Stop doing sit-ups! Try this one ab exercise for a rock-solid core

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I have made my feelings clear on sit-ups before — there’s a time and a place, but I can think of about 10 core exercises off the cuff that I’d rather do myself and program for clients. With that in mind, there’s one abs exercise I haven’t shared before, and it will build you a rock-solid core without putting pressure on your spine.

If, for whatever reason, sit-ups don’t agree with your body, scrap them and try this exercise instead. It builds an intense sensation in your stomach, requires stability and balance and hits the deeper core muscles that help stabilize your torso, which means it’s not just your abs getting stronger, but your core as a whole.

You will need a kettlebell, and I recommend a heavy one you can hold onto behind your head. If you don’t have one, any weight that you can secure in one place will work, or you could hold onto a heavy chair or sofa leg instead. One of the best kettlebells I would recommend is the TRX bell, but that’s just me!

What is the exercise?

This one is a combo of three exercises: your lower body resembles a single-leg deadbug while you perform a reverse crunch mixed with leg raises. You could call it a deadbug reverse crunch or deadbug leg raises — whatever works for you. I recommend rolling out a yoga mat to support your body, but you don't have to use one, if you are comfortable with getting down on the ground.

How to do it

Lie on your back with a heavy weight placed behind your head that you can hold on to with both hands. Aim for a soft bend in the elbows with your arms mostly extended
Extend your left leg and bend your right knee, then bring your right leg into a tabletop position in the air
Slightly tuck your pelvis under to flatten your lower back to the mat or ground beneath you
Using your core muscles, lift your legs into the air toward the ceiling and raise your butt and lower back away from the ground, keeping a straight line between your left toes and shoulders
Slowly lower back down with control and repeat for 8-10 reps and 2-3 sets, switching sides halfway.

What are the benefits?

Deadbugs strengthen the deeper, stabilizing core muscles, like the transverse abdominal muscles, which act like a belt or corset beneath the abs that help stabilize your pelvis and spine. Drawing your belly button toward your spine can activate this muscle group, which is what you do during deadbugs.

For this variation, extend one leg, which will fire up your quads, hamstrings and hip flexor muscles, and remember to switch sides halfway through your reps. Raising your legs into the air in a mixed position like this will test balance and stability and work your core even harder.

Of course, lifting and lowering your legs while lying on your back resembles a familiar core exercise known as leg raises. Leg raises work the front body, namely the abs, hips and quads; depending on how flexible your hamstrings are, you might feel these muscles also activating throughout.

Unlike the standard crunch, where you draw your chest toward your thighs and lift your upper back away from the ground, the reverse crunch involves drawing your legs toward you while still focusing on the crunching motion and keeping your upper back supported — the distance between your chest and thighs decreases. As you crunch, focus on exhaling and squeezing your stomach muscles, and you will feel this move in all the right places.

All in all, there are many benefits to practicing this bodyweight exercise, including building a stronger core and creating a more stable torso. I recommend reducing the reps and sets until you feel comfortable with this move. For some, a set of ankle weights can ramp things up.

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Sam Hopes is a level 3 qualified trainer, a level 2 Reiki practitioner and fitness editor at Tom's Guide. She is also currently undertaking her Yoga For Athletes training course.

Sam has written for various fitness brands and websites over the years and has experience across brands at Future, such as Live Science, Fit&Well, Coach, and T3.

Having coached at fitness studios like F45 and Virgin Active and personal trained, Sam now primarily teaches outdoor bootcamps, bodyweight, calisthenics and kettlebells.

She also coaches mobility and flexibility classes several times a week and believes that true strength comes from a holistic approach to training your body.

Sam has completed two mixed doubles Hyrox competitions in London and the Netherlands and finished her first doubles attempt in 1:11.

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