The muscles we refer to when we say core muscles are the muscles of the torso and spine.
The major core muscles are as follows:
1. RECTUS ABDOMINIS – A big player in core strength and stability, this paired muscle runs on either side of the spinal column and is the stuff six packs are made of. Washboard abs get their definition from bands of connective tissue running across the muscles, there’s no pack of 6 or 8 muscles tucked away in there. To speak of lower abs and upper abs makes no sense! The two rectus abdominis muscles work when the spine flexes. (Find out more at Four Facts about Six Pack Abs).
Fitness Trivia Question: What is the name of the long band of connective tissue separating the paired rectus abdominis muslces? Answer is below.
2. EXTERNAL AND INTERNAL OBLIQUES– Oblique muscles fibers are diagonal muscle fibers. The external oblique muscle fibers (simply external obliques) run in the opposite direction of the internal obliques. The internal obliques, as you might have guessed, lay deep beneath the superficial external obliques. Both the internal and external obliques are best strengthened with core exercises that involve a diagonal movement.
Obliques for Lateral Flexion? Most kinesiology textbooks state that the obliques only assist with spinal lateral flexion, they are not prime movers. The obliques are prime movers for spinal flexion with rotation.
3. TRANSVERSE ABDOMINIS – The deepest abdominal muscle is responsible for abdominal compression (think stomach tightening to take a blow), as well as vigorous exhalation and expulsion (i.e. heavy breathing in and out). When your group fitness instructor tells you to “pull your belly button in to your spine” or “draw in your abs”, you’re squeezing your transverse abdominis muscles. Tightening the core during physical exertion is paramount for injury prevention and spinal health.
Trainer Tip: Whether you’re an instructor or a personal trainer, you must cue your clients on posture that supports the spine. Reminders to keep the abs tight and the spine in a neutral position should have you sounding like a broken record.
MUSCLES OF THE SPINE
1. QUADTRATUS LUMBORUM– This very deep, vertical muscle essentially connects the lowest ribs to the pelvis on each side. It’s the primary mover for spinal lateral flexion, not the obliques! (Remember that for your CPT exam ;))
2. ERECTOR SPINAE – If you’re wondering what muscles provide the strength and flexibility to get you in a back bend, look no further.
The prime mover for spinal flexion is the erector spinae, opposed by the rectus abdominis. The large, flat superficial erector spinae actually consist of three pairs of muscles: the iliocostalis, longissimus and spinalis. Back extension exercises will eventually leave your low back muscles bulging like the muscle head on the right.
3. MULTIFIDUS – another super deep muscle, this one is located under the erector spinae and is an important spine stabilizer as it connects vertebrae together! The multifidus is a prime mover for all the same joint actions as the erector spinae – spinal extension, rotation and lateral flexion. The only spinal muscle you can noticeably tone is the erector spinae. The multifidus and quadratus lumborum are too deep to showcase their strength with a muscle flex. There are other back muscles, of course, but they are not involved in the movement of the spine.
Fitness Trivia Answer: The long, flat rectus abdominis muslces run on either side of the linea alba, Latin for “white line”. This band of fibrous connective tissue runs down the midline of the abdomen in humans and other vertebrates.