The core is normally thought to be having a 6 pack but thats just scratching the surface and is more to do with your Body Fat % than having a strong core. Everyone has a six pack (you might not be able to see it but its still there) most people have a weak or under utilised core. The core is essential for protecting the spine during movement, developing quality of movement, breathing, injury prevention and athletic development.
So what muscles make up the "core"?
The major muscles included are the pelvic floor muscles, transversus abdominis, multifidus, internal and external obliques, rectus abdominis, erector spinae (sacrospinalis) especially the longissimus thoracis, and the diaphragm.
What do these muscles primarily do?
Protection and stability of the spine while the extremities move, pelvic tilt (anterior/posterior/laterally/rotational), flexion (anterior/posterior/lateral) & rotation of the trunck (body) and breath control.
Why are these functions so important in every day living and performance?
It is super important to realise the importance of anti-rotation, anti-flexion and anti-extension and the role in your daily movements to protect and stabilise the spine. Having the "core" strength to resist movement and bring your hips back under your body while you move your extremities is vital in reducing the chance of chronic pain and injury.
At a performance level it is even more vital in force production and injury prevention. A strong core allows you to maintain ideal hip positioning and develop force correctly. Watch Usain Bolt sprint at the Olympics and you will notice strong and engaged core muscles that lock the hip and allow him to maximise force production into the floor. This applies for all land based sports that require you to run, sprint and change direction . The same concept applies to swimming, being able to lock your hips into the correct position to stop them from "wiggling" around while swimming greatly reduces drag and increases power development.
How should we develop a strong "core"?
The most effective way that has the greatest transferability to life and sport is anti-movement core exercises such as, Plank variations, Farmer carry variations, anti rotation variations and diaphragmatic breathing exercises. These exercises will develop more muscles at once than your generic sit ups and crunches and will transfer across to the real world.