Bending the elbow
Atom, a short guy punching above his weight, is an action hero, as is the Cheyenne Kid; Adam Strange is action (and romance) at the other side of the galaxy, courtesy of a zeta beam; Captain Savage is action at sea and so it goes. Action comics have also featured prominently in Central and South America.

Superman started out in a series called Action Comics and seventy-five years later is still there.

Those figurines bearing the likenesses and attributes of the comic character they're molded on are not dolls, toys, or even replicas - they're action figures. And they remain so even if you paint over them.

Maybe it would be easier to define a comic that wasn't predominantly action-oriented, like Little Audrey.

II

For those used to walking into their local video store and poring over the large Action section, this may seem puzzling. Westerns and Martial Arts and War all have their sections. Perhaps we recognise Action by its generic title convention, its wooden acting, its threadbare plot. It is harder to gauge these things when we move to a more static medium, which carries titles like War Is Hell. The tip-off that characters are not being fully nuanced is only evidenced when, for example, the crop of hacks that Tom de Falco brought to Marvel showed every character with teeth gritted.
And underdeveloped stories are those where the fight scene goes on a tad long and we barely see the main character interacting on other levels.

III

"He swung a punch but missed completely" so the oldest comics tell us. And there's Captain Dependable doing just as the caption says.
But there is a sense that the early writers were feeling their way in a new medium. Novels - especially airport novels and spy thrillers - contain action aplenty but look at this passage from one of the very earliest novels (Joseph Andrews by Henry Fielding, 1742):

Adams had soon put on all his clothes but his breeches, which, in his hurry, he forgot; however, they were pretty well supplied by the length of his other garments; and now, the house-door being opened, the captain, the poet, the player, and three servants came in. The captain told the host that two fellows, who were in his house, had run away with a young woman, and desired to know in which room she lay. The host, who presently believed the story, directed them, and instantly the captain and the poet, jostling one another, ran up. The poet, who was the nimblest, entering the chamber first, searched the bed, and every other part, but to no purpose; the bird was flown, as the impatient reader, who might otherwise have been in pain for her, was before advertised. They then enquired where the men lay, and were approaching the chamber, when Joseph roared out, in a loud voice, that he would shoot the first man who offered to attack the door. The captain enquired what fire-arms they had; to which the host answered, he believed they had none; nay, he was almost convinced of it, for he had heard one ask the other in the evening what they should have done if they had been overtaken, when they had no arms; to which the other answered, they would have defended themselves with their sticks as long as they were able, and God would assist a just cause. This satisfied the captain, but not the poet, who prudently retreated downstairs, saying, it was his business to record great actions, and not to do them. [...]