Which Twitch?

By Riva Preil

The pelvic floor muscles are composed of two different types of muscle fibers which can be thought of as two “speeds.” Approximately 70% of the pelvic floor muscle fibers are slow-twitch or slow-contraction fibers. The remaining 30% are fast-twitch fibers. The slow twitch fibers fuel endurance. They are the marathoners of muscles, providing support and resisting fatigue. Think of the muscles in your lower back: they are mostly slow twitch fibers that can work for a long time without tiring. That’s essential, because these are the muscles responsible for helping keep you upright. The slow-twitch fibers that comprise the bulk of your pelvic floor are the slow-to-tire, persistently supportive muscles.

On the other hand, fast-twitch fibers provide the swift forcefulness of sprinters. The ocular muscles that move your eyes, for example, are fast-twitch muscles. In the pelvic floor, the fast-twitch muscles assist in controlling the contraction and relaxation that open and close the bladder and bowel and that are involved in sexual function.

While both types of muscle fibers lost strength as the body ages, the fast-twitch fibers do so more readily. The slow-twitch muscles that make the pelvic floor a center of endurance and support generally maintain their power and function longer, unless there is trauma or injury. In a sense, the power to endure remains while the power to perform some of the pelvic floor’s key functions can diminish. That’s natural! As we get older, our powers diminish. That’s why it’s so important to stay fit for as long as we can; physical strength and vigor are the best defense against the aging process. If you have any questions regarding how to maintain a healthy and strong pelvic floor (ex. post partum mother or post abdominal surgery) please contact us at Beyond Basics Physical Therapy– we are happy to help!

Adapted from Heal Pelvic Pain, by Amy Stein

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