I’ve been using an exercise called the Bear Crawl with some of my clients lately. It really seems to challenge them aerobically and strength-wise and forces the core to work quite hard to stabilise the hips while crawling.
Here is a tiny clip from ACE showing you how it’s done.
No equipment needed; no claws, fur or fangs, though a growl could lighten the mood!
Why not crawl around your house or office, when no one is watching!