I never use thumbs on the hand that's gripping your own wrist.. Depending on his defense, the angle of his resistance pressure, and other factors, i may take the thumb off on the wrist control hand. For the same reason Bmac is saying, throttling that wrist further. Always use the thumb on the wrist control hand in the beginning. Must. I use the kimura alot. There's more to the kimura than the sub, there's sweeps, back takes, armbars, etc.. I use the kimura grip for a back take very often.. Having the thumb on the wrist control hand is a must if you wanna use the kimura grip for positional changes..
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