The Principle of Specificity is that you should train the way you want your body to adapt and improve its function. Most human movements require coordinated action of many joints and muscles.

Hitting a forehand in tennis, for example, involves initiating the movement with the legs and transferring force across the midsection to the upper body.

The force transfer depends on a stable spine provided by the muscles of the “core� – 29 pair of muscles that support the spine, hip and pelvis.

Mark Faries and Mike Greenwood from Baylor University cleared up misconceptions about core training. The core muscles must have good endurance to provide stability and strength to promote movement.

Most books and articles on core training emphasize static postures, such as side-bridges, planks, back-bridges and various postures on exercise balls but neglect dynamic exercises that require a stable spine. While static exercises stabilize the spine, they do not fully prepare the body for force transfer between the lower and upper body.

In other words, they are not specific. For example, simulated wood chopping on a pulley machine develops strength, power and spinal stability that would be valuable when throwing a softball or Frisbee, hitting a gold or tennis ball or throwing a strike in bowling.

Another example is hoisting a dumbbell from the floor to overhead with one arm and in one motion (one-arm dumbbell snatch). This exercise builds large muscle groups throughout the body and requires a stable spine during an extremely dynamic motion.

Core training is important for pain-free back and dynamic strength and power that will improve the way you move. Make your training functional and build the core muscles statically and dynamically. [sources: Strength and Conditioning Journal, Fitness RX]