In the 1980’s and 1990’s, nearly everyone in the fitness industry was not only recommending crunches, they put the crunch on a pedestal and described the exercise with superlatives. I remember reading one of Dr. Frederick Hatfield’s books many years ago, where he said, “The crunch is the Cadillac of abdominal exercises.” Well, I would have said “Mercedes of ab exercises,” but you get the point – he was suggesting that crunches were the best vehicle to develop your abs… Are they? Let’s take a closer look…

Muscular man doing abdominal crunches in gymCrunches, the experts explained back in those days, were the ultimate ab exercise because the crunching movement – shortening the distance between the sternum and pelvis – is literally the primary function of the rectus abdominis muscles. This is also known as spinal flexion.

The crunch was also lauded because it was not a full sit up, which also activated the hip flexors, it was a simple short range of motion “curl up” that “isolated” the abs.

Then, Everything Changed And The “Anti-Crunch Era” Began

By the first few years of the new millennium, there was a huge shift in thinking about the crunch and about abdominal training in general.

What happened? Well, the fitness industry is notoriously fickle and prone to huge swings in opinion, even among legitimate experts, and we know all too well that consumers love to jump on the “latest and greatest.”

In this case, the big new trend was “core training” and when that fad took off, it was the end of the crunch era. Planks became the new darling exercise, and we saw many books published about training your core, with not a crunch (or a sit up) in sight.

But wait, there’s more. It was not enough to change the most popular exercise to a new one, the powers-that-be had to bash the old one. Suddenly, the crunch was worse than inferior – it was “bad for you.”

Not long after core training became the top fitness trend, we began to hear reports that crunches could hurt your lower back. Mind you, this came from trusted trainers, who said this warning came direct from exercise science labs. They said that too much spinal flexion (crunches) could actually cause a disc injury.

Well, my six-pack seeking friends, I’m here to tell you that if you were among the many who ditched crunches completely or if you also jumped on the anti-crunch wagon, you may not have heard the whole story. In fact, you may be missing out on one of the best ab exercises – yes, crunching exercises (properly performed) are still one of the best and deserve a place in a well-rounded ab program.

The Truth About Crunches, Spinal Flexion and Low Back Pain

I know and respect many of the trainers who said you should avoid crunches and do planks instead. On one hand, they have some valid concerns about injury prevention as well as good program design. But overall, crunches are a great ab exercise and are actually one of the safer ones, as long as best practices are followed.

At the end of this article, I’ll give you a list of best practices for doing crunches and other spinal flexion exericses safely to reap all their benefits without the risks. But first, let me tell you about the scientific research on which the demonization of crunches was based.

Some of the research on spinal flexion and disc damage was performed by Dr. Stuart McGill.  McGill is like the Mack Daddy of spine biomechanics. He is so well respected, that anytime he speaks, a lot of trainers listen. It’s not surprising then that so many fitness professionals who followed McGill’s work immediately passed on these spinal flexion fears to their clients and readers, sometimes without putting it all in context. Context is everything in fitness.

The problem is, while the research did implicate repetitive lumbar flexion as a mechanism in disc herniation, one part that got lost in translation was that the studies were on pig spines, not human spines. Not only that, dead pigs. Seriously.

But don’t blame the researchers – it’s not like you can flex human spines thousands of times in a row just to see how long it takes before the discs pop or something snaps. (Would you sign up for that study?)

When this fact came to light, then we started to hear more trainers say, “Wait a minute, is it correct to extrapolate data from dead animal studies to living human beings in the gym?” Indeed, living tissue has circulating fluids and nutrients and it gets stronger with progressive exercise.

Another flaw in the way many trainers and fitness enthusiasts interpreted the animal research is that the repeated flexing was not even a fair comparison to the workload or workout structure that a real person might do in the gym. Thousands of nonstop bending cycles is an extreme stress (as imposed in those studies), a few sets of crunches for 15, 20 or 25 reps with breaks in between sets is a completely different “animal.”

On a similar note, how often you train the abs is something to consider. Research on continuous daily high volume spinal flexion can’t be compared fairly to real world workouts that are only done 2 or 3 times per week, with rest days in between. Muscular structures and spinal tissues are given time to recover in between workouts, alleviating some of the disc stress, and promoting the strengthening process.

Let’s Put Crunches in Context

Also, what if crunches aren’t the only exercise being done? What if stabilization exercises like planks are done in addition to crunches, not instead of them? And what if you are giving your core and trunk other types of progressive resistance challenges like front squatting, overhead pressing and so on? Where’s the evidence that says intelligent programming of the crunch exercise into a well-rounded training plan has more risk than benefit in humans?

There’s even more: Some of the research that implicated crunches as a risk for back pain or disc herniation didn’t even approximate the crunch exercise at all. In the crunch, the range of motion is small – only about 30 degrees of spinal flexion, where only your head and shoulders come up off the floor – so it’s the thoracic region of the spine that is flexing the most, not the lumbar region. The impact on the spine depends on which segment of the spine is flexing and through what range of motion.

Furthermore, most people believe that back injury and spinal degeneration is caused mainly by wear and tear, but several studies have found that genetics is also a factor predisposing some individuals to low back pain and injury. This may explain why some people can train even in risky ways and never get injured, while others seem to be following all the best practices and they still get hurt.

Although some lines of research did raise concerns about crunches and other spinal flexion exercises, at least when considered in the context of the dose and frequency, there’s plenty of other evidence that shows crunches can not only be done safely, they have a long list of benefits.

Some Research Even Suggests that Crunches Reduce Low Back Pain

It should be common sense that moving and exercising is good for you and makes you fitter and stronger. That goes for moving – and flexing – the spine as well as other muscles and joints. Spinal motion delivers nutrients to the spinal discs. Being a couch potato accelerates disc degeneration and this becomes more pronounced as you get older.

Even when there’s a risk to benefit ratio to consider when doing a particular exercise, the benefit of exercising with good form in realistic amounts almost always outweighs the risk of doing nothing.

There’s even research suggesting spinal flexion exercises might help reduce lower back pain. Lack of spinal flexibility is associated with increased low back pain. Resistance training is a form of active flexibility and joint mobility exercise, so many resistance exercises increase flexibility (through the normal range of motion), and may help reduce back pain for that reason.

A balance of flexion and extension also appears to help build a healthy back, which would mean doing low back extension exercises to complement the crunching exercises.

Plus, Crunches Directly Develop Your “Six Pack”

The crunch is also one of the best ways to bring out the “six pack” look. There’s a reason for that. Many variations of the crunch exercise directly work and strongly contract the rectus abdominis – the six pack muscles – to a greater degree than many popular “core” exercises.

Dynamic exercises that move your joints through their range of motion also have an eccentric component and produce more metabolic stress, and therefore, have a greater capacity to stimulate hypertrophy, i.e., make your six pack abs pop out more.

So while the plank exercise (a static contraction exercise) is an important one to include in a well-balanced training program, there’s good reason to believe that crunches might be better than planks for developing the “six pack” look.

Bottom Line: Are Crunches Bad For You Or Not?

If we want to extrapolate the research to the real world, here’s what it’s probably telling us: That a high volume of daily ab work that involves a lot of the same spinal flexion exercises, or accumulating hundreds or thousands of repetitions every week, (or subjecting your body to the equivalent nonstop stress at work or doing physical labor), could increase the risk of low back injury.

I don’t believe the research supports the notion that crunches are universally bad for you. Taking all this into consideration, I would say the warnings about crunches and low back pain were premature and mostly unwarranted.

However, crunches and spinal flexion exercises can indeed be misused and overused, so there are handful of best practices you should know about to manage the risks.

Abdominal Training Best Practices For Spinal Flexion Exercises

1. Don’t do extremely high repetitions.

Doing hundreds of reps, let alone thousands, is not a good idea. Experts in spine biomechanics estimate that limiting to approximately 60 reps of spinal flexion exercises per workout is a sensible guideline. I admit I’ve done more than 60 reps in a workout myself, but not many more (maybe 100 or so when I did two crunching exercises in one workout, like floor crunch and a cable crunch). The main idea is to think quality, not quantity. Use additional weight to boost strength and hypertrophy rather than train for crunches for endurance.

2. Choose the right training frequency (Don’t train abs every day).

Doing abs – at least dynamic spinal flexion exercises – every day may also increase risks. All muscles require recovery between workouts and the abs are no exception. Allow at least 48 hours between dedicated ab workouts. Allow up to 72 hours if more recovery time is needed.

3. Balance your flexion and extension exercises.

If you do a lot of crunches, perform the opposite movement as well. That includes the low back extension and other posterior chain exercises.

4. Use a controlled repetition speed.

There are some studies that show faster reps, since they recruit more fast-twitch muscle fiber, can increase muscle growth. Faster reps may have more functional carryover for athletes as well. There are also reasons one might do slower reps, such as increasing time under tension and metabolic stress, which also can increase hypertrophy. A mix of rep speeds might be optimal and it may depend on the exercise. The down side of fast reps for ab training is that quick reps often use momentum, not muscle contraction, and are sloppily performed, thereby decreasing effectiveness and increasing risk of injury. The best practice for spinal health is to keep reps controlled and focus on squeezing and contracting the muscle.

5. Don’t train abs early in the morning right after you get out of bed.

Research has shown that spinal discs absorb more fluid while they are unloaded during sleep. Fluid leaves the disc as the day goes on and the spine becomes more elastic and flexible. Risk of disc injury then, is more likely when you train right after waking up. A lot of people train first thing in the morning, but doing spinal flexion exercises within one to two hours of waking carries more risk than doing them later in the day. If you must do your resistance training at the crack of dawn, don’t skimp on your warm up or joint mobility work and be cautious with high risk exercises.

6. Take heed of your genetics.

If you have reason to believe that you are genetically predisposed to low back pain, then take very careful note of everything that has been noted here as “high risk” and avoid the risky stuff.

In Upcoming Articles…

In upcoming posts, I’ll show you how to perform some of the most effective ab exercises, including the exact ones I used to prep for bodybuilding competitions. Be sure to bookmark this page, check back every Friday for the new weekly Burn the Fat Blog post, and subscribe to the mail updates. Until then,

Train hard and expect success!

Tom Venuto,
Author of Burn the Fat, Feed the Muscle: The Bible of Fat Loss

 P.S. Remember, you’ll never see your abs, no matter how hard you train, and no matter which exercises you do, if your abs are covered up with a layer of body fat. If you want to learn more about burning the fat off your stomach so you can see your abs, grab a copy of the Burn The Fat, Feed the Muscle…

You can pick up the Burn the Fat, Feed the Muscle Book at

Related: Stability ball crunches: A superior way to do the crunch exercise

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