Emulating a muscle in rapier

[Timothy-Gonzalez]

Hello! I'm looking to emulate a piston / muscle like motion, like the following:

A
|
|
B

To:

A
|
|
|
|
B

And back.

Is there a good way to do this? I tried using motors but only ended up with rotation, not translation.

I also tried arbitrarily setting local anchors but that caused the joints to ignore physics and glitch out.