Muscles worked
In the seated knee tuck, your knees and chest meet in the middle. Your hip flexors pull your knees in, and the rectus abdominis curls your body so your pelvis and ribcage move towards each other. Many people feel it most low down in the abs. As your legs extend again the same muscles brake, and your abs work to stop you falling backwards. Your arms are only there for balance. The straighter your legs go on the way out, the heavier each rep.
Common mistakes
- You hang on your arms. If you lean far back and carry your weight with your hands, the work moves to your shoulders. Lean back only enough for your feet to lift, and let your hands support you lightly.
- Your feet land on the floor between reps. Every time your feet rest, your abs let go. Keep your feet in the air for the whole set, and do fewer reps rather than rest halfway.
- Your legs only go halfway out. Short reps are quicker but give less work. Extend your legs until they are almost straight every time, so your abs work through the whole movement.
Variations and alternatives
- The hanging knee raise is a harder step, where you hang from a bar and raise your knees with no support.
- The reverse crunch is done lying on the floor and works when there is no bench.
- The V-sit hold holds a similar position still, when you want to train your abs statically.
Sets and reps
Two to three sets are plenty, with 10 to 20 reps in each and a minute's rest. Pause for a second when your knees are closest to your chest and extend your legs over two seconds. Check that the bench is stable before you start. The guide to sets and reps helps you find the right number for your goal.
Once 20 reps feel easy, lift your hands slightly off the bench or extend your legs even more slowly. Making each week a little harder than the last, in small steps you can repeat, is the basis of progressive overload. How many sessions a week suit you is explained in the guide to how often to train.