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  1. Home
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  3. Exercises
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  5. Core & Abs
  6. /
  7. Lying Knee Raise

Exercise guide

Lying Knee Raise

  • Beginner
  • Compound
  • Rep-based
  • Waist

The Lying Knee Raise is a foundational core exercise that primarily targets the lower abdominals and hip flexors by using the weight of the legs as resistance while the lower back remains supported.

Reviewed by the Crucible Fit team · Updated June 2026

Watch the Lying Knee Raise demonstrationVideo and instructions for every movement are in the Crucible Fit app.

Muscles worked

Primary

  • Abs
  • Obliques

Secondary

  • Erector spinae

Equipment

  • Body weight

Setup

  1. Lie flat on your back on a comfortable mat with your legs extended.
  2. Place your arms straight by your sides with palms down, or tuck your hands slightly under your glutes for extra lower back support.
  3. Engage your core by pressing your lower back firmly into the floor to eliminate any arching.

How to do it

  1. Exhale as you bend your knees and pull them toward your chest in a smooth, controlled motion.
  2. Continue the movement until your thighs are past vertical and your hips slightly lift off the floor to maximize abdominal contraction.
  3. Inhale as you slowly lower your feet back toward the starting position using a 2-second eccentric tempo.
  4. Stop just before your feet touch the ground to maintain constant tension on the abdominals before starting the next rep.

Form checklist

  • Keep your lower back glued to the floor throughout the entire range of motion.
  • Avoid using momentum or swinging your legs to lift your knees.
  • Keep your neck neutral and shoulders relaxed; do not strain your head upward.
  • Focus on the 'crunch' of the pelvis toward the ribs rather than just moving the legs.

Pro tips

  • Initiate the movement by performing a posterior pelvic tilt, tucking your tailbone toward your chin before the knees even move.
  • Squeeze your knees and ankles together to create full-body tension and better stabilize the pelvis.

Make it harder

  • Straighten your legs into a Lying Leg Raise to increase the lever arm and resistance.
  • Add a 'hip pop' at the top of the movement, driving your feet toward the ceiling to further engage the lower abs.

Frequently asked

What muscles does the lying knee raise work?
The lying knee raise primarily targets the abs and obliques, and also works the erector spinae as secondary muscles.
What equipment do you need for the lying knee raise?
The lying knee raise requires no equipment — just your body weight.
Is the lying knee raise good for beginners?
Yes. The lying knee raise is a beginner-friendly movement and a strong foundation to build on.

Related exercises

  • 3/4 Sit-UpBeginner · abs and obliques
  • 45 Degree Bicycle Twisting CrunchIntermediate · abs and obliques
  • 45 Degree Lean Back Alternate Knee RaiseBeginner · abs and obliques
  • 45 Degrees Arms PlankIntermediate · abs, deltoids, obliques, and pectorals

Train it with Crucible Fit.

Every movement in this library is in the app with video and instructions, ready for your own sessions on the days between Crucibles. Your first Crucible is on us.

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