Here's another way of looking at it: I recently saw this image from the play "The Butler Didn't," currently being shown at the Metropolis Performing Arts Center in Chicago. You might remember a statement I made a while back in this blog: nothing is more visually interesting than a beautiful woman. While I still hold to this idea, the actors compensated for this. Both women are in the foreground and are dressed very nicely.
So, why is your attention first brought to the young man in the dull grey suit behind them? Well, for one, he's in mid-air. It also helps that he's in the center of the composition. But there's still two beautiful women--one wearing a short, bright red dress--that are closer to the viewer, and therefore much larger compositionally. Let's look at this through the magic of silhouette-vision (i.e. 20 minutes of work in Photoshop).
Notice how subtle the two women's poses are. The one on the right is holding a wine bottle in front of her, which protrudes it from her silhouette, drawing attention to it, but no one in this composition is crazier than the guy in mid air. His arms and legs are protruding in all different directions. The larger man in the way back has no way of drawing attention to himself other than the fact that he is wearing the brightest color on the stage. If he wanted to draw attention to himself, the best thing he could do would be to take whatever it is he's holding onto and hold it above his head. That would reveal it from his silhouette and spread out his body more.
Creating a unique silhouette is essential in communicating an idea. In the case of action, the storyteller's job is to convince the audience that an action is occurring. Though subtlety is just as important as extremes, it should be quite obvious that the more extreme a pose is, the more clear it is what is happening. With all of this in mind, look at every one of Captain America's poses from these two pages by Jack Kirby. There are probably about a thousand reasons why Kirby's work is great, but these two pages are especially good at demonstrating how a good, unique silhouette does wonders for an action sequence.
Shameless plug: that's my brother, Michael Woods, doing the crazy jump. He's an actor in Chicago; if you're ever in the area, go see a play.