As pre-season preparations continue for Premier League clubs, it has become commonplace to see players wearing vests over their tops on the training field.
But why? What do they do?
“The vests have a GPS unit in the back,” explains Crystal Palace’s assistant performance analyst Mike Eglon.
“That will track the distance they run, the speeds that they’re running, their accelerations and decelerations."
As Eglon continues in the video below the vests also have built-in "intensity indicators", meaning that players have no place to hide.
Have you ever wondered why the players wear those black vests in training? 🤔
— Crystal Palace F.C. (@CPFC) July 8, 2017
Wonder no more! 💪😅 pic.twitter.com/2PDp8EyzSn
Palace's pre-season continues when they take part in the Premier League Asia Trophy, in Hong Kong, on 19 and 22 July.