I do for one full hour non-stop of 2,000 sit ups and then 6 sets of leg rise.
Genetics help to some degree, but the most important thing is the mind and the spirit. These two are even more powerful than physical characteristics that are passed on.
My MIND POWER gave me this body.
To be tired it is only in your mind.
If you don't like don't do it. But don't forget that: NO PAIN NO GAIN.
I love to be sore and when I feel sore I train even harder.