What is the change in (directional) ground speed going one way and going the other way, with constant airspeed?
In still air?
In a headwind?
It's the change which matters, and it's the same in both cases.
50 knots IAS and a 50 knot headwind = 0 knot GS.
Turn 180 degrees, maintaining 50 KIAS - you're doing 100 knots GS. Change of 100 knots.
50 KIAS in still air and you're doing 50 knots GS.
Turn 180 degrees, maintaining 50 KIAS - you're still doing 50 knots GS, but going the other way. Absolute change of 100 knots.