For whatever reason, Mega Man's as spritely when he's one hit from violently exploding as he is when at full health, and there's actually an explanation for it besides "video game." Mega Man's a robot, so he would probably not have any stamina, meaning he couldn't get exhausted, even if he suffers massive damage. It is possible that Mega Man in his "civilian form" for lack of a better word would have "simulated stamina" for the purposes of making him more human, but those get disabled while in "Combat form" as being able to get exhausted would be a handicap then.