Muscles around your midsection, including the lower back, must be strong

A lot of people would benefit from a better understanding of the concept of the body's 'core.' Many exercisers consider 'core' to be another word for the abdominal, or stomach, muscles. Although these muscles are involved, trained practitioners in the industry actually use 'core' to refer to a comprehensive body system rather
than a specific group or groups of muscles. This system includes muscles, connective tissue, skeletal structures, breathing patterns, neurological activation, movement strategies and sequences, and more.

Rob Williams