Jackknife Sit-Up
A beginner compound strength exercise that works the abs, needing no equipment.
Starting position
End position
How to Do Jackknife Sit-Up
- Lie flat on the floor (or exercise mat) on your back with your arms extended straight back behind your head and your legs extended also. This will be your starting position.
- As you exhale, bend at the waist while simultaneously raising your legs and arms to meet in a jackknife position. Tip: The legs should be extended and lifted at approximately a 35-45 degree angle from the floor and the arms should be extended and parallel to your legs. The upper torso should be off the floor.
- While inhaling, lower your arms and legs back to the starting position.
- Repeat for the recommended amount of repetitions.
Muscles Worked
Alternatives to Jackknife Sit-Up
10 movements that train the same primary muscle, closest substitutes first — same kind of training, then variations of the movement itself, then a similar difficulty.
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1
Janda Sit-Up
A beginner isolation strength exercise that works the abs, needing no equipment.
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2
Sit-Up
A beginner isolation strength exercise that works the abs, needing no equipment.
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3
Press Sit-Up
An advanced compound strength exercise that works the abs, using a barbell.
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4
Weighted Sit-Ups - With Bands
An intermediate isolation strength exercise that works the abs.
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5
Barbell Side Bend
A beginner isolation strength exercise that works the abs, using a barbell.
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6
Bosu Ball Cable Crunch With Side Bends
A beginner isolation strength exercise that works the abs, using a cable machine.
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7
Cable Crunch
A beginner isolation strength exercise that works the abs, using a cable machine.
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8
Cable Judo Flip
A beginner compound strength exercise that works the abs, using a cable machine.
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9
Cable Reverse Crunch
A beginner isolation strength exercise that works the abs, using a cable machine.
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10
Cable Russian Twists
A beginner compound strength exercise that works the abs, using a cable machine.
Frequently Asked Questions
What muscles do jackknife sit-up work?
Jackknife Sit-Up primarily works the abs.
What equipment do I need for jackknife sit-up?
None. Jackknife Sit-Up is a bodyweight movement you can do anywhere you have floor space.
Jackknife Sit-Up: is it suitable for beginners?
Yes. Jackknife Sit-Up is rated beginner. Movements you can learn in a session, with a low skill floor and a forgiving failure mode.
What can I do instead of jackknife sit-up?
Janda Sit-Up, Sit-Up, Press Sit-Up train the same primary muscles and are listed with 7 more alternatives above.
Can Fitnit count my jackknife sit-up reps automatically?
Not automatically yet. Fitnit's AI rep counting covers push-ups, squats, dumbbell curls, crunches and pull-ups today; jackknife sit-up can be logged manually in the app, and tracked movements are added over time.
Photographs and step-by-step instructions from free-exercise-db, a public-domain exercise dataset. Muscle mapping and alternatives by Fitnit.
Track Your Jackknife Sit-Up with AI
Fitnit automatically tracks push-ups, crunches, squats, pull-ups, and curls with advanced body tracking technology — and you can manually input any other workout too. Start free — Pro is $8.99/month.