These are the Underarmour Alter Ego Baselayer tops licensed from Marvel and DC.
Apparently “UA Compression gives your muscles that extra boost they need when you’re working hard. But you know what else it does? It makes you feel damn near invincible. It turns you into exactly what you want to be, every time you workout or compete. This is Under Armour® Alter Ego: the baselayer built for heroic performance.”
So basically, you put one on and you instantly get muscles like this guy.
And not at all like these guys.
Kudos to the all-around Iron Man suit design though… and thanks to Little Bleeder Greymouser for pointing it out.