My striking regime consists of strikes with all parts of the hands:
- The metacarpal surface below the pinky finger,
- The first two knuckles from the thumb downwards,
- The forefinger in isolation,
- All three middle fingers at once,
- The back of my hand much like a back-handed slap and,
- An open palm with the focus on the centre of the palm at the point Nei Lao Gong.
In order to strengthen all parts of the hand and (this is the part you are obviously not receiving) signal bone re-modelling throughout the whole hand.
My fingers are fine, albeit calloused on the internal surface but my fingertip sensitivity has not changed.
My range of motion in all aspects of hand movement is totally unchanged and this is because I am appropriately applying the liniment and performing hand exercises and stretches in between times, lack of which would indicate poor technique and form.
As for your analogy about 'squishy' hands (referring to hands which have not been hardened which makes the discussion almost irrelevant but anyway) here are some stories which may seem like science fiction to you:
https://www.brisbanetimes.com.au/nation ... wpei8.html
http://www.dailymail.co.uk/news/article ... onths.html
http://www.dailymail.co.uk/news/article ... rison.html
http://www.mirror.co.uk/news/shocking-v ... ch-5654147
https://www.ncbi.nlm.nih.gov/pubmed/12664983
The human skeleton is designed to remodel itself to the applications and stresses it encounters. Since human bone is made not only from calcium but magnesium, manganese, phosphorous and other heavy metal deposits, it can become quite hard when the cellular make-up of said bone is signaled to increase the deposition of its composite elements.
Further to this, diseases of the bone occur when the bone degradation exceeds the bone remodeling, leading to porous bone diseases like osteoporosis, a condition in which bones can break from very minor trauma such as a light knock or fall.
As for breaking bricks... I'll leave this one to you to figure out.
Go and get a large bone from a cow or a sheep and whack a couple of good quality bricks with it.
The problem with your argument is that you are talking about a person who has not trained their hands whatsoever.
It's obvious you have limited life experience and have been around or witnessed some terrible things, such as fights where people get their skulls cracked open and bystanders have to rush in and hold their heads together until help arrives.
I have seen these things in person, and the people causing the damage were not iron palm practitioners, they were just assholes.
Naturally, much of my reply to you is in the same tone as you have shown because I don't believe you are actually asking Shael how he is going out of natural curiosity but because you seem intent on trying to prove a point which is based on your own limited and narrow view of the world.