How to hold an animation while pressed?

How do you get a character to throw a punch or whatever type of animation and have it stay in that position as long as I hold the button down? For example, I reach out and grab or punch something, and then as long as I hold the button down, the hand stays extended, reached out and only goes back to idle one I release the button.

A quick way I can think of is to create a Blend Space of the animation at idle and the animation of the hand extended. Set idle to 0 and extended to 1 (or whatever values you want) and when you click the mouse you should set a variable to equal 1 that will set the animation to the extended animation and when you release, set that variable back to back to 0