Which muscles does the jackknife sit up work?

The jackknife sit up mainly works your abs. It also involves your hip flexors.

How many sets and reps should I do?

A common starting point is 2 to 4 sets of 8 to 12 controlled reps, with a weight that leaves a couple of reps in reserve. Adjust it to your goal and experience, and stop if something hurts.

How do I track the jackknife sit up in SweatByte?

Add it to a routine or a workout. Log the reps for each set. SweatByte shows your last session's numbers on every set, so you know what to beat.

Jackknife Sit Up: how to do it and muscles worked

The jackknife sit up mainly works your abs, with help from your hip flexors. You need bodyweight (no equipment).

Muscles worked

Main

Helping

Hip flexors

How to do the jackknife sit up

1
Lie on your back with your arms stretched overhead and your legs straight, ready to fold.
2
Sit up and bring your knees to your chest at the same time, folding your body together like a jackknife.
3
Lower back with control, then extend your arms and legs again without letting them touch the floor between reps. Breathe out as you fold.

Form tip: Do not use momentum; if you cannot do it smoothly, bend your knees more or shorten the range.

Common questions

Which muscles does the jackknife sit up work?: The jackknife sit up mainly works your abs. It also involves your hip flexors.
What equipment do I need for the jackknife sit up?: You need bodyweight (no equipment).
How many sets and reps should I do?: A common starting point is 2 to 4 sets of 8 to 12 controlled reps, with a weight that leaves a couple of reps in reserve. Adjust it to your goal and experience, and stop if something hurts.
How do I track the jackknife sit up in SweatByte?: Add it to a routine or a workout. Log the reps for each set. SweatByte shows your last session's numbers on every set, so you know what to beat.

More abs exercises

General information, not medical advice. Learn the movement with light weight first, and see a doctor or physiotherapist if you have an injury or pain. More guides in Learn.