The following examples, which have been extracted from different journal articles, illustrate the inconsistencies in the meanings that have been assigned to PL: However, some aspects of PL definition and equation do not seem to be clear moreover, in the recent past, problems related to its physical quantity (i.e., the use of arbitrary units) have also been noticed by other researchers ( Staunton et al., 2017).Ĭonsequently, we observed possible difficulties in understanding the meanings that are attached to PL as a descriptor of the external load. Since the introduction of this equation in the sports sciences literature, PL has been widely used across different sports contexts ( McNamara et al., 2015 Schelling and Torres-Ronda, 2016 Wilk et al., 2017 Young et al., 2016). The aforementioned definition, which is presented in Montgomery et al.’s (2010) and Boyd et al.’s (2011) works, is accompanied by the following PL equation: To the best of our knowledge, PL was first defined in sports sciences literature as “a modified vector magnitude, expressed as the square root of the sum of the squared rates of change in acceleration between each moment of a training session in each movement axis (x, y, and z)” and it is represented in arbitrary units ( Boyd et al., 2011 Montgomery et al., 2010). PL can be calculated based on the acceleration data that are recorded by triaxial accelerometers. A commonly used variable to describe the external load is Player Load (PL), which is a term that has been proposed by Catapult Sports, a company that provides sports technology. Studies on sports training have used inertial sensors to measure the external load, which is the physical demand that is experienced by players during training or competition ( Castillo et al., 2017) (e.g., distance covered, mean velocity, and accelerations Schelling and Torres-Ronda, 2016 Weaving et al., 2017).

We concluded that a deeper discussion of Player Load as a descriptor of external load is warranted in the sports sciences literature. Therefore, coaches and sports scientists should take this information into account when they use Player Load to prescribe and monitor external loads. It seems that Player Load is related to the magnitude of changes in acceleration, but not the magnitude of acceleration itself. Moreover, the use of arbitrary units and different practical meanings in the literature has associated Player Load with many physical quantities, thereby resulting in difficulties in determining what Player Load measures within the context of sports. Accordingly, this paper presents a brief discussion on the meanings that have been assigned to Player Load, its limitations, and the lack of clear and complete information about Player Load calculation methods. We reviewed existing literature in order to understand Player Load better we found many inconsistencies in PL calculation methods and in the meanings attached to it. Our motivation to write this paper came from the difficulties that we encountered in the calculation and interpretation of Player Load using our own data, since we did not use the Catapult Sports equipment, which is a merchandise of the company that proposed this variable. We present a critical reflection on the mechanical variable Player Load, which is based on acceleration data and commonly used in sports.

Catapult definition