Extensions
Core extensions train the muscles of the lower back — primarily the erector spinae and multifidus — through spinal extension. They are the direct counterpart to crunch variations and the most overlooked movement pattern in core training.
Most people who do any direct core work at all do some version of a crunch. Far fewer include extension work, which creates an imbalance between the front and back of the core that shows up as lower back weakness, poor posture under load, and discomfort during compound movements like deadlifts and squats. The lower back is half of the core equation and deserves the same direct attention as the front.
The back extension is the foundational movement here — the torso hinges at the hip, lowering toward the floor and extending back to neutral or slightly beyond. Done well it trains the erector spinae through a meaningful range of motion and builds the kind of lower back resilience that carries over into every compound movement you do. The dead bug, while less obviously an extension movement, trains the lower back isometrically while the limbs move — a more subtle but highly functional variation.
These movements don’t need to be heavy or dramatic to be effective. Bodyweight back extensions done consistently build meaningful lower back strength. Load can be added progressively once the movement is solid.
Below are the extension variations in the library.
Reference Card
Movement Pattern: Spinal extension Primary Muscles: Erector spinae, multifidus Secondary Muscles: Glutes, hamstrings
Variations
- Back extension
- Weighted back extension
- Hyperextension machine
- Dead bug
Considerations
- The lower back is half of the core — neglecting extension work creates an imbalance that affects posture and compound lift performance
- Bodyweight is an appropriate starting point — add load only once the movement pattern is solid
- The dead bug trains the lower back isometrically while challenging coordination — it’s more demanding than it looks
- Extension work supports lower back health across all compound movements
Programming Notes
- Works well at the end of a session alongside other direct core work
- Responds well to moderate rep ranges (10–15) with controlled tempo
- Including extension work consistently is one of the more practical things you can do for long term lower back health