I did 70 starfish crunches every day for a week — here’s what happened to my abs

Two men doing straight leg crunches topless during ab workout
(Image credit: Shutterstock images)

Starfish crunches aren’t the sexiest of ab exercises to perform in the gym or during home workouts. You might feel a on show doing them, but boy do they fire up your core muscles.

I took to one of the best yoga mats to crunch through 70 reps of this ab exercise to see what I could learn from a seven-day dedicated core routine. And specifically, what would happen to my core muscles?

Here’s what happened, and why starfish crunches continue to surprise me.

How to do a starfish crunch

Let’s dissect the starfish crunch exercise:

  • Start laying on your back with your lower back pressed down into your mat
  • Extend your arms overhead behind you and your legs in front of you in a starfish shape
  • Engage your core and slightly tuck your pelvis under toward your spine
  • Lift your legs and arms toward each other at the same time, lifting your upper back off the mat and squeezing your abs
  • Pause, then slowly lower back down with control.

To make the move easier, lift one arm and the opposite leg together to meet in the middle and repeat on the other side, or add a soft bend to your knees and elbows. Moving with one arm and leg activates more of the oblique muscles used in rotational movement, and you could cross one arm to the outside of the leg for more twisting.

I did 70 reps of the starfish crunch exercise every day for a week — here are the results for my abs

Here’s how I found starfish crunches.

My abs, shoulder and hip flexors were set alight

Done properly, starfish crunches are a core exercise targeting the rectus abdominis (abs) and obliques. The movement pattern also recruits your hip flexors to help lift your legs and back muscles as you lift your arms and upper back.

Sure, my abs and shoulders kicked up a burn, but my hip flexors really switched on during this exercise. Strangely, despite being in the fitness industry, I haven’t tried this move before, and I’ll be adding it to the round-up of the best crunches and variations to focus more on. 

70 reps felt like a lot

I have pretty strong hip flexors and core muscles, so I found the movement comfortable, but it was still a lot harder than I anticipated and fired up more than just my core. This felt more like a full-body exercise and even raised my heart rate. 

I chose to do the reps in one go each day, but you could easily aim for sets of 10-12 reps or more. I can see why doing this core isolation exercise regularly could help you strengthen your ab muscles.

I added weights to progress the move

If you find starfish crunches difficult, I recommend lifting one arm and leg at a time until you build foundational strength. Once the exercise feels comfortable, you could add weights and move both arms and legs together. I've been a few variations, and many people classify the traditional starfish crunch as an alternating arm and leg core exercise. I chose a set of 2kg dumbbells, which helped to switch on my arms and shoulders more. 

I also tried out the ankle weights from the Pvolve workout kit, but I would only program clients to wear ankle weights for low-impact exercises like Pilates, as leg raises demand a lot from your hips.  

I had to focus more on my breathing

I’ve said it before — crunches labor my breathing, and despite banging on about the importance of breathwork to my clients, trunk flexion from a supine position prevents me from inhaling and exhaling smoothly. 

Ideally, try to exhale as your body meets the most resistance (the crunch itself) and save your inhale for lowering and resetting. Practice breathing with your diaphragm rather than into your chest.

I did 70 reps of the starfish crunch exercise every day for a week — verdict 

As a fitness trainer, I wasn’t under the illusion that a stacked set of abs awaited me at the end of this crunch exercise challenge. In fact, despite having a strong core, my stomach has always been a problem area. 

Shocker — no matter how super fit or healthy you are, some people are more likely to cling onto abdominal fat than others, and factors like genetics, stress and sleep all play into it, alongside your diet and exercise regime, of course. You can learn about calculating body fat percentage here. 

But for me, this wasn’t, and isn’t, about aesthetics. I love pushing my body to new limits and seeing what it teaches me. And this one? Well, I’m not great at crunches and prefer lifting heavy weights, but undeterred, I sucked it up and got to work. 

It was tough but not life-changing, and I recommend adding resistance to starfish crunches if you need a bigger challenge. That said, it’s a brilliant core exercise to add to your routine, and my body feels adequately torched. Job done then, I guess?

More from Tom's Guide

Sam Hopes
Senior Staff Writer - Fitness

Sam Hopes is a level III qualified fitness trainer, level II reiki practitioner, and senior fitness writer at Future PLC, the publisher of Tom's Guide. She is also about to undertake her Yoga For Athletes training course. Having trained to work with mind and body, Sam is a big advocate of using mindfulness techniques in sport and fitness, and their impact on performance. She’s also passionate about the fundamentals of training and building sustainable training methods.  When she's not writing up her experiences with the latest fitness tech and workouts, you’ll find her writing about nutrition, sleep, recovery, and wellness.