The system is called miCoach, and it uses two main pieces of hardware. There's a "data cell," basically a collection of sensors, that fits into a small pocket in the player's "base layer" (read: fancy sports undershirt), sitting between the shoulder blades. But there are also some sensors woven right into the fabric of the base layer--this connected fabric is actually what senses heart rate and other vitals. The data cell itself is incredibly light, at only 52 grams, though it's not as small as I expected. It's got the usual array of sensors: a tri-axis accelerometer, GPS, magnetometer, gyroscope. Every player in all 19 teams ("clubs," says the press release, because Europe) will wear it.