I've made up a blog post about good work out you can do to improve your riding position and strength with Meryl Wheeler, the creator of Pop Fitness. She holds a fitness program for equestrian.
Check it out, there are a lot of great things you can do.
A fitness trainer answered to our questions during a ask session a few weeks ago, her name is Holly Ward, here is a link of one of her answers:
There are a lot of interesting answers 🙂