Which tractate of the Talmud describes physical ideals for men?

I was reading some of the Daf Yomi columns in Tablet magazine and saw that the write-up of “chapter 9 of Tractate Nedarim” mentions that “the rabbis had a physical ideal for Torah scholars: They were supposed to be frail, emaciated by study.”

I’ve been looking at the authors old columns and can’t find this cited in any specific columns—except maybe as an interpretation of the story of Rabbi Yehuda being accused of looking like a pig farmer. Any ideas where this frail, emancipated ideal of a Torah scholar is from?