maratoolJackknife Sit-Up
How to do the 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
The prime movers are the rectus abdominis and the obliques, which flex the trunk forward and resist it being pulled into extension or twisted out of line.
Every exercise for:Abdominals
How this movement works
The load travels toward you and several joints bend to bring it there. The arms finish work the back starts, so grip and elbow flexors sit in the path of every repetition: when people stall on a compound pull, it is more often the hands giving out than the primary muscle running out of force.
It is filed under strength: produce force against resistance for a countable number of repetitions, and progress the resistance over time.
What you need
No equipment at all. The resistance is your own bodyweight, so you progress by changing leverage, range or tempo rather than by adding plates — and you can do it anywhere.
Every exercise using:Body only
These train the abdominals too, using equipment this one does not:
- Kettlebell Figure 8kettlebell
- Kneeling Cable Crunch With Alternating Oblique Twistscable
- Landmine 180'sbarbell
- Medicine Ball Full Twistmedicine ball
- Side Bend with Dumbbelldumbbell
Difficulty
Listed at beginner level: the pattern is simple enough to pick up without coaching, and a position that goes wrong mid-set is obvious enough to correct on the next repetition.
Of the 97 abdominals exercises in this database, 69 are listed at beginner level.
Photos: free-exercise-db — public domain (Unlicense) Full attribution →
ⓘ Informational only — not a substitute for professional fitness or medical advice.