It's difficult not to get bruised at first, enthusiasm and even a little of the dreaded macho syndrome creep in. Apart from the obvious, avoid bruisng, eventually you'll know what level of pounding will cause it and won't be shy to speak up.
Hits to the head are problematic and I really don't want to start conditioning mine - I use it for other things (honestly). I guess having conditioned arms helps cover up or block and when doing so we can totally forget about our iron clad torsoe

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It's surprising how little force is needed to break a rib which is left to "stand alone". I think that whist this can be improved by "closing" it's still a weak area.
In the midway of this our mortal life ...