Knees off Floor Stability Ball Back Extension
In SetGrip: Stability Ball Back Extension (Knees off Floor)
- Primary muscleSpine
- EquipmentStability Ball
- DifficultyIntermediate
- TypeCompound · Hip-dominant
- Secondary muscles
- Glutes, Hamstrings
- Body part
- Back
- Position
- Prone
- Laterality
- Bilateral (both sides together)
- Category
- Strength
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Straightening your legs and floating the knees leaves only your feet on the wall and hips on the ball, so the glutes and hamstrings must hold tension for the entire set, not just at the top. That constant posterior chain demand is what separates it from ball extensions done with knees grounded.
How to do the Knees off Floor Stability Ball Back Extension
- 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 for stability.
- Position your hands behind your head or crossed over your chest.
- Engage your core and slowly lift your upper body off the ball, extending your back until your body forms a straight line from your head to your heels.
- Pause for a moment at the top, then slowly lower your upper body back down to the starting position.
- Repeat for the desired number of repetitions.
Tip: Keep the neck neutral and look at the floor a few feet ahead of you, not up at the ceiling.
Muscles worked
Primary
Spine · Back
The spinal erectors work both to hold the back in a rigid position and to bring the torso up, and you should feel a burn along both sides of the lower back.
Secondary
- Glutes — The glutes drive the hip extension that lifts the torso, and rounding the upper back slightly with a pelvic tuck shifts more of the work onto them.
- Hamstrings — The hamstrings assist hip extension and get more of a stretch the straighter your legs are on the pad.
Common mistakes
- Hyperextending at the top — the goal is a straight line from head to heels, not an arch; stop when the torso is level with the legs.
- Pad set too high — if the pad sits above the hip crease it blocks the hips from folding and forces the lower back to do all the bending; set it just below the hip bones.
- Using momentum — swinging the torso up fast turns it into a bounce; take two or three seconds on the way down and lift smoothly.
- Adding weight too early — bodyweight sets of 15 with a full pause at the top should feel easy before you hold a plate.
Sets, reps and where it fits
| Goal | Sets × reps | Rest |
|---|---|---|
| Strength | 4–5 × 3–6 | 2–3 min |
| Muscle growth | 3–4 × 6–12 | 90–120 s |
| Endurance | 2–3 × 12–20 | 60 s |
Back extensions are a good accessory after deadlifts or squats, or a stand-alone lower back builder on an upper body day. They pair well with a hamstring curl or a reverse hyperextension on adjacent equipment.
Variations and alternatives
Similar exercises
Without stability ball
Frequently asked questions
What muscles does the Knees off Floor Stability Ball Back Extension work?
The Knees off Floor Stability Ball Back Extension primarily works the spine. It also involves the glutes and hamstrings, which assist the movement and stabilise the joints.
Is the Knees off Floor Stability Ball Back Extension good for beginners?
It is rated intermediate, so it suits people who already train regularly. Beginners can still do the Knees off Floor Stability Ball Back Extension with light load and a spotter or coach watching the first few sessions; if it feels awkward, pick an easier variation from the alternatives below first.
What can I do instead of the Knees off Floor Stability Ball Back Extension?
If you cannot do the Knees off Floor Stability Ball Back Extension, try the Prone Back Extension, the Back Extension or the Flat Bench Hyperextension. Each of them trains the spine through a similar movement, so you can swap them in without changing the rest of the workout.
How many sets and reps should I do?
It depends on your goal. For the Knees off Floor Stability Ball Back Extension, a sensible starting point is strength: 4–5 × 3–6 with 2–3 min rest; muscle growth: 3–4 × 6–12 with 90–120 s rest; endurance: 2–3 × 12–20 with 60 s rest. Put it early in the session while you are fresh, before isolation work for the same muscles.
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