Knee Ups: How to Perform, Muscles Used, and Alternative Exercises

The knee up is a fairly straightforward exercise that only requires the use of a flat bench.

Before you begin, make sure there's enough room around the bench. You'll need your feet to touch the floor in the start position and your arms to be slightly out to the sides when holding onto the back of the bench.

1. Lie with your back on a flat bench, feet on the floor. Make sure your head is close to the end of the bench, but not hanging off the back of it.
2. Bring your feet up onto the bench and place them flat on the surface with knees bent and touching.
3. Take your hands behind your head and grab the bench, one hand on each side, palms facing each other, not down. Your elbows will be bent.
4. Engage your core by drawing in your navel and contracting your abdominal muscles.
5. Contract your glutes and extend your legs into the air by lifting your hips/tailbone off the bench. Make sure to keep your abs contracted. Think about lifting through your heels and press your feet up towards the ceiling. The bottom of your feet should be facing the ceiling.
6. Point your toes in towards your shins. Pause, keep your abdominal muscles tight, and reverse the movement until your hips are touching the bench. This is now the starting position.
7. With your legs extending up, repeat the movement. Perform 2 to 3 sets of 10 to 12 repetitions.

A note about form: At the top of the movement, resist the urge to roll in towards your body. Also, make sure your form stays tight, and you do not sway forward and back or side to side.

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Make it easier

To make the knee up easier, decrease the distance between the bench and your hips during the initial part of the movement.

Make it harder

To make the knee up more difficult, consider using a decline bench. This puts your body at an angle and requires more balance and activation of your core muscles.

Additionally, to make this move harder, you can increase the distance you bring your hips off the bench.

The knee up is a very focused exercise that works the abdominal muscles. These muscles include:

• rectus abdominis
• external obliques
• internal obliques
• transverse abdominis

Since you contract the glutes to lift your hips off the bench, these muscles also get a workout.

When gripping the top of the bench for stability, you'll feel your arms, chest, and upper back tighten up. However, these muscles act as stabilizers. They are not the main muscles at work during the knee up.

Since the knee up requires you to lie flat on your back, pregnant women should avoid doing this exercise. Additionally, if you have any neck issues or low back pain, try a different exercise or ask a trainer or physical therapist to help you with the movement.

If you feel any pain during this exercise, stop what you're doing, and review the steps. Because of the position of your body, watching yourself do a knee up is next to impossible. To make sure your form is correct, consider asking a trainer for help.

Like many other exercises, the knee up is known by different names. Moves that are similar to the knee up — and work the same muscles — include:

• reverse crunch on a bench
• leg pull-in

If you're not quite ready for the knee up, or you're looking for other moves to strengthen your core, here are some exercises that specifically target your abdominal muscles:

• reverse crunches
• bicycle crunches
• planks
• flutter kicks

Strengthening and maintaining a healthy core is key to improving athletic performance, performing daily activities, and staying injury free.

Knee ups help strengthen the abdominal muscles, which are part of your core. You can perform the knee up individually, add it to a resistance training session, or include it in a comprehensive core workout.