Flexible/J.E. Sawyer's Fallout RPG
Years of exercise have made you incredibly supple. You can change stance in half the time of a normal person - it costs you 50% less action points.
J.E. Sawyer's Fallout Role-Playing Game
You can change from prone to stand and still participate in other phases of combat. Also, you can change from prone to crouch or crouch to stand as a free action at the beginning or end of your movement phase.