There’s much debate about core strengthening: which exercises are best, how much training volume is ideal, which muscles to target, etc. The list goes on and on, and there's no shortage of people who claim to have the secrets to the ultimate core. While I certainly don't claim to have all the answers, I do want to share my fundamental beliefs on HOW the core should be trained. My hope is that the reader is left with a better understanding of the WHY behind training the core. It should be noted that 99.9% of the content in this article is not original. It's my (hopefully accurate) interpretation of the works of Dr. Stuart McGill PhD and Dr. Shirley Sahrmann PhD. If you don't know who these people are and you're fascinated with biomechanics and the human movement system, you should look them up.
Optimal Back Health
It seems the 2 best attributes of a resilient back are muscular endurance and neuromuscular control.
1) Muscular Endurance
Most of us think about getting stronger because, intuitively, it sounds like a good thing. But when it comes to the spine, is this the case? Not according to Dr. McGill. Apparently what is more important is muscular endurance, i.e. the ability of a muscle to perform submaximal contractions for an extended period of time. While having muscular strength can improve your body's muscular endurance capacity to some extent, it's more important to train the muscles that stabilize your spine for muscular endurance instead of muscular strength. Think about this concept in terms of your daily life. The muscles of your spine are constantly working throughout the day. Yes, even when you're sitting. Low level, long duration muscle contractions are most important for the vast majority of us.
2) Neuromuscular Control
Another aspect of spine health comes in the form of neuromuscular control. Simply put, this is your body's ability to coordinate precise movement to achieve a goal. The human body is overloaded with redundancy, meaning that we can perform a variety of tasks in many, many different ways. This can be a great thing for many reasons, but it can also be problematic if we learn pathologic movement patterns. A common question I receive when I tell people that the way they are moving is causing them pain is, "Why would I move this way if it's making me worse?". I believe the answer is that your body doesn't have the best concept of what ideal biomechanics are, nor does it particularly care. What IS important to your brain is accomplishing tasks quickly and efficiently. In other words, instead of asking, "What's the best way to perform this motion?", your brain asks, "What's the fastest and most energy efficient way to perform this motion?". This is a great thing! It saves a tremendous amount of time because your brain simply retrieves a stored motor program from the motor cortex of your brain, versus considering how the task is performed. For example, to get from point A to point B, your brain thinks, "walk" instead of "Shift weight to the left, flex the right hip, extend the right knee..." etc. But again, it does so at the expense of potentially harming your body.
Functional Purpose of the Spine
It’s my belief that the purpose of the spine is to serve as a rigid structure to transmit forces between the upper and lower extremities. There should be as little motion as possible through the spine when performing weight-bearing activities, as accessory motion bleeds force transmission. The spine is surrounded by ball and socket joints at the shoulders and the hips, which are conducive to motion. Additionally, the components of the spine apparently don't tolerate (i.e. their integrity is compromised faster over time) lots of motion well, especially when an external load is applied to it. Because the joints of the spine inherently provide less motion than the joints of the shoulder and hip, it is advantageous to train your body accordingly- strengthen the muscles of the spine to stabilize, strengthen the muscles of the shoulders and hips to generate power.
Brief Overview of the Intervertebral Disc
It’s important to realize that the intervertebral discs of the spine are very different than other structures in the body. Their design dictates that, unlike other structures (muscle, for example), their strength does not increase with progressive overload. This is important. Stressing the disc maximally is accomplished by flexing the lumbar spine to compress the disc, as would be performed during a crunch or sit-up, and then rotating the spine (see video below). Your genetics, posture, and daily movements allot you a certain amount of spinal flexion cycles throughout your life. This number cannot be increased for the most part, at least as far as research currently suggests, but it can definitely be decreased. The best way to decrease your given number of flexion cycles, a.k.a. herniate a disc, is to perform loaded spinal flexion while adding a twisting motion. In other words, don't do this:
The disc is pushed posterior with spinal flexion. This is normal and not typically problematic, but it can be if you have a herniated disc and/or symptoms of nerve compression. Furthermore, holding gentle spinal extension postures can push the contents of the disc back to where they belong, taking stress off of the spinal nerve root and providing pain relief. However, please note that excessive spinal extension places increased stress on the facet joints of the vertebrae, which can be painful as well. Which reiterates my point that it’s important to strengthen the spine in a neutral range of motion!
Training the Core as a Rigid Unit
To do so, you must perform isometric contractions of the abdominal and back musculature. For those that aren’t familiar, there are 3 basic types of muscle contractions- concentric, isometric, and eccentric (see below). We want to perform isometric contractions of the abdominal muscles because during these contractions, the muscles stay the same length and provide stability to the spine. So instead of doing sit-ups, back extension, and other exercises that emphasize spinal flexion and/or extension, try those that demand stability at the spine and motion through the hips and shoulders. Skip to the end of this article if you're desperate to see a few examples.
Concept of Passive Muscle Tension
This is an important concept to understand. The idea is this: the more dense your muscle fibers are, the more resistant to motion they become. Surely you've seen the guy at the gym that's so big he can't scratch his back. He traded mobility for stability a long time ago! While this situation is probably a bad thing, or let's just say less than ideal, it's a fantastic problem to have when it comes to the spine. So, the stronger you make your abdominal and back muscles, the more stability (resistance to motion) they will provide- even when you’re relaxed! This is why performing a consistent core strength/endurance program is important, although it admittedly does take time to develop the necessary increased size in muscle fiber diameter to provide more stability. Search "muscle fiber titin" if you're more interested in how this works.
Role of the Transverse Abdomens (TrA)
In my world there's a lot of discussion regarding this muscle and it's importance. It is my opinion that there is benefit to training the TrA, but it's primary benefit is in the neuromuscular department and not the muscular strength/endurance department. The initial fascination with this muscle stems from a research study that showed there was delayed activation of this muscle in patients with low back pain. Interesting, yes. But does improving the strength of this muscle translate to improved spinal stabilization and, perhaps more importantly, decreased back pain? Sometimes, but possibly not as effectively as if you were to train the abdominals as a whole. The reason for this is that if you over-contract the TrA and shorten the muscle, you actually decrease the mechanical advantage of the other abdominal muscles (see below).
This is important, because these other muscles provide more stabilization to the spine than the TrA. For example, during a 1 rep maximum deadlift attempt (when a weightlifter tries to lift the heaviest load possible) where the body seeks the utmost spinal stability, you do not see the abdomen maximally drawn in, which would indicate maximal shortening of the TrA (letter "c" below). Instead, you see a relatively neutral abdomen (letter "a" below) that is maximally contracted. This is because this provides the ideal length-tension relationship for the abdominal muscles to contract and produce a spinal stabilizing force. Conversely, if the weight is too great and your abdominal muscles fail to stabilize your spine, you may see the abdomen begin to enlarge (letter b below) as the abdominal muscles begin to elongate. This is why weight belts come in handy when lifting maximal loads.
I’m a fan of Stuart McGill and his Big 3 for the core. These exercises are designed to promote strength in muscles stabilizing the back in an isometric manner, while sparing the discs and joints of the spine.
For the sake of keeping this article relatively short, I'm not going to elaborate on these exercises, but I will offer this video of Dr. McGill covering them, along with a few modifications (below). Additionally, you may now better understand why exercises like squatting, deadlifting, push-ups and pull-ups are ideal for developing core strength- they each maintain a neutral spine while facilitating power development through the hips and shoulders- when done properly.
I'll also provide the obligatory warning that if you already have back pain, there's a chance these exercises could make you worse if you don't understand your individual pain triggers. Furthermore, there's a chance you don't have back pain, and these exercises aggravate your back. So, proceed with caution, and if you have any concern, please check with your physical therapist first before engaging in these exercises!
Develop muscular strength and endurance by mastering these isometric exercises. Perform these exercises consistently and progress them appropriately to improve your neuromuscular control of your spine. Stop doing high repetition spinal flexion and extension exercises. By training your core isometrically, you will add years to your back and improve your quality of life. And maybe, you’ll start to notice your abs again!
Dr. William Richardson is a board member and program director for Work Out Help Out. As a certified personal trainer and licensed physical therapist, William has extensive knowledge about the human movement system and is passionate about joining exercise and volunteer service to change the health of the nation.