Most abdominal exercises are recommended based on their ability to work your abdominal muscles.
However, while some exercises may be good for your abs, they also have the potential to be bad for your back.
You may know someone whose back “just went” while they were in the middle of a simple everyday task – picking up a pencil from the floor, lifting a bag from the car, or even just sneezing.
“Very few back injuries, however, result from a single event,” says Professor Stuart McGill, an expert in spine function and injury prevention at the University of Waterloo in Canada.
Instead, most injuries to the lower back are the result of damage accumulated over time.
And the event that appeared to cause the injury was – no pun intended – simply the straw that broke the camel’s back.
All of which brings me to the sit-up.
The sit-up is an effective exercise for anyone who wants to train both the abdominals and hip flexors. However, it’s also been shown to impose extremely large compression forces on the discs in your spine.
In a laboratory setting, McGill and his colleagues have shown that one of the quickest ways to damage these discs is to load the spine while repeatedly bending it back and forth .
Which is remarkably similar to what happens during the sit-up.
“The US National Institute of Occupational Safety and Health has set the action limit for low back compression at 3300 N; repetitive loading above this level is linked with higher injury rates in workers,” explains McGill in his book Low Back Disorders.
“Yet this is imposed on the spine with each repetition of the sit-up!”
Repeated spinal flexion also has the potential to cause more damage if it’s done first thing in the morning.
You’re taller when you wake up in the morning than when you go to bed at night. That’s because the discs in your back are hydrophilic. In other words, they suck up water while you sleep.
First thing in the morning, these discs are like a balloon full of water.
If you do a lot of bending (such as sit-ups or touching your toes), there’s a lot of stress on those discs.
In fact, the stresses associated with early morning bending exercises are roughly three times higher than when you perform the same exercise two or three hours later.
“Researchers have documented the increased annulus stresses after a bout of bed rest,” says McGill.
“Yet many athletes and laypeople alike get up in the morning and perform spine stretches, sit-ups, and so on. This is the most dangerous time of day to undertake such activities.”
In fact, if you’re suffering from back pain, one of the best things you can do is to cut back on the amount of bending you do first thing in the morning.
Some evidence for this comes from research published in the journal Spine . The study shows that controlling lumbar flexion in the morning is an effective way to reduce back pain.
A group of 85 subjects with persistent or recurring low back pain was assigned to one of two groups.
One group was told to restrict the amount of bending they did in the early morning. The control group received a “fake” treatment consisting of six exercises shown to be ineffective in reducing low back pain.
After six months, back pain was reduced in the group told to restrict bending activities in the early morning.
A follow-up study shows that participants who continued to restrict bending activities in the early morning enjoyed a further reduction in back pain .
After you get up, just walking around helps to “squeeze” the fluid out and compress your spine. If you want to do your ab workouts early in the day, wait for an hour or two after getting out of bed.
One of the criticisms of McGill’s work is that some of his research has been done using the spines from dead pigs, which obviously aren’t the same as the spines found in a living human.
However, as McGill points out in his book Low Back Disorders, “healthy human spines are extremely rare. Typical donors are elderly and sick or had sustained substantial violent trauma. Obtaining matched young, healthy human specimens for controlled study simply is not a reality.”
While pig spines might not be the perfect solution, they are biomechanically similar to the human spine and provide, at the very least, a reasonable idea about what’s going on.
Check out this extract from Low Back Disorders for more information on the subject.
Doing sit-ups with bent rather than straight legs is often recommended as a way to take the stress off your back. But when testing the idea, McGill found very little difference in lumbar spine compression when sit-ups are done with the legs bent versus straight.
Of course, there may very well be a guy at your gym who’s been doing sit-ups every day since 1996, and his back seems just fine thank you very much.
The fact that someone has done sit-ups their whole life without any apparent back problems doesn’t automatically mean that we should all be doing them.
For one, how many other people have done the same thing but ended up with a bad back?
There may very well be a much larger pool of people who did a lot of sit-ups and are now sat at home every night.
They’ve stopped going to the gym, mainly because their back hurts.
But you won’t ever get to hear their side of the story.
Mr Sit-up may have been born with a type of spine that is more resilient than most.
Individual genetic variations mean that people have different shaped discs, which affects the type and amount of stress your back can tolerate.
Sit-ups may not damage your spine right away. But each set could be moving you one step closer to a crippling back injury that keeps you out of the gym for some time.
An exercise is a tool used to generate a specific training effect.
In most cases, the best exercise to choose is the one with the greatest benefit-to-risk ratio.
As the old investment cliché goes, it’s all about maximizing the upside while minimizing the downside.
There are exercises out there that train the same muscles as the sit-up, but with less risk of tissue damage.
In other words, you’re actually getting a more challenging workout for your abs without increasing the risk of a “bad back” further down the line.
That’s not to say you should ditch every single ab exercise that involves lying on your back. During his work with patients suffering from lower back pain, Professor McGill developed an exercise that’s become known as the McGill Curl-up.
While it looks like a crunch, the McGill Curl-up will help you get a six pack while imposing a relatively small compressive load to your spine. In the video below, McGill explains how to perform the exercise at the 3-minute mark (this link takes you straight to the video at the correct start point).
Lie on your back with your left leg straight and flat on the floor. Your right knee should be bent to 90° with your right foot flat. This will help to preserve the natural “arch” in your lower back, also known as a neutral spine posture.
Place your hands under your lower back with your palms down. Again, this helps to keep your spine in neutral. Do not flatten your back to the floor, as this increases the loads on the disc and ligaments.
No cervical (upper spine) motion should occur, either chin poking or chin tucking. For anyone experiencing neck discomfort, place the tongue on the roof of the mouth behind the front teeth, which helps to promote stabilizing neck muscle patterns.
Brace the abdominals. This involves tightening the abdominal muscles as if you’re about to take a punch in the gut. When the brace is performed correctly, the abdominal wall is neither hollowed in nor pushed out.
Don’t pull in your abs. The usual advice is to “pull your belly button in toward your spine” or “pull your abs in” during the crunch. However, researchers have found that “pulling the abs in” actually reduces the mount of work done by rectus abdominis, also known as the six-pack muscle .
Curl up against the brace. Breathe deeply in the “up” position while maintaining the brace. Remain in the up position long enough to take a few deep breaths (6-8 seconds). Do not hold your breath but breathe deeply.
Make sure to raise ONLY your head and upper shoulders off the floor. The motion takes place in the thoracic spine – not the lumbar or cervical region.
The McGill Curl-up will challenge rectus abdominis while minimizing compressive load to the lumbar spine. Try it the next time you train your abs. You’ll be surprised at how such a simple exercise can easily be made more challenging and effective.
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ABOUT THE AUTHORChristian Finn is the nation’s leading authority on science-based, joint-friendly ways to build muscle. A former "trainer to the trainers," he holds a masters degree in exercise science, and has been featured in or contributed to major media on two continents, including the BBC and Sunday Times in the U.K. and Men’s Health and Men’s Fitness in the U.S.
1. Axler, C.T., & McGill, S.M. (1997). Low back loads over a variety of abdominal exercises: searching for the safest abdominal challenge. Medicine and Science in Sports and Exercise, 29, 804-811
2. Karst, G.M., & Willett, G.M. (2004). Effects of specific exercise instructions on abdominal muscle activity during trunk curl exercises. Journal of Orthopaedic and Sports Physical Therapy, 34, 4-12
3. Callaghan JP, McGill SM. (2001). Intervertebral disc herniation: studies on a porcine model exposed to highly repetitive flexion/extension motion with compressive force. Clinical Biomechanics, 16, 28-37
4. Snook, S.H., Webster, B.S., McGorry, R.W., Fogleman, M.T., & McCann, K.B. (1998). The reduction of chronic nonspecific low back pain through the control of early morning lumbar flexion. A randomized controlled trial. Spine, 23, 2601-2607
5. Snook, S.H., Webster, B.S., & McGorry, R.W. (2002). The reduction of chronic, nonspecific low back pain through the control of early morning lumbar flexion: 3-year follow-up. Journal of Occupational Rehabilitation, 12, 13-19