Some common symptoms of people who suffer from poor "core stability" include:

• Recurrent, niggling injuries. Especially on the same side of the body
• Recurrent low back pain
• Pains that appear to come out of nowhere or after doing very little
• Tightness and pain through the neck and upper back with prolonged sitting. Eg working long hours at a computer
• Injuries that appear with an increased training load
• Incontinence (poor bladder control)

If you are one of these people, it may be worth getting it checked out by a physiotherapist.