Sublime Force does let you amplify your own strength. Actually, the material reinforcement was invented because early practitioners kept breaking their own weapons by swinging them too hard.
The 'not on biological stuff' wasn't meant to mean you can't use it to reinforce your own power, it was meant to mean 'no, you can't tap the guy and make his skeleton explode out from his other side'. Might have been more clear if I'd said foreign biological stuff... Though picking up a branch and using it to parry a sword is still ok so that's still not utterly accurate.
Basically I guess the best way to put it is that you can't use it on the other guy directly, you need something to carry that force, but that something can definitely be your own fist if you've the need.
Anyway, most users prefer to do it with tools anyway, because 'I swung too hard and broke my sword' is less critical then 'I swung too hard and broke my hand and upper arm'. Using intermediaries to transfer the force means that, usually speaking, if you mess up on the self reinforcement the intermediary breaks, not your bones. And no one likes accidentally breaking their own bones. It kinda hurts, you know?
