Skip to content
Crucible Fit
  • The Crucible
  • The Week
  • Programs
  • Train Your Way
  • Pricing
Get Crucible
  • The Crucible
  • The Week
  • Programs
  • Train Your Way
  • Apple Watch
  • Pricing
  • FAQ
  • Training Guides
Get Crucible
Crucible Fit

A daily functional fitness test for iPhone, Apple Watch and Android. Stations, reps and the Crux, sized to your readiness and your kit.

Download on the App StoreGet it on Google Play

Crucible Fit

  • The Crucible
  • The Week
  • Programs
  • Train Your Way
  • Apple Watch
  • Pricing

Explore

  • Training Guides
  • Exercise Library
  • FAQ
  • Press
  • Support

Legal

  • Terms and Conditions
  • Privacy Policy
  • Consumer Health Data Notice

CRUCIBLE FIT™ and Crux by Crucible Fit are trademarks of Crucible Fit, LLC.

© 2026 Crucible Fit, LLC. All rights reserved. Apple, the Apple logo, iPhone and Apple Watch are trademarks of Apple Inc., registered in the U.S. and other countries. App Store is a service mark of Apple Inc. Google Play and the Google Play logo are trademarks of Google LLC.

  1. Home
  2. /
  3. Exercises
  4. /
  5. Chest
  6. /
  7. Seated Under Knee Clap On A Chair

Exercise guide

Seated Under Knee Clap On A Chair

  • Intermediate
  • Compound
  • Rep-based
  • Chest
  • Shoulders
  • Upper arms
  • Waist

This beginner-friendly core exercise targets the lower abdominals and obliques while improving hip flexor mobility and coordination. The seated position provides stability, making it an effective way to isolate the midsection through a controlled crunching motion.

Reviewed by the Crucible Fit team · Updated June 2026

Watch the Seated Under Knee Clap On A Chair demonstrationVideo and instructions for every movement are in the Crucible Fit app.

Muscles worked

Primary

  • Abs
  • Obliques

Secondary

  • Biceps
  • Deltoids
  • Lats
  • Triceps

Equipment

  • Body weight

Setup

  1. Sit upright on the edge of a sturdy chair or flat bench with your feet flat on the floor, hip-width apart.
  2. Engage your core by pulling your navel toward your spine and maintain a tall posture with your chest lifted.
  3. Extend your arms out to your sides at shoulder height or keep them ready to move toward your midline.

How to do it

  1. Exhale as you lift your right knee toward your chest while slightly leaning your upper torso forward to meet it.
  2. Bring both hands together under your raised thigh and perform a quick clap.
  3. Inhale as you lower your leg back to the floor and return your torso to the upright starting position.
  4. Repeat the movement immediately with the left leg, alternating sides in a rhythmic, controlled tempo.

Form checklist

  • Keep your back straight and avoid excessive rounding of the spine during the clap.
  • Lift the knee high enough so that you don't have to hunch over excessively to reach underneath.
  • Maintain a tight core throughout the entire set to protect your lower back.
  • Ensure your movements are deliberate and avoid using momentum to swing your legs.

Pro tips

  • Focus on the 'mind-muscle connection' by imagining your ribs pulling down toward your pelvis as you lift the knee.
  • Pause for a fraction of a second at the moment of the clap to maximize the peak contraction of the abdominals.

Make it harder

  • Perform the exercise without letting your feet touch the ground between repetitions, keeping your legs hovering to maintain constant tension.
  • Hold a small light weight or weighted ball in your hands while performing the under-leg pass instead of a clap.

Frequently asked

What muscles does the seated under knee clap on a chair work?
The seated under knee clap on a chair primarily targets the abs and obliques, and also works the biceps, deltoids, lats, and triceps as secondary muscles.
What equipment do you need for the seated under knee clap on a chair?
The seated under knee clap on a chair requires no equipment — just your body weight.
Is the seated under knee clap on a chair good for beginners?
The seated under knee clap on a chair is rated intermediate. Build a base with simpler variations first, then progress to it with light load and strict form.

Related exercises

  • Barbell RolloutAdvanced · abs, lats, and obliques
  • Bear WalkIntermediate · abs, calves, deltoids, hamstrings, obliques, and pectorals
  • Behind The Head Ball SlamIntermediate · abs, calves, lats, obliques, and pectorals
  • Body Saw PlankIntermediate · abs, lats, 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.

Download on the App StoreGet it on Google Play

See how a Crucible works