The science of core training, Part 1

Author doing a push up/hip flexion on ball with hands on medicine ball. This is an advanced exercise that challenges the core muscles as well as the stabilizer muscles around the shoulder joint complex.
Author doing a push up/hip flexion on ball with hands on medicine ball. This is an advanced exercise that challenges the core muscles as well as the stabilizer muscles around the shoulder joint complex.

Core training explained

In years past, athletic trainers rarely focused on training the muscles of the torso, and when they did, they focused predominantly the Rectus Abdominus muscle. In so doing, most of the exercises involved some form of sit up or crunch. This was, however, incomplete training of the core. There are more muscles involved in the strength and stabilization of the core that are far more important than the Rectus Abdominus that needs to be addressed. If not, then the lower back is more prone to injury and the body cannot perform up to it's athletic (or everyday life) capacity. Core training involves exercising the many muscles of the core (the mid section of the body), both in a functional sense and in a stabilizing sense as well. In part one I will explain the muscles of the core that needs to be trained, a brief explanation of the planes of motion, and the types of muscular contractions to utilize. In part two I will give some exercise examples and practical applications.

The muscles of the core

The muscles of the core mean different things to different fitness consultants. Pilattes instructors look at the muscles of the mid section, along with the muscles of the pelvis as making up the core. Other trainers consider the muscles making up the abdominal wall as the core. I consider the core muscles to include the lower back as well as the abdominal muscles, but I do not consider the muscles of the pelvis to make up the core. They are in a different area, and require a different focus. For the sake of keeping this article a little shorter, I will not go into detail of the lower back muscles, just realize that they contract with the ab muscles to give stability to the spine, and also to create movement. In ths article I want to focus on the abdominal muscles.

The Rectus Abdominus

The Rectus Abdominus is the most popular of all the core muscles. It attaches via tendons to the breast bone and the pelvic girdle. When the Rectus Abdominus contracts, it brings the chest and pelvic girdle closer together. A good example is the crunch. The Rectus Abdominus is the muscle that has the six-pack look when it is strengthened and an individual has low body fat levels. Conventional wisdom says that one must do hundreds of crunches a day to get that look. It is not true. The truth is, if you do too many crunches to the exclusion of the working the other core muscles, you would actually train the nervous system to recruit the Rectus Abdominus first when you need to stabilize the core for anything you do (lifting a box off the floor, doing a barbell squat, etc..). This is the law of facilitation. The Rectus Abdominus should be the last muscle of the core to engage for stabilization. It is good to train the Rectus Abdominus, but use more intensity, less total sets, and spend more time training the other core muscles.

The Oblique muscles

There are two types of Oblique muscles, the internal and external Obliques. The fibers run at a diagonal pattern from ribs to the linea alba (the fascial tissue) of the Rectus Abdominusand pelvis. When they contract, their primary motion is torso rotation, and they also assist the Rectus Abdominus to bring the upper body closer to the pelvis (crunch).

The Transverse Abdominus

The Transverse Abdominus is the deep muscle of the core. It is attached to the Linea Alba of the Rectus Abdominus (the fascial tissue that runs up and down in the center of the Rectus Abdominus, separating it into right and left halves), and runs horizontally around to the back and attaches to the fascial tissue that surrounds the spine. A good visual would be to imagine it as girdle that sits beneath the Rectus Abdominus and Oblique muscles. In my opinion, this is the most important muscle for core stabilization and spinal protection. When engaged, it literally decompresses the spine when under load. For example, while doing a barbell squat, the compressive forces of the barbell going through the body is counterbalanced by the decompressing capability of the Transverse Abdominus, thus giving the spine support and protection. This goes for any kind of lift, be it lifting a box off the floor to doing arm curls and anything in between. The Transverse Abdominus must be engaged. How do you do it? Whenever you get ready to do any lift, square your shoulders back, get into a neutral spine (maintain a slight curve in your lower back, like you would stand normally), and suck in your belly button about 1/4 of an inch, and maintain that throughout the lift. That's it. The Transverse Abdominus is "on". I want to point out a couple of interesting facts about the Transverse Abdominus. First, it is not a muscle that gets bigger or stronger with training. It is just either "on" or "off". If it is "off", your lower back is very exposed to outside forces that can lead to injury. Second, turning "on" your Transverse Abdominus should be an automatic, intrinsic response to prepare for a lift, however, because we as a population have become more sedentary, that intrinsic response has been shut down. Another factor that leads to the Transverse Abdominus not working is that fact that many people do many reps and sets of crunches, reprogramming the neural response to engage the Rectus Abdominus to be the first muscle recruited for core stabilization (the law of facilitation in effect again). The Rectus Abdominus is the superficial muscle too far away from the center of the core to do an adequate job of stabilization and protection. In other words, you must make a concentrated effort to turn on your Transverse Abdominus for your lifts, and practice to make it an intrinsic response.

The planes of motion

When exercising, one must also consider the planes of motion and how they interact with strengthening and stabilization. There are three planes of motion that the body moves in (that is where we get 3D). The first one is the Sagital plane. Imagine a wall that goes down the center of the body splitting it into left and right halves. That wall would describe the Sagital plane, so if you create movement in the Sagital plane, it would be a forward or backward movement. An example would be a crunch or backward bend. It also applies to body parts, such as doing a bicep curl. The second one is the Frontal plane. This would divide the body into front and back halves. An example of movement in the Frontal plane would be raising your arm up to the side. The final plane is the Transverse plane. This divides the body into upper and lower halves, and movement in this plane would be something like a torso twist. So what does this have to do with core training? The three planes apply not only to motion, but to what direction the load , or external force is coming from. For example, if you hold a weight in your hand while it is extended to the side, that load transfers through the arm and through the body from the frontal plane, that the core and other muscles must stabilize against to maintain form. This is just one example of how you can work the core, even without movement in the mid section of your body. Understanding the three planes of motion adds a lot of variety to how you can train the core, and thinking of exercises besides the crunch or other conventional exercises. One other point: it better trains the body in a more dynamic, functional sense that translates to a body you can count on in demanding situations outside the gym.

Types of muscular contractions

The final thing to consider for absolute core conditioning is the types of muscular contractions that occur and how to use them. There are three kinds: concentric, eccentric, and isometric. Concentric muscular contractions shorten the muscle. Eccentric contractions lengthen the muscle under load, and isometric means no change in length but still working under load. An example of  the concentric phase of movement is when during a bicep curl, one is raising the weight, shortening the bicep muscle to do it. The eccentric portion is when one is lowering the weight in the bicep curl, lengthening the bicep (remember, the bicep is still under load because of where the load is coming from. Many people assume that the triceps are working at this point, when they are not). An isometric contraction would be holding the weight mid-point without movement for a period of time while holding the weight. Understanding the types of muscular contraction, one can design an unending array of exercises designed to work the core, even without crunching or twisting (these movements do work, and should be used). For example, I have clients do what is called a supine airplane. They would lie down with their head and shoulders on the ball, face up. Once in this position, I have the client come off to the side so that one shoulder is on the ball and the other shoulder is not while not allowing the shoulder off the ball to drop. Then I will have them hold that for ten or 15 seconds. When they are done I have them do the other side. Since there is no movement, the core has to do a static contraction hold, forcing it to work in a stabilizing sense.


By understanding the muscles of the core, along with the planes of motion and types of muscular contraction, one can design a much more rounded and complete training program for the core. Another point to keep in mind is that most, if not all exercises performed properly do train the core. For example, when doing a bicep curl, if one maintains a neutral spine and does not hoist or swing the weight, the biceps get more overload forcing them to work harder, and the core would be doing a static contraction hold working harder as well. Problems arise when one starts to swing the weight, arching the back, and not maintaining neutral spine. In part two I will describe some rather interesting and unique exercises along with a video demonstration to train the core based on these insights.

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Dan Levesque 21 months ago

This is a great basic article. Nice job!

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