they haven't got any freakin titanium in them fer gods sake!!!
read the fall of reach. they get their genes enhanced so their bones are stronger. the MJOLNIR suits make them look like cyborgs, but they are bioengineered humans. this same thread was posted several times about this time last year. MC is john the spartan. get over it
I think you must read them better because if you read it closely you will find that their bones are impregnated with a ceramic sort of stuff just like tank armor.