The human body ranges from ectomorph through mesomorph to endomorph.
http://www.google.co.uk/search?q=ect...iw=874&bih=659
The ectomorphs are skinny distance runner types, however hard they train they are unlikely to produce discernible muscle bulk, instead of large muscle fibres they produce wiry tough muscles needed to cover distance.
The Cubans choose young ectomorphs as boxers, after intensive training they develop muscle and win heavyweight Olympic gold.
The mesomorphs become sprinters, when trained they develop the big muscles and firm abs. Although they can run distance they prefer not to and tend to spend the winter indoors doing gym and weight training.
The endomorphs end up throwing the shot and discus. They put on a lot of either muscle bulk or fat very easily. They have tremendous power for a short period of time, over 60m they are unstoppable, over 100m they are struggling, they rarely run 200m.
When fit they have dramatic abs.
If you get in a fight with an endomorph learn to dance, block and duck, wait until they tire then wear them down with sharp blows from all directions. You may have longer reach than them so use it.
If you are an ectomorph unless you are willing to perform the Cuban Olympic boxing teams training regime and diet you will never get abs, but some people find that slim is hot.