Core Training Basics
- Ben
- May 30, 2018
- 8 min read
As a kid in gym class, crunches and sit ups were always the only ab/core exercises I remember doing on a regular basis. Occasionally we would do things like planks and side planks, but the majority of the core work that was done included large amounts of spinal flexion and extension. While these types of exercises certainly deliver a good “pump”, they don’t really work the core in the way that it is meant to function. Now there may be a time and a place to include some crunches and more dynamic core exercises, but for most people they are unnecessary and possibly harmful to your back. Sure you will strengthen your abs and probably eventually get a nice looking mid-section (a lot of that will depend on your diet) but you can get the same results training your core in a more functional and safe manor. Before getting too far into the fundamentals of good core training, let’s take a brief look at the anatomy of the core and how it was designed to function.
When looking at the anatomy of the core, you can start to understand how it is designed to work and its role in human movement. First it is important to define what “the core” actually is because most people conflate the core with the rectus abdominis muscle or the “6 pack”. The core can be defined as the majority of the axial skeleton from the pelvis to the shoulders. The core musculature is set up to stabilize the lumbar spine and transfer power and force from the lower extremity to the upper extremity. The axial skeleton is composed of four segments: the pelvis and sacrum, cervical spine (neck), thoracic spine (upper back), and lumbar spine (lower back). The purpose of each segment of the spine is different. The pelvis and sacrum can be thought of as an extension of the lumbar spine and its role and function are integrally linked with the lumbar spine. The pelvis connects the axial skeleton to the hips and lower extremity. A stable pelvis and lumbar spine are vital for allowing the hips to realize their full mobility and range of motion. The lumbar spine is a stable segment of the spine and is not meant to move much. Each individual vertebrae of the lumbar spine can only rotate ~2-5° and the entire segment of the lumbar spine can only rotate a total of about 13°. Now the thoracic spine’s role is much different than the lumbar spine and it is a much more mobile segment. The thoracic spine is designed to rotate, flex and extend with much more freedom than the lumbar spine. It also does not support as much weight as the lumbar spine so the compression and shear forces are less on the thoracic spine. You may begin to notice that the role of each joint of the body seems to alternate from a mobile joint to a stable joint (the hips are a mobile joint, the pelvis/lumbar spine is stable, the thoracic spine is mobile and so on). The entire body actually functions in this way and Mike Boyle and Gray Cook has coined this as the joint by joint theory. I am not going to go into more detail about the joint by joint theory here, but you can read more on it here: http://www.strengthcoach.com/public/1282.cfm. Or check out these videos by Stuart McGill and Kelly Starrett which explain the same concept in a different way:
So now that we have looked at the bony anatomy of the core we can start to understand how the musculature is designed to work. There are 4 main muscles that make up the core musculature (there are a lot of small stabilizing muscles around the spine too, but we are going to ignore those for the sake of simplicity). The four main muscles are the rectus abdominis, external obliques, internal obliques, and transversus abdominis. The rectus abdominis is the most recognizable of the 4 muscles and it is what creates the 6 pack look. The muscle attaches the front of the pelvis to the bottom of the sternum and is responsible for flexing the rib cage. Start to think of the action of the rectus abdominis not so much as spinal flexion but as posterior pelvic tilt (the tilting of the pelvis backward) and internal rotation of the rib cage (the pulling of the rib cage downward). The rectus abdominis really is a big player in keeping our pelvis and lumbar spine in a neutral position through posterior pelvic tilt. Most people can recognize the external obliques as the muscles that run on either side of the rectus abdominis. The internal obliques run deep to the external obliques in the opposite direction. If you were to put your hands on your waist with your fingers pointing toward the middle of your pelvis, that is the direction of the fibers of the external obliques. The internal obliques run perpendicular to that. The obliques are also important in controlling pelvic tilt, but they also rotate/ resist rotation and laterally flex/ resist lateral flexion of the lumbar spine. Lastly, the transversus abdominis is the deepest of the 4 muscles and raps around the entire midsection from the lumbar spine to the linea alba (the mid-line of the rectus abdominis). You can think of the transversus abdominis as nature’s weight belt. Its main job is to compress the abdominal cavity to create pressure in the abdomen. This pressure is what protects the spine under load. Now that we have a solid understanding of the basic anatomy of the core, let’s look at the function and how to train the core optimally.
As mentioned earlier, the lumbar spine is not designed to move much. Each individual vertebra can only rotate a couple of degrees. Think of the lumbar spine as the foundation of a house. Without a stable foundation the house will collapse. So now you might be asking what does this have to do with core training? The answer is that we should be training the core to be good at what it was designed to do. This means that the exercise selection we use for training the core should center on exercises that teach us to maintain a braced, neutral and stable core under forces from many different directions. In other words, we should train the core to resist motion. We can break core exercises into a couple different categories based on the direction of force we are resisting. The spine can move in all three planes of motion (sagittal, frontal and transverse). This allows the spine to flex, extend, laterally flex and rotate. It is important to be able to keep the spine stable in all three planes of motion. The terms that are used to describe this are anti-extension, anti-flexion, anti-rotation and anti-lateral flexion. The majority of training should be centered on anti-extension and anti-rotation exercises as these are typically the biggest areas of weakness. Furthermore, anti-flexion and anti-lateral flexion strength can be gained through upper body pulling exercises and exercises that challenge our ability to maintain upright posture like deadlifts and weighted carries.
Understanding how the core operates in everyday life gives a clearer picture of why dynamic exercises like crunches and sit ups are not as beneficial for core strength from a functional stand point. The fact of the matter is that the exercises that take the spine through a large range of motion, while being useful for things like hypertrophy and general strength, may in fact increase your risk for back injury. Repetitively taking the spine through flexion and extension has been shown in the lab to lead to disc injuries (1,2). Additionally, it has been demonstrated that crunches place as much as 2,000 N of compressive force on the spine (1). Putting that much compressive force on the spine is probably not a great idea, especially when there are more effective means to strengthening the core. There is an argument to be made that the compressive forces documented in research and the way in which researchers were able to demonstrate the damage that can be dealt to the vertebral discs through repetitive spinal flexion under load in the lab aren’t entirely applicable (3). This being because much of the research has been conducted using animal spines; specifically the cervical spine which has many differences in structure as compared to a human lumbar spine (3). However, regardless of if you are or aren’t doing a significant amount of damage to you spine through dynamic core exercises, you are still failing to train the core in how it is designed to function. Very rarely do we ever take the spine through the ranges of motion of a crunch or sit up and it is never a good idea to do so under load.
As mentioned earlier, the spine can move in all three planes of motion and it is important to have stability through all three planes. This means a complete training program should consist of core training that utilizes anti-extension, anti-rotation and anti-lateral flexion (as mentioned before, anti-flexion is trained through exercises like deadlifts, RDLs and upper body pulling). A good place to start is with what Stuart McGill has named the “big 3” of core exercises.
I think McGill’s “big 3” gives a good jumping off point for understanding anti-extensio. Anti-extension exercises can generally be broken up into supine (on your back), prone (on your stomach) and overhead exercises. McGill hits on two of these with his “big 3”. Supine exercises would include things like McGill’s curl up and deadbug variations; whereas prone exercises would include things like plank variations and ab rollout variations. To add to that, any overhead exercise where you have to take the shoulders near end range flexion is going to be a significant anti-extension challenge. The one thing that McGill’s “big 3” does neglect is anti-rotation exercises. This is where exercises like pallof presses and cable chops and lifts come into play. There are countless variations with all of these exercises that can be used as progressions and regressions and there is plenty of room for creativity. As long as you make sure you include exercises that challenge core stability in all three planes of motion, the sky is the limit as to what exercises you choose to include in your program.
Pallof Press:
Cable Chops and Lifts:
The importance of a strong and stable core is undeniable, but there is often confusion over what effective core training looks like. The purpose of the core musculature is to keep the spine in stable and safe positions while under load, so we should train it to be really good at that. Everyone, from Lebron James to your grandma, needs to have core stability in all three planes of motion and we can train these qualities with proper exercise selection. Avoid the dynamic core exercises that take the spine through large ranges of motion and swap those for exercises that focus on maintaining a neutral spine while resisting forces from all three planes of motion. The core is a very interesting and complex muscular system and it has so much more function than just flexing and extending the spine. In future posts I will talk about the core’s function in breathing and how important the breath is in strength training, sport and everyday life.
As always, thank you for taking the time to read this. If you enjoyed this post and think that the information presented is worth someone’s time, please share this. If you have any questions or comments or there is a topic you want to see me cover in a future post, please leave a comment or send me an email at 510strengthconditioning@gmail.com.
References
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 Exercise, 29, 804-811.
2) Callaghan J.P. & McGill, S.M (2001). Intervertebral disc herniation: Studies on a porcine model exposed to highly repetitive flexion/extension motion with compressive force. Clinical Biomechanics, 16, 28-37.
3) Contreras, B. & Schoenfeld B. (2011). To crunch or not to crunch: An evidence-based examination of spinal flexion exercises, their potential risks, and their applicability to program design. Strength and Conditioning Journal, 33(4), 8-18.
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