Questions on Old Threads

I’ve been going through a lot of the old threads on the forum over the past few days and I learned a lot. However, I’m not completely sure about some things so I thought I’d post my questions here. If anyone would like to help me out with any of them it would be appreciated.

General vs Specific:
1.Elite sprinters engage in primarily general lifts because their somatotype is already in place, but would more specific training be better for people trying to build a particular somatotype?
2.I’ve avoided deadlifts because there was no eccentric portion and developing mainly concentric strength wouldn’t optimally increase the eccentric and isometric strength through the p-chain, which was most important in sprinting. Does the general vs. specific idea mean that I should do deadlifts even though they take up a lot of CNS resources and don’t do that much for overall ecc and iso strength?

Long Duration Isos:
3.How do you progress on these? Do you just keep going for longer and longer times or do you add weight at some point?

Stiffness:
4.What exactly is stiff when stiffness is exhibited at max speed? Previously I thought having stiff tendons and muscles was necessary, but is it actually that the muscles must be stiff and the tendons must be very flexible and have a lot of give in order to get a good bounce off of the track?