i didn't read through the whole thread... but i have one word..
EVOLUTION...
humans are constantly adapting to their surroundings and to the chores at hand... so that they can do them better, with less effort etc..... so look at the backgrounds of each specific race/culture, look at their diets, their activity, their agriculture, their games they played for fun, and you will see exactly how they evolved to handle the tasks at hand.. bigger stronger legs for climbing more hills.. bigger upper body for doing more barn work... skinnier/faster running for handling long distance treks between desert villas... etc etc
btw.. noone mentioned samoans.. those are some big bastards.. not really all that strong.. but big nonetheless.. oh yeah... they did a study in hawaii on the samoans... the fat ones.. which is close to the whole population.. anyway, they put them back on a diet of fish, poi, fruits.. and they just shredded the fat off.. americans/japanese made them fat.. when we settled on their land and brought our flour, hamburgers, and steak, etc etc.. we made them fat cause their bodies were not accustomed to the food..