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Floor Jack-Knife

Strengthen your core with the Floor Jack-Knife! A challenging bodyweight exercise to sculpt your abs and improve stability.

The Floor Jack-Knife is a compound exercise that mainly works the core, with help from the lower back. No equipment needed: it uses just your bodyweight.

Floor Jack-Knife demo video 2
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Floor Jack-Knife Muscles Worked

Primary

Abdominals (rectus abdominis)

Secondary

Hip Flexor (iliopsoas); Spinal Erectors (erector spinae)

How to do the Floor Jack-Knife

Exercise Classification: This core strengthening exercise, known as Jack Knife Floor, targets primarily the abdominals while also engaging the hip flexors and lower back. This exercise can be performed without any equipment and is primarily done using body weight.

  1. Start by sitting on the floor with your legs extended in front of you and your hands placed on the floor behind you for support.

  2. Lean back slightly, engaging your abdominals to help maintain balance.

  3. Bend your knees and pull them toward your chest while contracting your abdominal muscles.

  4. Keep your back straight and avoid using your hands to pull your legs up; the movement should originate from your core muscles.

  5. Straighten your legs out again, returning to the starting position without letting your feet touch the floor.

  6. Repeat the movement for the desired number of repetitions and sets, maintaining control throughout the entire range of motion.

  7. Ensure you breathe consistently throughout the exercise, exhaling as you contract your abdominals and inhale as you extend your legs.

Note: It is important to perform the exercise with proper form to avoid strain on your back or neck. If the exercise feels too challenging, consider modifying the movement by keeping your knees bent throughout the movement or performing a different type of core exercise that aligns with your fitness level.

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Floor Jack-Knife FAQs

What muscles does the Floor Jack-Knife work?

The Floor Jack-Knife mainly works the core, with help from the lower back. The main muscles are the rectus abdominis.

What equipment do you need for the Floor Jack-Knife?

None. The Floor Jack-Knife is a bodyweight exercise, so you can do it anywhere.

Is the Floor Jack-Knife a compound exercise?

Yes. It's a compound movement, meaning it trains several muscle groups at once rather than isolating one.

What are some Floor Jack-Knife variations and alternatives?

Similar exercises include the Band Jackknife Sit-Up, Crunch, Half Jackknife and Hollow Rock.

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