Full time manual focus on USM lenses

Hello,

I know that USM lenses allow Full time manula focus, so that you can turning the focusing ring in one shot after focus achieved while keeping pressed halway the shutter button.

The question is: if if turn the focus ring WHILE the lens is autofocusing, so while the lens is moving, can I damage the lens?

For example the lens is going from macro mode toward infinite and I turn the ring in the opposite direction, can I damage the lens?

Some say no, because there are no gears with USM lenses... Canon doesn't tell anything about...

Thanks a lot!!!

Marco