The pelvic floor is a group of muscles that sits within the pelvis. They are "bowl-shaped" and work to support our lower organs. The urethra, vagina and rectum all pass through the pelvic floor. This is why the pelvic floor can play a role in causing bladder leaking, discomfort during intercourse, constipation, diarrhea and uterine prolapse. The muscle strength and resting muscle tone can either help or hinder these conditions.
Naturally, the pelvic floor and the diaphragm work together. It is when these two muscles groups become out of sync that problems "don't resolve on their own."
Sneezing is a great example of when these two muscles don't work together. A sneeze is a forced exhale, during exhalation the diaphragm and pelvic floor should both rise. However, if pressure is forced downward, it can result in bladder leaking.
Pressure management is the key to a healthy pelvic floor.