If you do something manfully, you do it in a brave, determined way, even when it is hard, heavy, or a bit embarrassing. You keep going and you do not make a fuss. The word is rather old-fashioned. It comes from an older idea that “like a man” meant “bravely.” You still see it in stories, and in slightly humorous writing: someone manfully trying not to cry, or manfully finishing a huge plate of food. Younger speakers more often say bravely or with determination. Some readers also feel the word sounds as if only men can be brave, so it carries that old colour whether you like it or not. It is an adverb: it tells you how someone did something. It is not a common school-essay word today, but you will meet it in books.

勇敢地、堅毅地（偏舊）