The pelvic floor is a hammock-like set of muscles that make up the bottom part of your core. They span from the pubic bone in the front, tailbone in the back, and reach to the sit bones and even the hips. These muscles function to support the pelvic organs, the spine, and the hips. They also help with the functional control of bowel movements, urination, and sexual activities.
To find these muscles you can produce a contraction by pretending you are trying to stop the stream of urine or holding back gas.
Also, try this exercise to feel the pelvic floor muscles move with your breath:
Step 1: Move into a seated, laying on your back, or a child’s pose position.
Step 2: take a deep breath that allows your belly to expand
Step 3: notice the pelvic floor stretch, expand, and/or move down
Step 4: exhale slowly
Step 5: notice the pelvic floor muscles lift, engage and/or move up
Your diaphragm and pelvic floor work very well together. The diaphragm is dome shaped at rest. When your diaphragm contracts, it flattens, drawing air into the lungs. This also causes the pressure in the abdomen to shift downwards, therefore the pelvic floor muscles stretch to accommodate for this shift. As you breath out, the diaphragm returns to that resting dome shape and the pelvic floor muscles contract slightly to where they need to be at rest.
Check out this great post that talks more about what exactly your pelvic floor is, courtesy of Athlete’s Care: