they make a last/cushioning for an average size person .they are in-effect designed for a size 9- 5'10"-65kg person.
when i buy a pair of size 13's and stick em on my 6'4" 90kg body - add to that a 15kg pack and they cant cope.
they should of course beef it up when the weight and shoe size increases otherwise they fall apart, the flex point becomes more in a bigger size, the cushioning gets squished out. the soles wear down quicker.
its quite simple really and i should have known better. of course inno8 should also, am i being mis sold ? or am i just stupid.?