Strength increasing ability.

Marvel has quite a few that can do this without any outside help such as..
1. Hulk. The madder hulk gets the stronger hulk gets.
2. Thor. Warrior madness?
3. Gladiator. The more confident he is the stronger he gets.
5. Goliath/Atlas. The bigger he gets, the stronger he gets.
Does DC have some that can do this at will? Name them.

Oh yes. Animal Man.

Giganta

Vixen

Swamp Thing

No outside help at all, only pure biology?

-Superman - gets stronger based on emotions.
-Martian Manhunter - can use his own shapeshifting to make himself stronger iirc.
-Vixen/Animal Man can take on aspects of animals that increase their strength and durability
-Geo-Force can use his powers to amp his strength and durability, though I don't recall if DC still requires him to be in contact with the Earth to do so.

Nobody else comes to mind atm.

Edit: DS beat me to some of them.

Plastic Man

Congorilla

Clayface

Atom Smasher.

Damage

Every Green Lantern.

Beast Boy

The Presence

😏

OMAC
Parasite

Jack Hawksmoor

Flex Mentallo

Originally posted by -Pr-
No outside help at all, only pure biology?

-Superman - gets stronger based on emotions.
-Martian Manhunter - can use his own shapeshifting to make himself stronger iirc.
-Vixen/Animal Man can take on aspects of animals that increase their strength and durability
-Geo-Force can use his powers to amp his strength and durability, though I don't recall if DC still requires him to be in contact with the Earth to do so.

Nobody else comes to mind atm.

Edit: DS beat me to some of them.

Too many to name. They're not as dynamic as the Hulks ability but there are some that can do the amping thing.

Animal Man can go from a bacterium to a Sun Eater. That's way more dynamic than Hulk