He does sit-ups every day and now has a noticeable four-pack.

four-pack 是由 four（四）和 pack（一组、一包）组成的复合词。在健身语境中，pack 常用来指腹肌的分块，four-pack 特指"四块腹肌"，这是比常见的六块腹肌（six-pack）少两块的状态。