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  1. Home
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  3. Exercises
  4. /
  5. Core & Abs
  6. /
  7. Sitting Knee Tuck On A Chair

Exercise guide

Sitting Knee Tuck On A Chair

  • Beginner
  • Compound
  • Rep-based
  • Lower legs
  • Upper legs
  • Waist

This beginner core exercise targets the lower abdominals and obliques by utilizing a seated position to isolate the midsection while moving the lower body. It is highly effective for building foundational core strength and hip flexor stability without requiring floor space.

Reviewed by the Crucible Fit team · Updated June 2026

Watch the Sitting Knee Tuck On A Chair demonstrationVideo and instructions for every movement are in the Crucible Fit app.

Muscles worked

Primary

  • Abs
  • Obliques

Secondary

  • Hip flexors
  • Quadriceps

Equipment

  • Body weight

Setup

  1. Sit on the front edge of a stable chair with your feet flat on the floor and knees bent.
  2. Grip the sides of the chair seat firmly with both hands to stabilize your torso.
  3. Lean back slightly (about 20-30 degrees) while keeping your spine neutral and chest open.

How to do it

  1. Exhale and engage your core to pull both knees toward your chest in a controlled motion.
  2. Inhale as you slowly lower your feet back toward the floor, stopping just before they touch the ground.
  3. Maintain a steady tempo of two seconds for the tuck and two seconds for the extension.

Form checklist

  • Keep your chest lifted and avoid rounding your lower back as you tuck your knees.
  • Ensure your shoulders remain down and away from your ears throughout the movement.
  • Maintain a slight bend in the elbows to avoid locking out your arms while gripping the chair.
  • Keep your knees and ankles squeezed together to maintain tension in the lower abdominals.

Pro tips

  • At the peak of the tuck, pause for one second and focus on pulling your belly button toward your spine for maximum contraction.
  • To better engage the obliques, slightly rotate your knees toward one shoulder at the top of the movement, alternating sides each rep.

Make it harder

  • Straighten your legs completely during the extension phase to increase the lever length and resistance on the abs.
  • Hold a light object, such as a water bottle or small pillow, between your feet to add weighted resistance.

Frequently asked

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

Related exercises

  • 45 Degrees Arms PlankIntermediate · abs, deltoids, obliques, and pectorals
  • 90 To 90Beginner · abs, glutes, obliques, and quadriceps
  • 90 To 90 SwitchIntermediate · abs, glutes, obliques, and quadriceps
  • Air BikeIntermediate · abs and obliques

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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