The small ball, sometimes called a reform ball, Pilates ball, or soft ball, is one of those pieces of equipment that most home practitioners discover later than they should. It looks modest. It costs less than a reformer session. And yet it changes almost every Pilates exercise it touches: more core activation, more inner thigh engagement, more precise hip alignment. Once you add it to your practice, it becomes hard to train without it.
Here is what the reform ball actually does, and how to use it well at home.
What Is a Reform Ball?
A reform ball (also called a small Pilates ball or mini soft ball) is a partially inflated rubber or PVC ball, typically 20cm in diameter. Unlike a stability ball, which is designed to support your full body weight, the reform ball is a prop, held between the knees, placed under the lower back, squeezed between the thighs, or pressed against the wall in standing work.
The key is that it provides gentle, consistent resistance through compression. When you squeeze it, you activate the inner thighs, the deep hip stabilisers, and the pelvic floor simultaneously. That combination is exactly what classical Pilates targets, and it is notoriously difficult to isolate without a prop.
The name "reform ball" comes from its use as an affordable reformer alternative for home practitioners. Many of the inner thigh and hip-stabilising cues used in reformer exercises translate directly to small ball work on the mat.
Why It Works
Three mechanisms make the reform ball effective:
Adductor activation. Squeezing the ball between the knees or inner thighs fires the adductors, muscles most people underuse in standard mat work. Strong adductors stabilise the pelvis, reduce hip hiking, and support knee health during lunges and single-leg exercises.
Pelvic floor feedback. When you squeeze the ball, you get tactile feedback that you are engaging correctly. For postpartum practitioners rebuilding pelvic floor awareness, this is particularly useful, the ball gives you something to work against, making an invisible contraction feel concrete.
Spinal decompression. Placed under the sacrum or lower lumbar in supine exercises, the ball gently elevates the pelvis, creating traction along the lower spine. Articulating through a supine bridge over the ball feels meaningfully different to flat-mat work, more range, more feedback, more release in the lumbar facets.
The Best Reform Ball Exercises for Home Pilates
1. Supine Bridge with Ball Squeeze
Lie on your back, knees bent, feet flat. Place the ball between your knees. Inhale to prepare. Exhale, squeeze the ball and peel your spine off the mat one vertebra at a time, pelvis, lumbar, thoracic, until you are in a straight diagonal from knees to shoulders. Hold for two breaths. Inhale at the top, exhale to articulate back down. Repeat 10–12 times.
The squeeze activates the inner thighs and hamstrings simultaneously, preventing the knees from splaying and keeping the pelvis level. Most people immediately feel more gluteal engagement than in a standard bridge.
2. Dead Bug with Ball Press
Lie on your back, arms extended toward the ceiling, knees tabletop. Place the ball between your palms and knees, so both hands press into the ball from above, and both knees press into it from below. Without releasing this pressure, slowly lower your right arm and left leg toward the mat. Return. Switch sides. Repeat 8–10 times per side.
The ball press forces you to maintain the co-contraction that dead bug is supposed to create, but rarely does for beginners without a prop. It becomes an entirely different exercise.
3. Clam Shell with Ball Between Ankles
Lie on your side, knees stacked, hips stacked. Place the ball between your ankles. Without rolling the pelvis back, lift the top knee toward the ceiling as far as hip rotation allows, not further, then lower. Repeat 15 times per side.
The ankle placement creates a longer lever than a standard clam shell, increasing the load on the hip abductors and external rotators. Excellent for glute medius isolation.
4. Inner Thigh Lift
Lie on your side, top leg bent with foot on the mat in front. Bottom leg is long. Place the ball under the bottom ankle for elevation. Lift the bottom leg toward the top foot, then lower with control. Repeat 12–15 times per side.
The ball lifts the leg slightly so you start mid-range, where the adductors are most active. It also prevents the foot from dragging on the mat, which would reduce control.
5. Supine Leg Press with Ball Under Sacrum
Place the ball under your sacrum, the flat triangular bone at the base of your spine, not the lumbar curve. Find a position where your pelvis feels tilted slightly posteriorly and your lower back is in gentle traction. Extend both legs to 45 degrees. Slowly lower to 60 degrees and return. Repeat 10 times.
This is a strong lower abdominal exercise. The ball elevates the pelvis, increasing the demand on the lower rectus abdominis and hip flexors while decompressing the lumbar spine. It is also genuinely useful for menstrual cramp relief, the sacral elevation can reduce referred tension.
6. Standing Wall Squat with Ball
Stand with your back against a wall, feet hip-width apart, roughly 30cm from the baseboard. Place the ball between your knees or inner thighs. Slide down the wall until your thighs are at 45 degrees, not a full squat, which shifts emphasis to the quads. Hold for 30 seconds, squeeze the ball lightly throughout. Return to standing. Repeat 3–4 times.
This is the closest home equivalent to the reformer's standing leg press. Adductors, glute medius, and vastus medialis all fire isometrically. Your knees will feel this the next day.
How to Inflate It Correctly
Reform balls should be partially inflated, firm enough to hold their shape, soft enough to compress 2–3cm when squeezed firmly. Fully inflated, they become too rigid to create useful feedback. Underinflated, they offer no resistance.
A good test: press your palm firmly into the ball. It should give noticeably but spring back. If it collapses flat, add air. If it does not give at all, release a little.
The RIVI Reform Ball (20cm) comes with a pump and valve, the same system used in the RIVI Stability Ball. It inflates in under two minutes and deflates for flat storage.
Adding It to Your Existing Practice
If you already practice with a mat kit, the reform ball slotted into your existing sequence in 6–8 exercises without restructuring anything. Start by adding it to bridges and dead bugs, the two exercises where the feedback is most immediately obvious, and build from there.
If you are working from a kit that includes resistance bands, the ball and bands complement each other well: bands for posterior chain, upper back, and hip abduction; ball for anterior core, inner thigh, and hip stabilisation. The combination covers a full mat session without any equipment overlap.
You can browse the full RIVI individual equipment range or see which kits include reform balls in the Pilates collection.
Who It Is Best For
The reform ball is genuinely useful across experience levels, but it earns its place fastest for:
- Practitioners who feel their inner thighs are undertrained in standard mat work
- Postpartum returners rebuilding pelvic floor and core co-contraction
- Anyone with lower back sensitivity who finds flat-back supine work uncomfortable
- People moving from studio reformer to home mat who want to preserve some of the reformer-specific load
It is less essential for practitioners whose primary interest is upper body, balance, or flexibility, the stability ball and resistance bands serve those goals better.
Further reading:
- The best stability ball exercises for a stronger core at home
- The best Pilates ring exercises for your home practice
- How to set up a home Pilates gym you will actually use
- I did Pilates every day for 30 days at home
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