[jmdocherty]

Probably not what you're looking for but it works for me. If you're physically able, take up running. It doesn't have to be far or fast just getting outside is enough. Listen to an inspiring podcast or audiobook while you do it ("how I built this" is my favourite). As extra motivation to get out, I don't allow myself to listen to that when I'm not running. Running is really time efficient. HIIT is also good for 20-30mins of exercise but it doesn't work for me because I can't listen to a podcast and hear the instructions.

When I'm back at my desk I'm far more productive & energised. I make it a daily habit and leave all the kit in the same place so it's easy to do it on those "off" days.