The problem is that most people, even those spending good money on a trainer, are doing exercises that are less than ideal. For example, have you been told do crunches instead of sit-ups because they put less strain on the back?
Although it’s true the sit-up compresses the lumbar spine (lower back) more than the crunch, both flex the spine under load, which we’ll find out later isn’t ideal for anyone trying to protect their back (1).
Others will tell you that the ‘core’ doesn’t need direct exercise and that movements like deadlifts and squats are all that you need to build and maintain a strong stable core.
Read on to see what gives.
What is the core?
Quite a few fitness professional don't like the term 'core' because it’s hard to pin down what are and aren’t core muscles, as most of the muscles of the torso can help stabilise the spine.
For the purposes of this article, the core includes the muscles that stabilise the thoracic and lumbar spine including the internal and external obliques, the rectus abdominus ('abs') the transverse abdominus, psoas major and minor, quadratus lumborum, and the spinal erectors.
These key muscles are shown below, but other muscles can also help stabilise directly, or help to increase tension in core muscles.
Pretty much all skeletal muscles can help us to move, but many of the muscles of our core are also very well suited to keeping things stable.
By that I mean that they are well-suited to stabilising our spine, and sometimes our ribcage, against an external force. That's the function I'll focus on in this article.
About the spine
The spine is made up of four main sections: cervical (7 vertebrae); thoracic (12 vertebrae); lumbar (5 vertebrae); sacrum (5 fused vertebrae); and the coccyx.
In rare circumstances people are born with more or fewer vertebrae, and occasionally vertebrae are fused, either naturally or from surgery.
Below you can see a standard spine from the front (left), side (middle), and back (right).
The technical terms for these curves are lordosis and kyphosis, so that’s what you see in the labels on the graphic.
Of course we know the spine can move. It can bend forward and back (flexion/extension), side to side (lateral flexion), it can twist/rotate, and it can do combinations of these. None of those options are as stable as the neutral position though.
You can think of every vertebrae disc pairing as a joint, and each of these joints have a different capacity for movement. In a healthy mobile spine the cervical and thoracic spine have the most movement, and the lumbar spine the least (1). We want to honour that when we move.
The most effective ‘natural’ way researchers have found to cause herniated discs in the laboratory is repeated bending (flexion/extension) of the spine, flexion is what you're doing during a crunch, sit-up, and many other popular abdominal exercises (1).
Another great way to injure the spine is to twist/rotate it under load (1). You may have your own experience of this.
Now you will hear people argue that a spine in a laboratory, doesn't fully represent what goes on in a living human who can heal and adapt (2). They may even raise the fact that the spines in question were mostly pig spines, and pig spines aren't identical to human ones. Finally, some will say that they've been doing crunches, leg raises, or whatever, for years and have no back pain, or that they have even resolved their back pain doing these activities.
Rather than argue each point, I’m going to accept that each of these claims have some validity. It becomes a case of managing risk by picking the safest exercises that fit your context.
What is likely is that some flexion is beneficial because it gets nutrients moving too and around the intervertebral discs (2). That can be achieved by gentle, controlled, and unloaded (no external weight/resistance) movement.
Another thing that I want to make clear is that joints should be moved through a comfortable range of motion frequently to keep them healthy.
The back is no exception, it needs to be moved at each vertebrae, just not under a heavy load in a highly repetitive way. You can find options for mobilising the thoracic spine here for example. After all, you want stability when needed not stiffness all the time.
Endurance vs. Strength
You might assume having great strength in the muscles that stabilise the spine is the answer to avoiding injury. However, the evidence suggests that endurance is key to protecting the spine from injury(1).
This makes sense – if you’re in the middle of lifting something, you don’t want the muscles keeping your spine stable to suddenly give out part way through.
So how do you more safely train your core?
The answer is to mostly train the core for the purpose it was primarily built – stabilisation. Not only is a stabilised spine and more protected spine, but stability through the torso is needed for efficient movement.
In exercise terms, that means anti-flexion, and anti-rotation exercises done with a neutral spine.
The common plank and side-plank are great examples when done correctly, meaning the spine is kept locked in neutral.
The idea is not so much to do these for a long time, but really make them as hard as you can by bracing your core hard and imagining you are trying to fold the ground underneath you. Hold for 10 seconds, rest for a moment and repeat. This prevents extended restriction of blood flow to the area.
The good old press-up, being basically a plank, is actually a very good core exercise if the spine is locked into neutral position and the shoulder blades are kept tight to the rib cage.
Other examples are dead bugs (anti-flexion/extension), Pallof press variations (anti-rotation), and leg tucks (anti-flexion/extension).
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The point is not to use the most resistance or highest repetitions, but to execute the movement pristinely. Record yourself to see if you're hitting the mark. Doing the recordings above was certainly instructional for me.
The myth of spot reduction
No general article on core training would be complete without calling out the idea that doing endless crunches or other ‘abdominal’ exercise will get you a six pack. It won’t.
Now don't get me wrong, exercise can certainly help to get rid of body fat, and the fat within organs (ectopic fat), and fat around the internal organs (visceral fat) may be first on the menu (3-5).
There is even a little research showing that exercising muscle is going to get more fat from nearby than distant fat stores (6), but unfortunately that doesn’t mean training your core is going to result in a flat stomach.
Think about it this way, 1 kg (2.2 lbs) of fat is roughly 9000 kcal. That's a lot of abdominal work. You're better off focusing on exercises that use more muscle mass and therefore burn more energy, and looking at how much and what you're eating.
Diligently train your 'core' to protect your spine, and adopt the mantra that abs are built in the kitchen.
Want to do more than scratch the surface of safe and effective core training?
If you live in the Auckland area, join us for one of our Protect your Spine: Safer and more Effective Ways to Move and Exercise workshops with Dr Christian Thoma (me) to learn more and get hands-on guidance.
1. McGill, S. Low Back Disorders. (Human Kinetics, 2007).
2. Contreras, B. & Schoenfeld, B. To crunch or not to crunch: An evidence-based examination of spinal flexion exercises, their potential risks, and their applicability to program design. Strength & Conditioning Journal (2011).
3. Johnson, N. A. et al. Aerobic exercise training reduces hepatic and visceral lipids in obese individuals without weight loss. Hepatology 50, 1105–1112 (2009).
4. Hallsworth, K. et al. Resistance exercise reduces liver fat and its mediators in non-alcoholic fatty liver disease independent of weight loss. Gut 60, 1278–1283 (2011).
5. Janiszewski, P. M. & Ross, R. The utility of physical activity in the management of global cardiometabolic risk. Obesity 17 Suppl 3, S3–S14 (2009).
6. Stallknecht, B., Dela, F. & Helge, J. W. Are blood flow and lipolysis in subcutaneous adipose tissue influenced by contractions in adjacent muscles in humans? AJP: Endocrinology and Metabolism 292, E394–E399 (2006).