I've seen many male soccer players - specially famous players who play for well-known teams - wear a piece of clothing that looks like a sports bra. They're usually worn during practice, and a few other times I've seen them worn under the jersey during the games. I'm guessing it has some training benefits, but what is the bra looking thing? What's the purpose of wearing it?
Here are 2 pictures of Lionel Messi and Zlatan Ibrahimovic wearing the bra.
They are performance trackers. They track a player's vital statistics (heart rate, etc) as well as their movement, their average speed, their distance covered, etc. As for the "bra-like" design, it would appear to just be the result of needing a small and unencumbered design that allows for minimal interruption, maximum body contact, and full range of motion.
GB11's answer summarized it well what are the tracking devices. From the YouTube page of GPSSports Systems you can see that what Zlatan wears is called GPSports SPI HPU tracking device, which according to its brochure has many features, some of them being GPS, accelerometer, wireless communication, water resistance, 5.5 hours battery life, etc.
The data collected by tracking device from players is auto-analysed to provide practical information on players' performance, like:
- Establish the session load for each player
- Identify outliers in the group
- Identify players under significant training stress
- Compare sessions to recent history
- Produce high quality reports
- Periodise training using a range of variables
- Monitor individual training demands
- Monitor rehabilitation and reconditioning programs
- Compare players, sessions, drills and games
Note that those kind of tracking devices are used on a very high level in many team sports, and not just in football.
The "bras" contain a small pouch in the back which is used to hold a small GPS device. This device records many different variables such as average speed, distance traveled, fastest recorded sprint, and areas of the pitch that said player has traveled to. The bras are perhaps the most popular method to hold this device but vests and sleeveless shirts are also popular options amongst players who do not enjoy the tight fit of a sports bra.
