There are a number of approaches to measuring a player’s activity, also known as their external load. In GPS systems such as Catapult One, this loading is typically measured as distance covered or the high-speed distance covered or even the energy expended.
Another approach involves the calculation of Player Load based on the inertial sensor data collected in a session.
The Player Load metric uses the accelerometer data to calculate the load or activity level of the player. Research has shown that Player Load is a valid and reliable measure and can provide important insights into player activity.
Player Load is the sum of the accelerations across all axes of the internal tri-axial accelerometer during movement. It takes into account the instantaneous rate of change of acceleration and divides it by a scaling factor (divided by 100).
The scaling factor is used to reduce the total value of the Accumulated Player Load, thereby making it easier to work with during analysis.
This parameter tells you how much work the player did during a training session or game. It is a volume measure. The number itself is an arbitrary unit, meaning it is to be used as a scaling factor to compare the total volume of work performed.
For example, a player that has a Total Player Load of 300 did 50% more work than a player that has a Total Player Load of 200. This number is best used to evaluate how much work a specific player has done over time, or to compare how much work that player did in a specific training session compared to previous sessions.
What is the Player Load formula?
Player Load is calculated in the Catapult One system using the established algorithm as explained in a number of academic publications (see below).
In the case of the Catapult One system the accelerometer operates at 400hz which is smoothed to 100hz with the Player Load calculated as follows:
where axi, ayi and azi are the acceleration values in x,y and z directions respectively,
and i = 0, …, n represents the sampled accelerometer points with n+1 points over the time of the session.
Instantaneous Player Load Formula
fwd: forward acceleration
side: sideways acceleration
up: upwards acceleration
You can access the Player Load data in the Sessions or Squads page as one of the standard volume metrics provided.
It is important to understand that the Player Load values are not directly comparable between players as they are dominated by the impacts that result from locomotive (or running) activity and these values are very much dependent on the running style of players. Values for players who cover similar distances in a ninety-minute soccer game can often range from 400 to 800 or even higher.
For this reason, when comparing Player Load values between players for training or even games, it is better to use the Player Load for the session in question as a percentage of the player’s typical game Player Load value. This can be shown by clicking on the % option at the top right-hand corner of the Squads chart. Of course, the Player Load value for a game for a player must be set first.
When examining this data look for major differences in loading values between players to indicate sessions that may have been significantly harder on certain players than others. It is also important to look at the loading values over time to understand if the periodised training plan is matched by the loading levels.
Player Load vs Distance Parameter
It has advantages over using distance as an effort metric because it accumulates during tackles, ruck work, or other non-running activities. However, for an athlete whose main activity is running, there will be a strong correlation between distance covered and Player Load. This is because the heel strike force generates vertical accelerations (for example) which feed into the Player Load formula (see figure below).
Who created the Player Load variable?
This Player Load formula was originally developed at the Australian Institute of Sport (AIS) as a proposed metric for measuring effort in a rugby union application.
Supporting Academic Publications
 A comparison of methods to quantify the in-season training load of professional soccer players. Scott BR1, Lockie RG, Knight TJ, Clark AC, Janse de Jonge XA. Int J Sports Physiol Perform. 2013.
 Accelerometer and GPS-derived running loads and injury risk in elite Australian footballers. Colby MJ1, Dawson B, Heasman J, Rogalski B, Gabbett TJ. J Strength Cond Res. 2014
 Accelerometer derived load according to playing position in competitive youth soccer. Barron D, Atkins S, Edmundson C, Fewtrell D. International Journal of Performance Analysis in Sport, 2014.