According to the Theory of Evolution:
‘Evolution is the change in the inherited characteristics of biological populations over successive generations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.’
So, according to the Theory, it will take many generations of successive breeding is order for your offspring to reach a level of your satisfaction. Not to mention that your kids might chose not to become fitness enthusiasts and workout junkies after all.