Seated Knee Tuck

Beginner Isolation 30% of bodyweight

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A seated core exercise balanced on your buttocks, pulling the knees toward the chest from a lean-back with straight legs. Trains the abs, with the obliques and hip flexors helping to hold the balance.

Also known as: Crunch Frog, Frog Crunch, Seated In and Out, Seated Tuck Crunch

How to do the Seated Knee Tuck

  1. Balance on your buttocks, legs straight, arms out to the sides.
  2. Pull your knees toward your chest, reaching your arms forward.
  3. Extend your legs and open your arms without touching the floor.
Full technique — 7 steps
  1. Sit on the floor and lean your torso back until you can balance on your buttocks.
  2. Lift both feet off the floor with legs straight and together, and hold your arms out to the sides.
  3. Tighten your stomach and keep your ribs pulled down.
  4. Exhale and bend your knees and hips to draw your knees toward your chest.
  5. At the same time, bring your torso more upright and reach both arms forward beside your knees.
  6. Extend your legs back out and open your arms under control, keeping your feet off the floor.
  7. Begin the next rep from the extended position without resting your feet or hands.

Common mistakes

  • Letting the lower back arch
  • Dropping heels between reps
  • Swinging legs with momentum
  • Leaning too far back and losing balance
  • Swinging arms for momentum

Form cues

  • Keep ribs down
  • Exhale pulling in
  • Reach legs long
  • Keep feet off floor

Substitutes by equipment

Same muscles, same movement — pick the version you have the gear for.

Dumbbells

Resistance bands

Medicine ball

Suspension trainer

Where to start and where to go next

Same muscles, same movement. Too hard for now — step down; once it gets easy — step up.

  1. Easier Ab Wheel Straight Arm Crunch 15% of bodyweight
  2. Easier Reverse Crunch 25% of bodyweight
  3. This exercise Seated Knee Tuck 30% of bodyweight
  4. Harder Ab Wheel Half Rollout 40% of bodyweight
  5. Harder Ab Wheel Knee Tuck 60% of bodyweight

Too hard for now? Start with the Reverse Crunch.

Quick answers

What muscles does the Seated Knee Tuck work?

Primary: Abs 9/10. Also works: Obliques 5/10.

When should I do the Seated Knee Tuck in a workout?

Finisher. Goes last, once the heavy work is done. ≈ 5 min with rest.

How many sets and reps of the Seated Knee Tuck?

Strength: 3 sets of 10–12 reps, rest 1 min, 2–3 reps in reserve. Muscle growth: 3 sets of 12–20 reps, rest 1 min, 2–3 reps in reserve. Endurance: 2–3 sets of 20–30 reps, rest 45 s, 3–4 reps in reserve.

What can I do instead of the Seated Knee Tuck?

Dumbbells: Dumbbell Decline Sit-Up, Dumbbell Straight Arm Crunch. Resistance bands: Lying Resistance Band Crunch, Lying Resistance Band Knee Tuck. Medicine ball: Medicine Ball Toe Touch Crunch, Medicine Ball Straight Arm Crunch. Suspension trainer: Suspension Trainer Hanging Knee Raise, Suspension Trainer Hanging Leg Raise.

What is an easier version of the Seated Knee Tuck?

Reverse Crunch (25% of bodyweight), Ab Wheel Straight Arm Crunch (15% of bodyweight).

What is a harder version of the Seated Knee Tuck?

Ab Wheel Half Rollout (40% of bodyweight), Ab Wheel Knee Tuck (60% of bodyweight).

How we rate exercises

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