"Core training"

Core, trunk, midsection’ strength is necessary for using the full potential and reducing the risk of injury in sports but it is also key factor in health and fitness of general population. Development of the strong ‘core’ should be part of any strength and conditioning routine and fitness program.
There is many variations of abdominal exercise and also many mechanics how the strength in the ‘core’ can be trained. (Check the link for more info about different ideas on the core mecand training: http://breakingmuscle.com/mobility-recovery/how-are-we-still-getting-it-wrongabdominal-hollowing-vs-bracing)

Think of the ‘midsection’ being the chain link connecting upper and lower body. If the link is weak it can get broken once the force is going throughout this link to the distal parts of the chain.

In reality we hardly break our back. However weak link can cause inefficiency and lack of stability for movement which can lead to bad performance and injury. This is happening even in so elementary movement like walking.

Core is the same as other groups of the muscles and it is trainable through the approach of consistency, variability and progressive loading. As with other exercises you start with comfortable intensity and then gradually(linearly or non linearly) adding the load. And also making little adjustments to the exercise.

There is few basic progressions I believe are very effective in developing strong core:

Stability-Ball Rollouts/stir the pot
Trx roll outs
Body saw trx