ST BOOSTS increase the speed at which a player gains STRENGTH PROGRESS and levels up through training and matches.

Boosts increase the rate at which a player develops ST through training and matches. Boosts are available in three tiers: BASIC (silver), PRO (gold) and ELITE (black)

To use a boost:
1) Navigate to your squad
2) Select a player
3) Tap the [+] sign in the ACTION column
4) Drag the boost onto the player

Note that each boost will only apply for a limited time. The better the boost the longer it will last.