Why our players train with black half vests on

RichGo

Star Player
Sports science and stats, it seems

http://www.skysports.com/football/news/11095/10502787/statsports-the-training-technology-used-by-arsenal-man-city-barcelona-and-more?

Every heartbeat, footstep and breath is recorded and analysed.... and every inch they run, jog or walk is tracked by a GPS.
 

;