The RRG says that a Hero's activation is over when the hero uses their second action and has no movement points remaining, but that he doesn't have to use all of either. The RRG also says that a hero can take a strain to gain a movement point up to twice per activation if the hero has enough endurance to cover it. My question is, if a Hero uses his second action and has no movement points left can the hero take strain to gain movement points and then use those before the activation ends?

Yes, using strain for MP is not an action. So you could use two Strain, move two spaces, then attack twice.

I know you can take strain to get additional MP. I feel like I was pretty clear about that in my original post. My question is a specific timing question. Can you take strain to gain MP, after you've used both of your actions and have no MP remaining? The RRG states that your activation is over at that point, but it doesn't say you can or can't take the strain for additional MP first.

You can spend strain after your second action, before your activation is over, even if you have no movement points left. Essentially, you are interrupting yourself to give yourself movement points.

"Activation", RRG, Page 3:

Abilities that trigger “during” a figure’s activation are used before or after either of that figure’s two actions.

Basically it ends when you say so...

Basically it ends when you say so...

I have been using that excuse with my son for a few years now.