Jackknife Sit-up
Learn how to do the Jackknife Sit-up with proper form and technique. This body weight exercise primarily targets your Abs, with secondary emphasis on Hip Flexors.
How to Do the Jackknife Sit-up
Follow these steps to perform the Jackknife Sit-up with correct form:
- 1Lie flat on your back with your legs extended and your arms overhead.
- 2Engage your core and lift your legs and upper body simultaneously, reaching your hands towards your toes.
- 3Pause for a moment at the top, then slowly lower your legs and upper body back down to the starting position.
- 4Repeat for the desired number of repetitions.
Jackknife Sit-up Muscles Worked
Primary
Secondary
Exercise Details
- Equipment
- body weight
- Body Part
- waist
- Category
- Extended
Recovery & Training Frequency
- Recommended Recovery Time
- 2–3 days
- Weekly Frequency
- 2–3 sessions per week
- Why
- Medium-sized muscles like the deltoids and traps recover well with 48–72 h between targeted sessions. Higher training frequency (3 ×/week) is viable when volume per session is modest.
Sets & Reps by Goal
Strength
- Sets
- 3–4
- Reps
- 5–8
- Rest
- 90–120 s
Isolation movements can be trained with moderate loads for strength, though peak strength expression is secondary to compound lifts.
Hypertrophy
- Sets
- 3–5
- Reps
- 10–20
- Rest
- 45–90 s
Isolation exercises shine in the 10–20 rep range with a 2-second eccentric. Taking the final set close to failure drives maximum hypertrophic stimulus.
Endurance
- Sets
- 2–4
- Reps
- 20–30
- Rest
- 20–45 s
Light-load, high-rep isolation work is useful for rehab, joint health, and pump-focused training.
Which Workout Splits Include Jackknife Sit-up?
Based on the muscles this exercise targets, it fits naturally into these training splits and day types:
Full Body
Any session
Bro Split
Abs/Core Day
Not sure which split is right for you? Cora builds personalised training plans that match your schedule and goals. Learn more about progressive overload.
Related Exercises
Frequently Asked Questions
What muscles does the Jackknife Sit-up work?
The Jackknife Sit-up primarily targets your Abs. Secondary muscles worked include Hip Flexors. This makes it an effective exercise for developing your waist.
Do I need equipment for the Jackknife Sit-up?
No. The Jackknife Sit-up is a bodyweight exercise that requires no equipment. You can perform it anywhere with enough space.
How do I perform the Jackknife Sit-up with proper form?
Start by Lie flat on your back with your legs extended and your arms overhead. Engage your core and lift your legs and upper body simultaneously, reaching your hands towards your toes. Pause for a moment at the top, then slowly lower your legs and upper body back down to the starting position. Focus on controlled movement throughout the entire range of motion. See the full step-by-step instructions above for complete form guidance.
How often should I do the Jackknife Sit-up?
For most people, allow 2–3 days between sessions targeting the same muscle group. That translates to 2–3 sessions per week. Medium-sized muscles like the deltoids and traps recover well with 48–72 h between targeted sessions. Higher training frequency (3 ×/week) is viable when volume per session is modest.
What are the best sets and reps for the Jackknife Sit-up?
It depends on your goal. For strength: 3–4 sets of 5–8 with 90–120 s rest. For hypertrophy (muscle growth): 3–5 sets of 10–20 with 45–90 s rest. For endurance: 2–4 sets of 20–30 with 20–45 s rest.
Which workout splits is the Jackknife Sit-up best for?
The Jackknife Sit-up fits well into the following training splits: Full Body (Any session), Bro Split (Abs/Core Day). It is classified as a core movement.
Track Jackknife Sit-up in Cora
Cora creates AI-powered workout plans that adapt to your recovery. Log exercises, track progress, and get personalized coaching.
Download Cora for iOS