The plank!
A plank done in proper form will work your core stabilizers better than almost anything. This grouping of muscles is critical body conditioning for almost everything we do as we age not to mention the health of our back.
https://www.healthline.com/health/fitness/what-muscles-do-planks-work
Have a great week!
Danielle Pointon
Live Blue Consulting
I am back training on water- plank kept me fit all winter plus a few more things:-)