You hear a lot of foul language in the gym. (Admit it - that's one of the reasons you like going.) But there's one four-letter word that should make you cringe whenever it comes up. That word is core. And the reason it's so obscene is because most of the time, people throw the term around carelessly, without knowing what it really means. Think you're in the clear? If you just said, "I know what the core is - it's your abs and lower back," go wash your mouth out with soap. Then come back and finish this article, in which you'll learn about the body's many cores and how to train each of them.
In order to condition your whole body, you need to perform exercises that strengthen the area surrounding the spine - namely, the abs and lower back. Yes, banging out a set of Swiss-ball crunches can be a part of that training, but it's only the tip of the iceberg when it comes to true core conditioning.
CORE CONCEPTS
Stability training has been going on for eons,but its modern incarnation dates back roughly 25 years. Physical therapists in San Francisco discovered that having their patients train in unstable yet controlled positions (such as on a Swiss ball or balancing on one leg) could alleviate back problems. The concept later became part of the "functional fitness" craze of the '90s, in which more sport- and lifestyle-specific training methods began to replace old-school lifting programs. (In other words, people began to see weight training for health and performance as more than just bench presses and biceps curls.)
In both cases, the training focused on knocking the body off balance so that the central nervous system (the organizer of all your body's muscle activity) would be forced to recruit more muscle fibers to complete the task at hand. Which means when you do Swiss-ball crunches, for example, you're not only training your rectus abdominus (the six-pack muscles), you're training your brain to activate all the other muscles that help keep you on that ball - including your internal and external obliques, transverse abdominus, quadratus lumborum (in your lower back), and many other small but important supportive muscles for your spine.
Once the central nervous system has learned to recruit all those additional muscle fibers (ones that wouldn't necessarily be activated during a traditional crunch), it can put them to use in other exercises and activities- not only helping improve your performance on the Swiss-ball crunch but making your abs pop as well. Essentially, this means that training your body to stabilize itself leads to an overall heightened communication between your brain and muscles, which can lead to a greater capability to build muscle and burn fat, faster recovery times, and greater sports skills with a reduced risk for injury.