The plank is an awesome exercise that focuses on strengthening your core and increasing trunk stability.
However, a lot of people tend to over arch in their backs, their necks and let their belly's drop to the floor. This will increase the chances of sustaining a lower back or neck injury.
To get the most out of this exercise it is important to maintain a neutral spine. Here is quick checklist:
1. Head looking down not up - avoid hyperextension of the neck
2. Pelvis tilted backward not forward which allows for a flatter lower back
3. Keep your core tight, trying to pull your pubic bone up to your sternum (chest)
4. Squeeze the glutes and the abs
5. Don't break from this position!
Core stability is essentially how well you can hold this position throughout other movements. Holding a neutral/straight spine in this exercise will transfer and add stability to all your other movements. Whether it's a squat, shoulder press or even a push-up. Holding a neutral spine is vital to avoiding unwanted injuries.
Any questions feel free to drop a comment below :)
Angelo Campanella