost under the same principle as the GPS system [24], except in this case, this reference system is fixed and is not affected by environmental conditions [25]. The ultra-wide band system occupies a very large frequency band, at least 0.5 GHz, as opposed to more traditional radio communications which operate in much smaller frequency bands. On the other hand, since UWB is only allowed to transmit at very low power, its spectrum becomes very noise-like and it can coexist with other services without influencing them.  
Thus, if all nodes (transmitters and receivers) have a common clock, the receiving node can determine the time of arrival (TOA) of the incoming signal and directly calculate its distance from the transmitter, thus multiplying the estimated TOA by the speed of light allows the drawing of a circle with the reference node at its center and a radius equal to the estimated range. By collecting at least three measurements (trilateration 2D) and intersecting the defined circles, it is possible to determine the position of the receiver node/target (Figure 2). If the target receives UWB signals from more than three references, in normal conditions, the accuracy of the position measurement increases [26].  
Figure 1: (**Left**): Device used in the present study; (**Right**): Participant wearing the device.  
The UWB system is composed of two sub-systems: (i) The reference system and (ii) the devices tracked (carried by the participants). The reference system is composed of antennas that are transmitters and receivers of the radio frequency signal (see Figure 3). The antennas (mainly the master antenna) perform the computerizing of the position of the devices that are in their area of performance, while the devices receive that calculation.  
Figure 3: (**a**) Antenna distribution of the UWB system and distance reference to the basketball court. Red lines indicate distance from the antennas to the court and grey lines indicate communication between antennas. (**b**) Reference system process: (i) Four devices were placed in the corners of the basketball court and registered position data during 1\({}^{\cdot}\). (ii) Centroid data of the set of points obtained were calculated as the corner reference of the perimeter of the court. (iii) Finally, the routes designed with real measures (measured with a trundle wheel) were introduced in the generated template.  
Figure 2: Trilateration process to determine the device position (Reference = antenna; d = distance; TARGET = participant).