Its quite tricky to be a rly good runner you have to know when and what to relax and hold joints

arms are usefull for keeping balance but u can choose not to move them (but just like mocu said they do have a weight)

Chest will certenly screw you'r run it would make u fall on side and you will have no choice but to do a jump or something like that

in my opinion if ur weight is too heavy and its not possible to regain you'r balance then I suggest you do a roll,its rly easy you just have to contract both of ur knees and make yourself look like a ball and then poof extend them but dont fully do that after you kick the ground
arms are important in rolling too, if you need more information on how to roll then just ask ;)