How To Do Crunches (That Aren’t Bad for Your Back)

Many trainers hate crunches because they represent the false idea of spot training – the myth that feeling your abs burn means burning more belly fat. Trainers also hate crunches because they represent inefficient training and simply not knowing what you’re doing. You can’t go into a gym and not see people flailing around on the ground for endless reps while yanking their head forward and thinking they know how to exercise.

Stack all that on top of the fact that people sit in a forward flexed position all day then come to the gym and repeatedly flex forward doing crunches and you can see why many trainers cringe when they hear the word “crunches.”

Crunches represent almost everything trainers think is wrong with mainstream fitness practices in one exercise.

How to Do Crunches for Abs the Best Way

I don’t program standard crunches, but not because I think they’re bad. I just prefer spinal flexion abs exercises that allow you to train through a larger eccentric range of motion, such as crunches on a stability ball where you stretch over the ball at the bottom of each rep. (After all, I’m not going to do biceps crunches instead of full-range biceps curls.)

Here’s a detailed tutorial of what I call Stability-Ball Plate Crunches, which is one of my staple abdominal exercises.

You can also do this on a Bosu or on an Ab Mat to increase the eccentric stretch at the bottom of each rep.

As you can see in the video, this exercise provides a sufficient training stimulus to get stronger abs without the endless reps, which is also why I don’t use traditional floor crunches. I also use spinal flexion exercises in conjunction with anti-spinal movement exercises because I think each type of exercise (static and dynamic) offers unique benefits that combine for complete core strength.

Are crunches bad for your back?

Are crunches better than sit ups?

Are crunches good for athletes?

Are crunches bad for your posture?

Are crunches effective for abs?

Over the years, we’ve gone from doing sit-ups, to crunches to anti-flexion exercises for abs.

I’m all about the relentless pursuit of finding the most effective and safest methods to train. I agree that crunches are safer and more effective than sit-ups. However, I think the trend of exclusively using anti-spinal flexion exercises is an over-correction to poor abdominal training practices, such as the overuse of sit-ups or endless reps of floor crunches and the related ab crunch variations such as bicycles, side crunches, etc. And, I also don’t think the common idea that spinal flexion exercises, like the stability-ball pate crunch (I demonstrated above) are somehow inherently injurious has nearly as much merit as many trainers commonly believe.

That said, after seeing that I’m a proponent of spinal flexion resistance exercises like the Stability-ball crunch, I’m always met with the same questions and concerns from well-meaning trainers about spinal flexion exercises being inherently bad for your back, bad for your posture, non-functional, etc.

To help you better understand my thought process and rationale behind the use of spinal flexion exercises for abs like the stability-ball plate crunch, below I’ve provided my direct responses to many of the common concerns and arguments against spinal flexion exercises that many trainers have. This way you can see why I simply don’t find these arguments compelling enough to ride the anti-spinal flexion exercise bandwagon.

I’ve not repeated any of the great points that have already been made in other great, research-based articles about crunches HERE, HERE and HERE.

Let’s get into it!

“Dr. Stuart McGill Says Crunches Bad for Your Back”

Many trainers want to claim that spinal flexion exercises like stability-ball crunches and reverse crunches are universally dangerous, which they believe is a claim based on Dr. Stuart McGill’s research.

The following are two training recommendations taken from a 2017 paper on the crunch, co-authored by Dr. McGill:

• “If the ability to bear heavy loads is important to a client, it may be better to choose abdominal exercises with high muscular loads such as push-up position walkouts, rollout planks, or stir the pot. If flexibility is more important to the client, the personal trainer may want to select full-range curl-ups and crunches, and reduce heavy loading.” (1)
• “If maximal muscular development is the primary goal, including the crunch and/or its numerous variations, together with other exercises, may help to enhance desired results. However, personal trainers should consider the entire exercise program, including cumulative tissue loading considerations and weigh the tradeoff between mobility and load-bearing ability.” (1)

I highly doubt Dr. McGill would ever recommend the use of crunches and other spinal flexion ab exercises if he genuinely thought they were inherently dangerous.

In fact, research has shown that spinal flexion exercises can not only help promote nutrient delivery to the intervertebral discs, but may also provide superior muscle and performance gains versus isometric ab exercises (2).

The main takeaway here is that spinal flexion resistance exercises for abs are no different than any other resistance training exercises. Some exercises may be contraindicated for people who have pain when performing them.

All exercises can induce stress, which causes tissue adaptation. Loading enhances tissue resiliency in general, but there’s a tipping point when you exceed your capacity. That’s the individual nature of training, and exactly what’s meant by training smart!

Exercises are general, but exercisers are individual. So, I don’t think everyone has to do stability-ball plate crunches or other spinal flexion exercises. I just don’t think spinal flexion resistance exercises are universally dangerous to where they should be automatically eliminated as an option. I think they should only be eliminated if an individual is unable to do them with control and pain-free.

“Crunches Cause Bad Posture”

If you believe doing crunches will cause you to have a more flexed posture because that’s the movement involved in the exercise, then you must also believe that doing Romanian deadlifts will lock you into spinal extension and hip extension since that’s involved in the exercise.

The stability-ball plate-crunch is my go-to spinal flexion exercise because it allows for greater abdominal muscle stretch than floor crunches. This is important because full-range resistance training regimens, which train the muscles at long (stretched) lengths and include an eccentric component, can improve flexibility as well as, if not better than, typical static stretching.

In other words, strength training at longer (stretched) muscle lengths (that includes an eccentric component) not only causes muscles to be stronger at long lengths, but also promotes flexibility by causing muscle fibers to produce new sarcomeres in series within a muscle, which allows the muscle to lengthen more (3, 4).

In short, not only will you NOT cause a muscle to adaptively shorten if you’re lengthening it (eccentrically) under load, doing so will improve the functional length of the muscle better than typical stretching.

“Core Stability Exercises Are More Functional”

I’ve heard it stated that the abs are “primary designed to resist motion.” I’d say it’s more accurate to say that the abs are primarily designed to be able to respond to the task at hand. Sometimes that task requires them to resist motion isometrically, and other times that task requires them to create motion dynamically. Hence why the abdominals can do both, resist unwanted spinal extension and also effectively create spinal flexion.

Heck, if your abs were “primarily designed” to control spinal flexion, they’d never be so great at creating spinal flexion.

That said, many trainers choose to perform anti-spinal movement exercises to train the abs and they avoid spinal flexion exercises because they feel it’s more functional for sports. They often call anti-spinal movement exercises like planks and plank variations “stability exercises,” but they’re really just isometric exercises.

The funny thing is, trainers and coaches don’t call isometric biceps curls “elbow stability training,” nor do they call isometric squats “knee stability training.” That logical inconsistency aside, there are limitations of isometric training for performance because the strength gains it produces are extremely joint-specific and they transfer to those specific positions better. (5,6,7,8,9,10,11,12)

Sure, anti-spinal movement exercises are great for helping to improve the function of the trunk musculature; it’s the ability to remain stiff in order to transfer force between the hips and the shoulders. However, the torso doesn’t just transfer force and reduce force by limiting movement. It also helps produce force by creating motion. (13)

From MMA to tennis, you can’t deny the obvious active movement role of the trunk in power production (force summation) during sporting events. Try to imagine Serena Williams serving a ball without moving her torso. You can also appreciate the active movement contribution the torso has in power production by trying a simple experiment.

First, perform an overhead soccer medicine ball throw. Use a medicine ball that’s about 4-6 pounds. Then do it in the standard athletic fashion, where you extend at your spine and hips a bit (don’t go to end range) in order to allow your (anterior) torso musculature to eccentrically load. Got that?

Then compare that to an anti-extension soccer-style throw where you don’t allow your spine to move at all. You already know which of the two throws will be more powerful, not to mention which throw will feel more natural and athletic.

So based on what the principle of specificity dictates (and barring any injury), it makes the most sense to train both anti-spinal movements and active spinal in order to maximize your strength and performance.

“Crunches Aren’t Good for Athletes”

When I first started as a trainer in the late 90s, I came up during the functional training trend. It was all about doing integrated, 3D exercises from your feet, which certainly does have some merit. However, just because an exercise is from the ground and targets a specific muscle group, doesn’t mean it fails to offer positive transfer to standing performance.

That said, as a way to “prove” that ab exercises from the supine position, like crunches or stability-ball plate crunches, were “non-functional”; it was common for functional training proponents to claim that the abs don’t flex your spine from standing. The practical implication was doing supine, spinal flexion based exercises targeting the abs doesn’t offer transfer to improve standing sports performance.

I debunked this in a Core Training course I did over a decade ago. Watch this video:

“US Army Research Says Core Stabilization Exercises Work Better for Sit-Up Performance and Are Safer”

In 2010, there were two studies published looking at army soldier sit-up performance and back pain rates comparing traditional sit-up training to “Core Stabilization exercises.”

Both papers were based on the same workout program comparison, just each paper focused on a different outcome. They concluded:

• The Core Stabilization Exercise Program (CESP) did not have a detrimental impact on sit-up performance or overall fitness scores or pass rates. There was a small but significantly greater increase in sit-up pass rate in the CSEP (5.6%) versus the Traditional Exercise Program (TEP) group (3.9%). (14)
• There was marginal evidence that the CSEP resulted in fewer days of work restriction for low back injuries. (15)

I’ve encountered countless trainers who think these papers provided the knockdown argument against the use of spinal flexion ab exercises… since the results of these two studies suggest that performing core stabilization exercises in lieu of traditional sit-ups did not have a negative impact on either performance or passing rates for the sit-up test, and potentially were associated with less low back injury.

I don’t think these studies provide any argument against the use of crunches because CRUNCHES WERE USED as one of the “Core Stabilization Exercises.”

The traditional Army sit-up workout program absolutely sucked, but that’s not the point here.

I don’t think you can take studies that demonstrated GREAT RESULTS using a spinal flexion exercise (draw-in crunches) and try to claim these studies show spinal flexion exercises are inherently not good.

Baxter et al. (16) also observed no decrement in sit-up performance among a small cohort of US Military Cadets at West Point who exclusively performed abdominal crunch exercises during a 6-wk training period.

Now, the explanation for why soldiers in these studies most likely got the results they did is simple!

Numerous studies have shown the abdominals flex the spine for about the first 30 to 45 degrees of movement which is approximately equivalent to lifting your shoulder blades off the ground (17,18), which is the standard range of motion for a crunch. Beyond 30 degrees (the ankles between your back and the floor after lifting your entire shoulder blades off the ground, it’s commonly thought the hip flexors begin to take charge of the movement, which increases spinal compression loads without increased abdominal muscle activation (19)

Plus, pulling the abdominals in while in a supine position with bent knees – the draw-in crunch was used as the first exercise – may be an effective means of helping to bring your rib cage and pelvis towards one another, maximizing the effect of the crunch. (18)

This explains why their abs got stronger to have better sit-up performance even though they didn’t do sit-ups in training. And, since they weren’t doing so much redundant volume of sit-ups as is involved in the traditional training group program, they were getting as much overuse in the same movement pattern.

It’s important to note that the crunch involves about  3-degrees of lumbar flexion (19), which is less likely to result in increased forces across the lumbar disc relative to the 15-degrees of lumbar flexion in a full bent-knee sit-up, and the 6 degrees in the long-lying sit up. (19)

“Spine Sparing Exercises are Safer”

Research has shown the basic crunch elicited around 2,000N of compression on the spine at L4/L5 (8). It’s because of that level of spinal compression that many trainers say those exercises should be avoided. However, many of these same trainers will proudly recommend exercises like kettlebell swings and bent-over rows.

Interestingly, spinal loading at the beginning of the swings when using a 16kg kettlebell created 3195N of compression, 2328N at the middle of the swing, and 1903N of compression at the top of the swing (9).

And the bent-over row was shown to create 3,576N on the spine, which is also significantly higher than the compression created on the lumbar spine during a basic crunch (10). So, as Bret Contreras said, “Many coaches vilify certain exercises based on the levels of spinal loading they produce only to prescribe alternative exercises that exceed the levels reached in the exercises they discourage.”

Now, some will argue by saying that crunches involve spinal flexion, which is the problem, but the kettlebell swing and the bent-over row don’t involve any lumbar flexion. They say to just keep your spine in a safer position to deal with these levels of compression. Unfortunately, this common belief has also been falsified in multiple studies.

There’s a multitude of research showing that lumbar flexion occurs when performing a variety of common lifts, even when lifters are cued to maintain a neutral spine while under the watchful eye of experts such as Dr. Stuart McGill:

Two studies on squats using men and women found that in every case, as soon as a loaded bar was placed across the rear shoulder region prior to the commencement of the downward phase of the squat, the lumbar spine lost its normal or natural curve (24,25).

Another soon to be published thesis paper titled, “Lumbar spine kinematics and kinetics during heavy barbell squat and deadlift variations,” out of the University of Saskatchewan, showed 50% and 80% max flexion on squats and deadlifts respectively.

It’s impossible for the lumbar to stay in spinal neutral (which is more of a range than a specific spinal position). That’s nothing new, as it was demonstrated by biomechanists in 1994 (26). Note how it looks neutral but it’s still flexed.

It looks neutral despite it being 22 degrees of lumbar flexion, which is around 35% of max flexion (27). Researchers suggest that what appears to be a neutral-looking lumbar spine position (when it’s actually flexing) is in reality the thoracic spine being more neutral (28).

Another reason could be due to normal human variations in pelvic shape, which makes it difficult to accurately determine pelvic posture. Research shows there’s considerable morphological variation between pelvises. It’s possible that differences of up to 23 degrees in the ASIS-PSIS angle (and 22 degrees in the pubic symphysis-ischial spine angle) could reflect differences in morphology rather than differences in muscular and ligamentous forces acting between the pelvis and adjacent segments (29).

This isn’t at all saying there’s no need to coach or attempt to maintain a stiff, lordodic lumbar position when you perform these types of exercises. You certainly want to attempt to control your spine and maintain the strongest position you can because you can change the amount of lumbar flexion a little.

It’s simply highlighting the fact that some level of lumbar flexion is unavoidable, even when you’re trying to actively prevent it. And some level of lumbar spine flexion is going to occur no matter what. You can’t accurately call lumbar flexion a reliable risk factor to avoid when it’s a normal and unavoidable aspect of many functional movements and common lifts.

I’ll grant that if you want to do all you can to help improve the strength of the core muscles to transfer force by limiting trunk movement, you’ve got to use some isometric core exercises. However, if you really want to do all you can to help improve core strength, you’ve got to also add in some dynamic core exercises.

“Just Do Heavy Squats and Deadlifts, Bro!”

A few studies have taken the position that multi-joint, free-weight exercises such as barbell squats and deadlifts activate “core” muscles better than isolation core exercises.

These studies have led many trainers, coaches and exercise enthusiasts to mistakenly think that you don’t need to do exercises that focus on strengthening your abs and obliques because squats and deadlifts do the job more effectively.

The truth is, when you look at the evidence, the common claim that “heavy squats and deadlifts are all you need to strengthen your abs and obliques,” doesn’t make sense. In fact, the common push-up activates the abs and obliques more than squats or deadlifts!

A Closer Look at the (Misinterpreted) Science

One of the two studies that are most commonly quoted as scientific “evidence” that squats and deadlifts work better for strengthening your abs and obliques is entitled Systematic Review of Core Muscle Activity During Physical Fitness Exercises.

The purpose of this article was to “systematically review the literature on the electromyographic (EMG) activity of 3 core muscles (lumbar multifidus, transverse abdominis, and quadratus lumborum) during physical fitness exercises in healthy adults.”

(You scientific detective types will notice that when the authors say “core muscles,” they’re not referring to the rectus abdominis and the obliques.)

The major findings of this review were as follows:

• Moderate levels of evidence indicate that lumbar multifidus EMG activity is greater during free weight exercises compared with ball/device exercises and is similar during core stability and ball/device exercises. (30)
• Transverse abdominis EMG activity is similar during core stability and ball/device exercises. (30)

It’s clear that the results of this review certainly don’t demonstrate that squats and deadlifts create more activation of the rectus abdominis and oblique musculature than exercises that focus on those core muscles.

However, what these findings do tell us is if you’re doing exercises like squats and deadlifts, you’re not neglecting the deep (local) core stabilizing muscles like the transverse abdominis and the lumbar multifidus.

The researchers concluded that, “The available evidence suggests that strength and conditioning specialists should focus on implementing multi-joint free weight exercises, rather than core-specific exercises, to adequately train the core muscles in their athletes and clients.” (30)

Now, if you only read that conclusion, and failed to ask, “Which core muscles did the researchers of this study look at?” you can clearly see how the study was misrepresented as demonstrating that squats and deadlifts create more abdominal activation than core-focused exercises directed at those specific muscles.

Not Even as Good as a Push-Up

Another study that often gets misrepresented is entitled Trunk Muscle Activity During Stability Ball and Free Weight Exercises.

In it, squats and deadlifts were done with loads of approximately 50, 70, 90, and 100% of the subject’s 1RM. Subjects also completed 3 stability ball exercises: birddog, hip bridge, and ball back extension.

The findings:

• No significant differences were observed in the rectus abdominis and external oblique muscles during any of the exercises. (31)
• Activity of the trunk muscles during squats and deadlifts is greater or equal to that which is produced during the stability ball exercises. Squats and deadlifts are recommended for increasing strength and hypertrophy of the back extensors. (31)

In short, this study showed that squats and deadlifts elicit high levels of activation in the posterior core muscles (i.e., the back extensors) when compared to other exercises that target the posterior core muscles.

But they didn’t compare squats and deadlifts to exercises that are designed to activate the anterior core (abdominals and obliques) musculature.

Additionally, the following graphs (32) help give you a visual of just how much or, more accurately, how little the anterior core muscles are activated during squats and deadlifts as opposed to other anterior core-specific exercises.

As you can see, according to this research, squats and deadlifts don’t even come close to creating the levels of activation in the rectus abdominis that the push-up does.

Likewise, the graph below (32) shows that squats and deadlifts create higher levels of muscle activation in the external obliques than they do in the rectus abdominis. However, the level of external oblique muscle activation is still well below that created by the push-up!

So, if you seek to have truly strong abs, it requires targeted exercises for your abs.

References:

1. Stuart Mcgill, PHD. Brad Schoenfeld, PHD. Choosing Exercises – “The Crunch”. Personal Training Quarterly Journal. Volume 4, Issue 2. National Strength and Conditioning Association – 2017. 
2. Schoenfeld BJ, Morey J. Abdominal crunches are/are not a safe and effective exercise. Stren Cond Jour. 2016 Dec;38(6):61-4.
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25. McKean, Mark & Burkett, Brendan. (2012). Does segment length influence the hip, knee and ankle coordination during the squat movement?. Journal Fitness Research. 1. 23-30.
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29. Preece, S. J., Willan, P., Nester, C. J., Graham-Smith, P., Herrington, L., & Bowker, P. (2008). Variation in pelvic morphology may prevent the identification of anterior pelvic tilt. The Journal of manual & manipulative therapy, 16(2), 113-7.
30. Martuscello JM, et al. “Systematic review of core muscle activity during physical fitness exercises” J Strength Cond Res. 2013 Jun;27(6):1684-98.
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32. New Training Techniques. Powerpoint presentation by Jeffrey M. McBride, PhD Associate Professor – Biomechanics Department of Health, Leisure & Exercise Science Appalachian State University, 2006.