A movement snack is two minutes of moving placed between two tasks. That is the whole idea.
Stand up. Walk to the far window and back. Do a few slow stretches. Climb a flight of stairs. Pick one and keep it short.
The trigger is the gap you already have: the end of a call, a finished email, the wait for a file to load.
Two minutes is small enough that you will not talk yourself out of it. That is the point of keeping it small.
Three or four of these across a working day add up without ever feeling like a workout or needing a plan.
No equipment, no clothes to change, no schedule to keep. Move, sit back down, carry on.
If movement causes pain rather than the usual stiffness, ease off and check with a qualified healthcare professional.