I did mountain climbers every day for a week — here’s what happened

a photo of a man doing mountain climbers
(Image credit: Getty/Morsa Images)

I have a love/hate relationship with mountain climbers (the ab exercise, not folks that climb mountains for fun!) — on one hand, they are a killer compound exercise that works your core, shoulders, back, hips, quads, and glutes with just your bodyweight. On the other hand, these hurt, and there’s a reason why I’ve put off this challenge for so long! But, in an attempt to really get to know the move, I unrolled my yoga mat, and decided to add 100 mountain climbers to my daily routine. 

With mountain climbers, you get a lot of bang for your buck. Not only are you hitting multiple muscle groups, but they’ll also get your heart rate up, and give you more of a full-body workout than other core exercises. They also force your core to work super hard to stabilize your body as you ‘climb’ your legs in and out. Is 100 a day the secret to a stronger core? Read on to find out. 

It goes without saying that 100 reps of any exercise are a lot and that if you are new to fitness, or returning to ab workouts following an injury, it’s a good idea to tread carefully. Always check your form with a personal trainer before adding reps (I did for this challenge), as they can take a look at your form, and give you pointers if you’re putting yourself at risk of injury. 

How to do a mountain climber 

an illo of a man doing mountain climbers

(Image credit: Shutterstock)

The easiest way to explain the movement involved in mountain climbers is that it's like running in a plank position. To do a mountain climber, start in a plank position, with your hands shoulder-width apart, your back flat, and your core engaged (think about sucking your belly button into your spine). From here, bend your left knee and bring it into your chest, as far as you can. Pause, then straighten your leg back to its starting position and bring your right knee in underneath your body. Keep repeating this movement and build up speed until you’re running your knees in and out. 

Here’s more on how to do a mountain climber, and the variations to try. 

I did 100 mountain climbers every day — here’s what happened 

Ready to find out what happened when I did 700 mountain climbers in one week? Read on. 

I had to get a PT to check my form

On day one, I opted for super-slow Pilates-style mountain climbers, where I almost paused as my bent knee reached towards my elbow. Moving slowly, my obliques were on fire by the end of my 100 reps, and I felt like I’d really worked my core hard. I also spent the reps thinking about sucking my belly button into my spine and keeping my hips still and glutes engaged throughout. This week will be a doddle, I thought. 

The next day, I decided to add my reps as a finisher at the end of a strength session in the gym. This time I opted to run my legs in and out, rather than stick to slow mountain climbers. A quick glance in the mirror showed me I was arching my back as I ran my legs back and forth, and tensing at my shoulders, giving me a horrible, hunched form. I videoed myself and sent the footage to a PT friend, who had some suggestions. Firstly, she told me to raise my arms, either onto a set of dumbbells, or yoga blocks, to create some more space and help me lengthen my arms. Secondly, she commented that, as a runner, I probably had super-tight hip flexors, and this could be another reason I was arching my lower back. Slow down, and think about your form, she advised.

I mixed things up

On day three, I worked on my form with the faster mountain climbers, doing five sets of 20 reps to give myself time to re-set each time. On day four, I grabbed my sliders and opted for sliding mountain climbers. These were an absolute killer, and left my core physically shaking after a couple of reps.  

an illo of a woman doing TRX mountain climbers

(Image credit: Shutterstock)

Day five, I decided to continue the torture, and grabbed a TRX band at the gym. If you’ve not tried it before, TRX suspension training is a full-body workout designed by a Navy SEAL, and has been found to build muscle and core strength. With my feet suspended in the handles, my core had to work hard to stabilize my body as I attempted to tuck one leg underneath my body, then the other. I only managed 50 before my burning core couldn’t cope, so did the final 50 as bodyweight mountain climbers. This was a real eye-opener, and a reminder that I should return to TRX training in the future.

On day six, I went for cross-body mountain climbers — This move is similar to a normal mountain climber, but as you bring you legs into your chest, you’ll angle it underneath your body, tapping your left knee to your right elbow. This one definitely worked my obliques harder than regular mountain climbers. 

Finally, by day seven, I was well and truly ready for this challenge to end, as I returned to the slow and steady Pilates climbers. 

I found it a lot more challenging than expected

This one was tough. Perhaps because I crammed so many variations into one week, but also because it really does work the entire body. I felt the mountain climbers in my arms as much as in my legs, and I really blasted my core. They also got my heart rate up most days, making them a great cardio exercise to add to a warm-up or finisher. 

I didn’t get a six-pack

Of course, a week is nowhere near long enough to make any physical changes, and visible abs are the result of a low body fat percentage, not endless mountain climbers (here’s how to calculate your body fat percentage, and why it matters). That said, my core felt like it had worked really hard, and I’ll definitely be using mountain climbers in future workouts. Who knows, perhaps one day I’ll make it to 100 reps on the TRX bands without collapsing onto the gym floor?

Looking for more workout inspiration? Here are the best ab exercises to add to your routine, plus the best 10-minute ab workouts for engaging your core and 5 yoga exercises that work your core

Check out what happened when I did 100 plank jacks every day last week. Plus, here are 5 yoga exercises that help you build a strong core.

Jane McGuire
Fitness editor

Jane McGuire is Tom's Guide's Fitness editor, which means she looks after everything fitness related - from running gear to yoga mats. An avid runner, Jane has tested and reviewed fitness products for the past five years, so knows what to look for when finding a good running watch or a pair of shorts with pockets big enough for your smartphone. When she's not pounding the pavements, you'll find Jane striding round the Surrey Hills, taking far too many photos of her puppy.