Trigger Rush

Trigger Rush is one of the companion perks in Fallout 4.

Obtaining
To gain the perk, the Sole Survivor must be at maximum affinity with Cait, which is possible after completing her personal quest (Benign Intervention).

Effects
The official description in game is: The player character's Action Points regenerate +25% faster, if the Hit Points value is below 25% of its maximum.

However, this perk has never functioned this way. When the player's Action Points are below 25 points, they regenerate 50% faster which makes this perk a good way to recover those first few action points much faster if you regularly run out of action points (regardless of how much health you have).