The idea of a squiggle from the leg of an octopus is what makes it so tough. I discuss with locals the tradition of whacking fresh octopus on a rock. But frankly this folklore is not what it seems and in order to tenderize octopus you need know-how and not the shear brut force of a divers arm.
Hyper redundant manipulators they are called by scientists who study their brut force as an example of how mother nature works. They have a very large number of actuatable degrees of freedom that intrigues scientists when it comes to robotics.
But what we care about is eating it, and so how do we manage the proteins in octopus to get it tender. They begin to dissolve at 54C and you need to manage the time when cooking it. I often cook it at 77C for 4-5 hours and its tender.
But if you haven’t the time, try to wash it to remove the blockers, those very pores that protect the octopus and keep it water functional. They key is to activate and cleanse the body and prepare it for 7 minutes of cooking depending on its size.