Impossible for writers with an appreciation of all the Middle encompasses to write a sagging Middle.
I've written extensively in previous blogs about the Middle being:
- Territory of the Antagonists
- The Exotic World
(2 Tips for bolstering the Middle)
To add to that, the scenes in the Middle are made up of opportunities for the protagonist to learn the skills and knowledge she needs in order reign victorious at the Climax and achieve her long-term goal.
Though she is unconscious or oblivious of her need to learn new skills and knowledge, you as the writer are fully conscious. Put her in scenes that challenge her weaknesses and show her what she needs to learn by allowing the antagonists to interfere with her efforts and movement toward her goal.