Concepts of Core Training
The muscular system of your body works in a synergistic fashion. What this means is that it takes more than one muscle to perform a movement. A bunch of muscles working together are required to perform a certain movement. For example, when you perform a bicep curl you must hold some form of weight firmly with your hand while tucking your elbows into the sides of your body. You then bend your arm, squeezing your bicep muscle, which exerts enough force to bring the weight up and lower it back down.
To perform even a single bicep curl, far more than just your bicep muscles are working to bend and straighten your elbow while maintaining a semi-natural posture. The muscles surrounding the shoulder girdle are required to stabilize your shoulder joint. The muscles in your forearm (and there are a lot of them) work hard to assist the movement of the elbow and maintain the firm grip necessary to keep the weight in your hand.
The next time that you are in the gym doing bicep curls, lateral raises, or any other standing exercise, notice what is happening to the muscles in the trunk of your body. If you make an effort to be observant, you will feel that your core muscles are recruited to stabilize your body, counteracting not only the momentum of your body motion but also the gravitational force of the weight you are moving.
Stabilization is a major component of core training. If you can learn how to get these core muscles to recruit or fire more often with movement and during exercise, you will notice that all of your strength and endurance activities will increase to a higher level of performance. Think of the core of your body as a foundation. Once you have a strong foundation, all of the added parts will have a much better base from which to work.
Although the muscles in your core stabilize your pelvis, shoulder girdle, and spine, they are also required to move these same areas. The core muscles must be strong enough to distribute your body weight, absorb and transfer forces placed upon the body, and generate force to move through your daily activities.
Stabilizing your core muscles also strengthens them — your core stabilizes your body, which allows you to do the exercise. You cannot have one without the other, which goes back to the idea of appropriate progressions. There is a certain amount of stability needed to strengthen, yet there is also a certain amount of strength needed to stabilize. In order to be as mechanically efficient as possible, you have to train for both.