What is the core? I like to break it down into basically everything from your rib cage to mid thigh. We often think of the abdominal muscles, some of us remember our back muscles. But few think of the pelvic floor, our glutes, hip flexors, and even the diaphragm.
Yes these are all core - lets break it down into function so it makes strengthening each muscle easier.
Abdominals - these stabilize the low back and hold in the tummy. These are the rectus abdominis (6-pack muscles), obliques (the sexy V muscle some people have) and transverse abdominis (deep to the other 2 and what I believe to be the biggest pain reliever and function improver for those with back, hip, knee and even ankle pain. These also perform forward flexion - think of your traditional sit up. Though sit ups are not my favorite way to strengthen these!
Low back muscles. These include lots of fancy muscles but basically perform trunk extension - think of the superman exercise when you lay on your stomach and lift your arms and your legs off the ground. There are also muscles that facilitate side bending call quadratus lumborum (named after their square shape and location in the lumbar spine).
Pelvic floor. One of my favorite and commonly neglected by health care providers! These muscles assist in sexual function, control of bowel and bladder, literally hold your guts up from falling to the floor when standing, and STABILIZE the core. Very important with breath, strengthening and everyday tasks. Like I said, under educated.
Hip flexors and glutes; the front and back of the hip. Essential for gait, running, horseback riding, skiing, getting dressed and so much more! Most commonly people are strong and or tight in the in hip flexors (mainly due to extended hours sitting) and we neglect the glutes. Check out my Spring Series video for a great way to strengthen the lateral hip! https://youtu.be/sCbvKzTkweo