is there anything wrong with doing them in hard floor?
my nephew who is 12 years old has been doing boxing for about 3 years and about 4 months ago he started doing knuckle push ups he now performs 65 non stop knuckle push ups on either on brick or concrete he does it with a horizontal fist not verticle, now his knuckles dont look "pretty" anymore but his knuckles have gone numb he doesnt feel a thing on his knuckles even if he burns it he doesnt feel it or if he get a needle and tries piercing through it. i wanted to ask people like scrap is this a good thing? or should he stop