How to do the Jackknives
Primary: Core · also works Obliques, Hip Flexors, Lower Back.
Jackknives are a challenging abdominal exercise that also engage the obliques, hip flexors, and lower back. They are performed by lying on your back and simultaneously raising your upper body and legs to form a 'V' shape, similar to a folding jackknife. This exercise helps enhance core strength, stability, and coordination, providing an effective way to work the entire core region.
Step by step
- 1
Start by lying flat on your back with your arms extended straight above your head and your legs fully extended.
- 2
In one smooth motion, lift both your legs and your upper body towards each other, reaching your hands towards your feet.
- 3
Pause for a moment when your hands and feet meet, ensuring a strong contraction in the abs.
- 4
Slowly lower back to the starting position with control.
- 5
Repeat for the desired number of repetitions.
Coaching cues
- Engage your core muscles throughout the entire movement to maintain balance and control.
- Avoid using momentum; perform the exercise slowly and with control to maximize muscle engagement.
- Keep your legs as straight as possible, only bending slightly if necessary for comfort.
Sets, reps and where it fits
Muscle
3–4 × 10–15
rest 60–90 s
Strength
not a strength lift
use for assistance
Fat loss
3 × 10–15
rest 45–60 s
Jackknives alternatives
Same movement pattern, different equipment or difficulty. Swap one-for-one in any plan.
Frequently asked questions
What muscles does the Jackknives work?
Primary: Core. Secondary: Core, Obliques, Hip Flexors, Lower Back
How many sets and reps of Jackknives should I do?
For muscle: 3–4 sets of 10–15 reps. For strength on compound lifts: 4–5 sets of 4–6. Rest 60–120 seconds between sets.
What can I do instead of the Jackknives?
Same movement pattern, different equipment: Bicycle Crunch, Bird Dog, Crunch, Dead Bug, Flutter Kick, Lying Leg Raise.
Is the Jackknives good for beginners?
With some training experience, yes. Beginners should start with one of the easier alternatives listed and progress to it.