I don't know if I'd recommend using one. I can clean 200lbs and from my chest push it over my head. I by no means could this to a 150lbs guy. I could shoulder him or body lock and lift etc etc. My point is that these submissions are not difficult in and of themselves, they are difficult because some ass hole is resisting. Controlling a moving, defending opponent is the hard part. And IMO is the vastly important thing.
The greatest use I could see for such a doll would simply be practicing your movements, transitions and maybe explosive submissions you couldn't try rolling cause it's dangerous.
I'd say 6 months of practice with this doll and instructionals would be equivalent with 2 weeks of bjj in a real gym.
If a law is unjust, a man is not only right to disobey it, he is obligated to do so. ~ Thomas Jefferson
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