Stability Ball Knee Tuck
Also known as: stability ball jackknife
- Primary muscleAbs
- EquipmentStability Ball
- DifficultyIntermediate
- TypeCore · Core flexion
- Secondary muscles
- Hip Flexors
- Body part
- Core
- Position
- Lying
- Laterality
- Bilateral (both sides together)
- Category
- Strength
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From a plank with your shins on the ball, pulling the knees in rolls the ball toward your hands while the shoulders hold everything level, so the abs flex the trunk and brace it at the same time. The ball drifting sideways tells you which obliques are slacking - feedback a bench tuck never gives.
How to do the Stability Ball Knee Tuck
- Start by sitting on the stability ball with your feet flat on the ground and your knees bent at a 90-degree angle.
- Place your hands on the sides of the stability ball for support.
- Engage your abs and slowly roll your hips forward, bringing your knees towards your chest.
- Pause for a moment at the top of the movement, then slowly extend your legs back to the starting position.
- Repeat for the desired number of repetitions.
Tip: Breathe out as you crunch and let the last bit of air leave the lungs at the top of each rep.
Muscles worked
Primary
Abs · Core
The rectus abdominis shortens to bend the spine forward, and each rep should end with the upper abs fully contracted and the ribs pulled down.
Secondary
- Hip Flexors — The hip flexors take over if your feet are anchored and you come up too high; keep the range short to leave them out.
Common mistakes
- Pulling on the neck — hands behind the head should support, not yank; keep the elbows wide and the chin about a fist away from the chest.
- Sitting all the way up — a crunch is a curl of the ribs toward the pelvis, not a sit-up; the lower back should stay on the floor the whole time.
- Cranking out fast reps — momentum does the work if you bounce; lift to a squeeze, hold for a count and lower slowly.
- Never adding load — once bodyweight reps get easy, hold a plate on the chest or use a cable rather than doing sets of 50.
Where it fits in a workout
Crunches close out a session after the heavy work, or they can fill the rest periods between sets of a lift that does not need much bracing. Pair a cable crunch with a cable side bend on the same stack.
How many sets, how heavy and how hard: see what the ACSM position stands support.
Variations and alternatives
Similar exercises
Without stability ball
When to talk to someone
- Chest discomfort, feeling faint or lightheaded, or trouble breathing during or after exercise can be signs of a heart attack. In the US, call 911 right away; elsewhere, call your local emergency number.
- Heart, metabolic or kidney disease, or symptoms like these when you are active: talk to your doctor before you start or step up training.
- Pregnant: ask your obstetric care provider which exercise suits you.
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More exercises
Sources
- ACSM position stand on exercise quantity and quality (Garber et al., 2011)
- ACSM preparticipation health screening (Riebe et al., 2015)
- ACOG Committee Opinion No. 804 on exercise in pregnancy (2020)
- CDC: About Heart Attack Symptoms, Risk, and Recovery (2024)
Sources checked on October 17, 2026. Full citations are in the exercise library.
Animation and exercise data: ExerciseDB, licensed to SetGrip. General information, not medical or coaching advice.