crossfit core muscles

The core and pelvic floor muscles

A simple way to understand the Core is to simulate it with a cardboard box.

In this box we have a lid that will be the diaphragm, the sides of the box will be the abdominal muscles: in front we have the transverse, internal oblique, external oblique and rectus abdominis; the posterior part will be made up of the psoas, quadratus lumborum, multifidus and spinal erectors.

pelvic floor crossfit

The bottom of the box will be the pelvic floor muscles.

If this cardboard box is filled with books and we do not activate the abdominal and lumbar muscles, when moving these books they will push the side walls breaking / damaging the box.

Visualize muscle activation as the packing tape that we place to reinforce and protect the box from breaking (the muscles from injury) ; in the same way that if we fill the box with books, we put that packing tape only on the sides and lift the box, the bottom part of the box will most likely receive all the pressure and the books will fall (prolapse or weakening of the muscles), so to avoid this we must place the packing tape (activate) also on that bottom cover.

The muscles that are part of the Core


The diaphragm is activated when you inhale. As it descends it expands the rib cage especially the lower ribs redirecting the internal abdominal pressure (IAP) down.

diaphragm core

You can feel this by placing your hands on the lower ribs and inhaling deeply. You will feel your ribs pushing your hands to the sides, when you exhale just relax and feel the ribs come back down.

core muscles crossfit

Transverse Abdominis

The transverse is the deepest layer of the abdominals and its function is to support and compress the abdominal organs. It has an important role in the lower back and pelvic stabilization.

core muscles crossfit

To feel this muscle lay on the floor facing downwards.

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You will feel your belly touching the floor when you inhale, when you exhale try to bring your belly up far from the floor. Push the air out making an “F” sound with your lips and focus on keeping a neutral spine whilst not activating other muscles other than the transverse. Also make sure you’re not moving the lower back.

transverse abdominis crossfit activation

Internal oblique

It supports and compresses the viscera and also flexes and rotates the trunk. It helps fight the IAP redirecting it up instead of down. A way of feeling it is doing a side plank.

External oblique

When activated it lowers the ribs on a deep exhalation, compresses the abdomen, flexes and rotates the trunk. You can also feel it while doing a side plank.

oblique ciore strength

Rectus Abdominis

It’s main function is to support and compress the abdominal contents it also flexes the trunk. Easy way of feeling it is to do a sit up.

crossfit core

Quadratus lumborum

It extends the lumbar spine (bilateral action), allows the trunk tilt (or hemipelvis elevation) and descends the 12th rib on expiration. It’s easy to feel it doing the hemipelvis rise, that way you can feel the differences between both sides. Bend your knee slightly so your hip crease can come down and feel the muscle stretching, then activate the QL and feel how the pelvis goes up.

pelvic floor core muscles


It’s action causes the hip and lumbar spine flexion. It collaborates in lordosis maintenance.

To feel it and check it’s strength, or weakness, you have to perform a hip flexion.

Do it standing, you’ll also see if you dissociate the movement of the hip from the lower back: if you raise the leg and immediately your lower back bends it means that you don’t dissociate the movement of the hip from the movement of the pelvis.

This lack of dissociation can cause lower back problems because in movements like step ups you’ll bend your lower back making your quadratus lumborum work instead of the glutes.

muscles psoas

Multifidus and Spine Erectors

These small muscles work during the extension, rotation and inclination of the vertebrae. They help maintain the posture of the spine.

You’ll feel them, on both sides of the spine, during deadlift movements.

multifidus spine erector

Pelvic floor muscles

The function of these muscles goes from supporting the stay in place of abdominal organs to assuring their proper function (urine and fecal continence).

They have an important role in sexual relationships and they help in the stability of the pelvis and lower back.

To feel them place your hand with the middle finger’s tip on the anus and the palm resting on the vulva, this is for women.

For men go “from behind”, placing the middle finger’s tip in between the testicles and the anus. Once you’ve placed the hand properly contract like when you feel the urge to go to the bathroom and you don’t want to go. You have to feel the anus contracting and the vulva going up and separating from the palm of the hand; in men you’ll feel tha contraction of the anus and also the testicles and penis coming backwards.

If you don’t feel it consider checking a physiotherapist specialized in the pelvic floor.

what muscles pelvic floor

Obturator Internus

The obturator is an external rotator of the hip. It abducts the femur when the leg is in flexion and helps support the viscera. You can check it by stretching it and determining if it’s shortened. Lay down on the floor and place your feet wide on the sides, let the knees touch each other and check the tightness inside the hips.

core muscles importance

Now that you can locate and recognize some of the muscles that form the Core we’ll see in part II how to properly strengthen them in order to keep them strong and healthy.

Article written by TJ García