A ring biceps curl with an enormous stretch under load — the book says it gets the biceps "sore like nothing else." Doubles as elbow-tendon prep for the Front Lever and Muscle-Up (Rings). You already do these.
Cues
Rings set low, lean back with arms extended behind/below you for the stretch, curl your body up. Standardize ring height + foot position so you can progress it consistently. → Progression
⚠️ Ease in — the stretched position is intense on the elbow. Start with less lean.
Programming
3 × 6–10. Not a beginner move; you're past that.
How to progress
More lean / feet further forward = harder leverage. Tempo the eccentric. → Progression §5