2.6. External Load

The external variables employed in this study were: accelerations (Acc); decelerations (Dec); distance covered (Dis); steps (St); maximum speed (Vmax); average speed (Vavg); impacts (n), PlayerLoad^TM (Pl) and Metabolic Power (Pmet).

Firstly, the number of accelerations (Acc) and decelerations (Dec) per game and period were determined, as well as Acc and Dec per minute in each period. The value established for its calculation was greater than 1 or −1 m/s².

The variables of distance covered (meters) and steps (n) were measured through the inertial device, taking its values by periods and throughout the game.

The maximum speed (Vmax), the average speed (Vavg), and different speed zones were determined for the speed variable. The ranges of speed zones were: V₁ = 0–6 km/h (walking); V₂ = 6–12 km/h (jogging); V₃ = 12–18 km/h (running); and V₄ = 18–21 km/h (sprinting). These ranges of speed were established according to criteria developed by Gómez-Carmona and Pino-Ortega, [19] and based on the characteristic demands of basketball officiating.

Impacts were measured by G-forces that the referees experienced during different game actions. The calculation of this variable was achieved by summing the vector of G-forces that the referee experienced across three axes (x, y, and z). The impact value was established when the G-forces of the movement exceeded 5 Gs [35].

The variable of PlayerLoad (PL) was defined as the sum of the acceleration vectors as assessed through the inertial device employed (WIMU PRO^TM) and in each of the three axes (vertical, anterior-posterior, and lateral). The PlayerLoad variable has demonstrated strong reliability and validity indices [36,37] to assess the neuromuscular load of each referee [38]. The corresponding value was calculated through the following equation, where Z represents acceleration from the anterior to posterior direction, X refers to acceleration in the medial-lateral direction, and Y refers to vertical acceleration. Time is represented by t and n refers to number.

The variable of Metabolic Power (PMet) was obtained by multiplying the velocity (V) by the energy cost of the activity (EC), as represented by the rate of acceleration [39]. The value was obtained through the following formula: