Another good approach: done is often better than perfect. 

It may help because I usually use walking after I’m done with something - as a way to reward myself. I have yet to use walking as a method for my mind to marinate ideas, but it seems to be the to-go method for some Stackers. I will experiment with it sometime.

What worked just now was a hangry 18-month-old demanding for her breakfast! You betcha I didn’t ruminate on my slides. Finished them in record-breaking time n settled her physiological need. If those participants find my slides lacking, too bad. Haha

cryotosensei

Design

Is inertia inevitable?

This probably won't be much help, but I usually dive into a project after it starts occupying my attention. 

Maybe you could manufacture that situation by going for a walk and thinking about your presentation. Then when you sit down to work on it your mind will already be in high gear.