TETSUBack Extension On Exercise Ball vs Sphinx
The Back Extension On Exercise Ball and the Sphinx both train the spine as their primary muscle. The Back Extension On Exercise Ball uses a stability ball while the Sphinx is bodyweight-only. Here is how they compare and when to pick each.
Side-by-side comparison
| Back Extension On Exercise Ball | Sphinx | |
|---|---|---|
| Primary muscle | spine | spine |
| Body part | back | back |
| Supporting muscles | glutes and hamstrings | glutes and hamstrings |
| Equipment | stability ball | bodyweight |
| Steps in our guide | 5 | 5 |
How each one starts
Back Extension On Exercise Ball — first steps
- Place the stability ball on the ground and lie face down on top of it, with your hips resting on the ball and your feet against a wall or other stable surface.
- Position your hands behind your head or crossed over your chest.
Sphinx — first steps
- Lie face down on the ground with your forearms flat on the floor, elbows directly under your shoulders.
- Engage your core and lift your chest off the ground, keeping your forearms and toes on the floor.
Full step-by-step guides are linked below.
Which should you choose?
The Back Extension On Exercise Ball adds an unstable surface that raises core demand. The Sphinx needs no equipment and scales through leverage, tempo and reps. If your gym has both options, neither is a wrong choice: pick the one that feels strongest through a full range, and swap after 6 to 8 weeks to keep the spine adapting.
Full form guides
Common questions
Is the Back Extension On Exercise Ball better than the Sphinx?
Neither is universally better — both train the spine as the primary mover. The Back Extension On Exercise Ball adds an unstable surface that raises core demand, while the Sphinx needs no equipment and scales through leverage, tempo and reps. Choose based on your equipment and which movement you can progress consistently.
Can I do both the Back Extension On Exercise Ball and the Sphinx in the same program?
Yes, but usually not in the same session — they overlap heavily on the spine. A common setup is one as your main movement and the other on a second training day, or alternating them block by block.
Do the Back Extension On Exercise Ball and the Sphinx work the same muscles?
Yes — the primary muscle is the same (spine) and both rely on the same supporting muscles: glutes and hamstrings.
Track it in Tetsu
Tetsu tracks both movements separately, keeps your PRs per exercise, and tells you which one is actually progressing. Free to start.