About a year and a half ago I had increasing abdominal tension that turned out to be a ruptured appendix. Emergency surgery that day, a week later an abcess and sepsis, followed by another procedure and hospitalization happened.
What I learned about my core during the months that followed was that even though I was active I was limited. Pushing myself would increase tension and abdominal pain. Core ultrasound showed that not only was my core not contracting during normal actions such as raising my arms or lifting a weight, but I could not engage my core on purpose. With Targeted Core Training i was able to learn how to engage my core through seeing it contract in real time.
There is no better way to check your core and train your core than with diagnostic ultrasound.