For resources on core exercise check these out:
https://www.healthline.com/health/best-core-exercises
https://www.mayoclinic.org/healthy-lifestyle/fitness/multimedia/core-strength/ sls-20076575
For the source and more information about your core, check it out: https://www.health.harvard.edu/blog/understanding-and-improving-core-strength- 2018090414662