An oblique crunch with a ball is a curl up that turns a little to one side. Lying on your back with your knees bent, you hold a small ball in both hands, lift your head and shoulders and reach the ball toward one knee, then lower and reach toward the other knee on the next one. The turn works the muscles at the sides of your trunk (obliques), and the lift itself comes mostly from the six-pack muscle (rectus abdominis). With both hands on the ball, there is nothing to pull on your neck with.

How to do the oblique crunch with a ball

Lie on your back on a mat with your knees bent and your feet flat, a little apart. Hold a small, light ball in both hands just above your chest.
Gently flatten your lower back toward the mat and tuck your chin in slightly, so a small gap stays under it.
Breathe out as you lift your head and shoulder blades from the mat and reach the ball toward one knee, letting your chest turn slightly that way.
Hold the lift briefly. Then breathe in and roll back down slowly, chin still tucked, until your head rests on the mat.
Lift again, this time reaching toward the other knee, and keep alternating sides.

What you should feel

Effort along the side of your waist that does the turning, with the front of your stomach helping. Your neck may work a little but should not ache.

Common mistakes

Throwing the ball forward with your arms instead of lifting with your stomach.
Poking your chin out toward the ball.
Letting your knees drift apart or sway as you turn.
Holding your breath at the top of the lift.

How often

Many programs start with 1 to 3 sets of 8 to 12 reaches to each side at an unhurried pace, 2 or 3 days a week. Your physio will adjust this.

Stop and check with your physio if

Your neck aches more with each lift, or you feel tingling, numbness or pain in an arm.
Pins and needles in your arm or hand that do not go away after you stop, or part of your arm or hand goes numb. Get medical advice the same day. If one side of your face or body suddenly goes numb or weak, or your speech becomes slurred or muddled, call emergency services, even if it goes away.
Back pain that turns sharp, or tingling, numbness or pain traveling down a leg.
Doming or a ridge appears down the middle of your tummy, or a scar from an operation hurts. Stop, and check with your physio before the next session.

From the clinic

The video is filmed at an angle, so the turn is hard to see, but the voice guide asks you to reach toward one knee and then the other. Keep the turn small and let it come from your ribs, not from your arms pushing the ball across. When the voice guide says to lift your back off the floor, it means your upper back and shoulder blades. Your lower back stays on the mat. If you have high blood pressure, breathe steadily through every repetition and never hold your breath.

For a straight lift with no turn, see the curl up. The twisting crunch uses a similar turning lift with the hands at the head instead of on a ball.

Bending the spine forward and turning it at the same time is the combination that osteoporosis exercise advice most often limits. If you have osteoporosis or low bone density, or have had a fracture in your spine, leave this one out unless your physio has cleared it. Ask your physio first, too, if you have been told you have a disc problem, or your back pain spreads into a leg.

A hernia or recent stomach surgery is a reason to get the go-ahead from your physio or doctor first. If you have had surgery on your spine, chest or heart in recent months, get the go-ahead from your surgical team or physio first.

If you have recently given birth, including by cesarean section, or you have a gap down the middle of your stomach muscles (diastasis recti), ask your physio, midwife or doctor first. In pregnancy, leave this one out unless your physio or midwife says it is fine. If you are pregnant and past the first three months, check with your physio before exercising flat on your back. Stop and talk to your physio if you leak urine or feel pressure low in your pelvis as you lift.

Written and checked by the PocketPhysio editorial team. Last updated 2026-09-28.

This page is general education, not a diagnosis or a personal treatment plan. If you have pain, an injury or a health condition, see a physiotherapist or doctor before starting new exercises.

Oblique crunch with a ball