How many reps of the seated knee tuck should you do when you are new to the exercise?

Start with 2 sets of 10 to 12 slow reps, keeping the feet off the floor for the whole set. Once you can hold that for both sets without the torso sitting upright to cheat the fold, straighten the legs further on each extension before adding a third set.

What can I use instead of a bench for the seated knee tuck?

A sturdy chair edge, a low step, or a stair works the same way, as long as you can hang the hips slightly off the front edge. On the floor, sit with hands planted behind you for support and do the same lean-back-and-tuck motion without a raised edge.

What is the seated knee tuck good for, and who should choose something else?

It builds lower-ab and hip-flexor strength with a scalable balance challenge, and it is easy to progress just by straightening the legs. It is a poor first choice for anyone whose hip flexors already dominate their ab training, since a rushed tuck lets the hips do most of the folding instead of the abs.

Intermediate

Seated Knee Tuck

The seated knee tuck is a simple, scalable lower-ab builder you can do on any bench. Balancing on your sit bones with the torso leaned back, you pull the knees toward the chest and extend them out to fold and unfold the trunk against gravity. It pairs a strong lower-rectus and hip-flexor stimulus with a balance challenge, and it scales easily by straightening the legs.

Equipment: Bench
Body part: Abs
Type: Strength
Browse by muscle: Lower Rectus Abdominals, Rectus Femoris
Browse by movement: Spinal Flexion

How to do it

1
Sit on the end of a bench and grip the edge behind your hips for support.
2
Lean your torso back and extend your legs out in front, heels off the floor.
3
Exhale and pull your knees toward your chest while crunching the torso in.
4
Squeeze the abs at the point where knees and chest meet.
5
Inhale and extend the legs back out under control without touching the floor.
6
Keep constant tension by not resting the feet down between reps.

Tips

Fold the knees and chest toward each other so the abs, not just the legs, work.
Keep the movement smooth and avoid dropping the feet to rest at the bottom.
Straighten the legs more on each extension to make the exercise harder.

Variations

Common mistakes

The torso stays upright through the tuck instead of leaning back and crunching in, so the hip flexors do the folding while the abs barely engage.
The hands grip the bench edge so hard that the shoulders shrug up toward the ears, tensing muscles that have nothing to do with the lower abs.
Rushing the exhale-and-pull phase turns a controlled fold into a kip that uses momentum instead of the abs to bring the knees in.
The lower back rounds hard at the bottom of the extension instead of staying supported by the arms, straining the spine on the rep where fatigue is highest.
Speeding up near the end of the set to finish faster shortens the range at both ends, so the last few reps barely tuck or extend at all.

Frequently asked

How many reps of the seated knee tuck should you do when you are new to the exercise?: Start with 2 sets of 10 to 12 slow reps, keeping the feet off the floor for the whole set. Once you can hold that for both sets without the torso sitting upright to cheat the fold, straighten the legs further on each extension before adding a third set.
What can I use instead of a bench for the seated knee tuck?: A sturdy chair edge, a low step, or a stair works the same way, as long as you can hang the hips slightly off the front edge. On the floor, sit with hands planted behind you for support and do the same lean-back-and-tuck motion without a raised edge.
What is the seated knee tuck good for, and who should choose something else?: It builds lower-ab and hip-flexor strength with a scalable balance challenge, and it is easy to progress just by straightening the legs. It is a poor first choice for anyone whose hip flexors already dominate their ab training, since a rushed tuck lets the hips do most of the folding instead of the abs.

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