Question about the source of Super strength and durability.

Where exactly does the strength come from, like say superman, no matter how strong he gets, he never gets bigger, so is the strength really in his muscles or what. Do most superheros have like, super condensed muscles like Stitch (lilo and stitch) or are they getting this strength from another source that is somehow making their muscles stronger, same for the durability.

Can superheros turn their durability on and off, like say superman, luke cage, drax the destroyer, or thor to allow themselves to be hurt?

Superman has his strength and durability due to two main factors.

1. Kryptonian genetics
2. His cells have absorbed plenty of solar energy

Thor is half Asgardian and half Elder God, his strength can be explained due to his heritage as well.

Keep in mind that larger muscles do not equal into increased strength.

Both Superman and Thor are muscular.

Seeing as to how their natural durability is a result of their heritage/genetics, no they cannot just turn it off.

@vptwarrior: Honestly it depends on the character where their strength and durability comes from. As was previously stated Thor and Superman are like that due to their alien physiology. Characters like Spider-man however have condensed muscles and enhanced bone structures allowing them to take punishment.

As I said though this is utterly dependent on the charater themselves so you may need to ask a more spercific question if you are looking for an answer on a single character in particular.

Yep, another thing that adds to it is if they have accelerated healing, that means that they don't build up fatigue toxins as fast as a normal person so they can perform at peak strength longer.