Slow and Fast Twitch Muscle Fibers Within Our Pelvic Floor - What They Are and How to Work Them
Have you ever heard of slow twitch and fast twitch muscle fibers? Muscles that are predominantly made up of fast twitch muscle fibers are our quick reacting, higher contractile force muscles that fatigue rather quickly. Muscles made up of predominantly slow twitch muscle fibers are our less explosive muscles that are much longer lasting than their counterpart. You often hear of these two types of muscle fibers when comparing track sprinters to marathon runners. It may seem strange to think of slow and fast twitch muscle fibers within the 4 layers of our pelvic floor muscles but they are there.
It is this combination of slow and fast twitch muscle fibers that requires us to work, not only the quick flicks or quick contractions of the sphincter muscles of our pelvic floor, but also the steady, endurance of the levator ani muscles.
Let’s take a quick review of the layers of the pelvic floor. The outermost layer is our anal sphincter. The contraction of this muscle is the easiest to feel because it is superficial and can be contracted by squeezing our sphincter muscle as if we want to stop the passing of gas.
The second layer is our urogenital triangle which is made up of 3 muscles that are mostly sexual in function. Even though this layer doesn’t play a huge role in maintaining continence, it is one of the 4 layers of our pelivc floor that are all interconnected with fascia and tendinous tissue. The overall strength of our pelvic floor depends on the ability to contract all 4 layers of muscles.
The third layer is our urovaginal sphincter which forms a figure eight around our vaginal and urethral openings. We can contract this muscle by squeezing as if to stop the flow of urine.
Finally, the 4th and deepest layer of our pelvic floor is the levator ani. This is the group of muscles that is often described as our pelvic bowl or our pelvic sling that runs from our pubic bone to our tail bone.
Taking a closer look at the muscles of our pelvic floor, we begin to recognize fast and slow twitch muscle fibers. Within our relatively superficial sphincter muscles, used to stop the flow of urine or the passing of gas, we can recognize the presence of fast twitch fibers. They can contract quickly and with significant force when we cough or sneeze. Conversely, we can recognize the predominance of slow twitch muscle fibers within our levator ani muscles. They are part of our core stabilizing muscles that are always on. They cradle our bowel, bladder, and uterus, and with good tone, squeeze on the pathway through which urine travels from the bladder to our urethral opening.
It is important that we maintain good tone in our levator ani muscles to help support our bowel, bladder, and uterus, and to prevent urine from leaking out of our bladder involuntarily. This is why a big part of pelvic floor strengthening involves the muscle action of elevating our pelvic floor and holding for an extended count. We have to work the slow twitch fibers of our levator ani muscles daily to maintain that healthy tone as we age and undergo trauma and stresses such as childbirth, abdominal surgery, heavy lifting, hormone changes, or obesity. It is also important to work the fast twitch fibers within our sphincter muscles. Our sphincter muscles can contract with significant force when we cough, laugh, sneeze, jump, etc. These fibers don’t require the hold as much as a quick contraction and release in a repetitive fashion.
Knowing the importance of working both types of muscle fibers within our pelvic floor muscles, let’s review an optimal kegel sequence that will work both the slow twitch and the fast twitch muscle fibers. First, to work our endurance, squeeze your pelvic floor muscles as if to stop the flow of urine or the passing of gas. Now elevate your pelvic floor up into your pelvic outlet. Visualize a string attached from your belly button down to your pelvic floor and you are attempting to draw it up throughout a full 8 count. Then release your pelvic floor muscles, allowing them to completely relax. Now work the quick reaction of your fast twitch fibers by squeezing your sphincter muscles through 4 quick contractions. Squeeze as if to stop the flow of urine or the passing of gas to a quick rhythm of “contract-relax-contract-relax-contract-relax-contract-relax.” With that entire sequence of an 8 count elevation and hold followed by the quick contractions, you have completed one kegel sequence. Complete a total of 8 kegel sequences every day to maintain strength and tone of both the fast and slow twitch muscle fibers of your pelvic floor.
Tasha Mulligan MPT, ATC, CSCS
Creator: Hab It: Pelvic Floor dvd
Tasha wrote for HealthCentral as a health professional for Incontinence.