The seated knee tuck is a bench core exercise that pulls the knees toward the chest while you lean back, loading the abs and hip flexors through a long range. Sitting on the edge of a bench lets the legs travel below the hips, so the movement starts further out than a floor crunch allows. It is a beginner-friendly accessory, and the bench doubles as the load control: the further you lean back, the harder the same rep becomes.
Muscles Targeted
- Primary: rectus abdominis, hip flexors (iliopsoas)
- Secondary: internal and external obliques, rectus femoris
- Tertiary: transverse abdominis, forearm flexors, quadriceps
Starting Position
Sit on the end of a flat bench with your hands gripping the edge just behind your hips. Lean your torso back to roughly 45 degrees, keeping the chest open and the lower back from rounding. Extend your legs out in front with the heels a few inches off the floor, and brace your abs so the hips carry the weight.
Execution Steps
- Brace your abs and take the weight of the legs onto the trunk before anything moves.
- Pull the knees toward your chest, curling the pelvis up rather than only folding at the hip.
- Lean the torso slightly forward as the knees arrive so the abs shorten fully.
- Squeeze at the top for a beat with the shins pulled close to the chest.
- Extend the legs back out slowly, leaning the torso back again as they travel.
- Stop with the heels just off the floor, then begin the next rep without resting.
Form Cues
- Curl the pelvis, not just the knees: tucking the tailbone under is what turns a hip movement into ab work.
- Keep the chest open: rounding the upper back moves the effort into the shoulders and neck.
- Hold the bench lightly, so the arms balance you rather than pull you.
- Exhale as the knees arrive and inhale as the legs extend.
- Keep your feet together throughout, which stops one hip from taking over.
Common Mistakes
- Swinging the legs: momentum carries the knees in and out while the abs stay slack for the whole set.
- Sitting too upright: an upright torso removes most of the range, and the exercise turns into a leg lift.
- Rounding the lower back hard: a heavily rounded spine under a long lever loads the discs rather than the abs.
- Pulling with the arms: yanking on the bench edge lifts your body instead of moving your legs.
- Letting the heels hit the floor: a rest at the bottom breaks the tension and shortens the working part of the set.
Variations
- Bent-knee tuck: keeping the knees bent throughout shortens the lever for a first attempt.
- V-up: taking the hands off the bench turns it into a full bodyweight movement.
- Hanging knee raise: the same tuck from a bar, with the shoulders under load as well.
- Weighted knee tuck: a light dumbbell held between the feet adds resistance.
- Roman chair knee raise: a back-supported version for lifters with a sensitive lower back.
Tips for Progression
- Lean back a few degrees further at a time to add load without adding weight.
- Build to 15 to 20 reps before adding a dumbbell between the feet.
- Add a two-second pause with the knees held at the chest.
- Slow the leg extension to three counts, since the return builds most of the control.
Training Notes
Use the seated knee tuck in a core block at the end of a session, for 3 sets of 12 to 20 reps with 45 seconds of rest. Two or three times a week is enough. It pairs well with a plank or a side plank, which train the trunk to resist movement while the knee tuck trains it to produce movement.