40–50% of the average adult male is muscle, as is 30–40% of the average adult female. Muscles are so named because sometime around the early 1500’s, the rippling of bicep muscles while they flexed were observed to resemble small mice scampering under the skin. (The word musculus means “little mouse” in Latin.) It is easy to understand the workings of mouse-like muscles in an arm or leg. But what about one deep inside your back that looks more like a pencil?
“The multifidus muscle was formerly thought to be relatively unimportant based on its fairly small size. Our research shows that it’s actually the strongest muscle in the back because of its unique design. It’s like a long, skinny pencil packed with millions of tiny fibers.” So says Dr. Richard L. Lieber, Professor at UC San Diego’s Department of Orthopedic Surgery.
Cornerstone of Spinal Support and Back Health
The unusually designed multifidus muscle (the word multifidus means “with many branches”) lies deep within the back, along the spinal column. According to researchers at the University of California, San Diego, it may now be considered a cornerstone of spinal support and overall back health. Findings about the possibly significant role of this muscle are published in the January 2009 issue of the Journal of Bone and Joint Surgery.
Researchers discovered that the multifidus has a distinctive scaffold design entailing short fibers arranged in rods. These fibers are stiffer than any other in the body. Using methods of laser diffraction they developed for measuring internal properties of muscle during back surgery, they showed that the multifidus’ design functions as a stabilizer of the lumbar spine.
Importance of Minimally Invasive Surgery Highlighted
According to Steven R. Garfin, M.D., professor and chair of UCSD’s dept. of orthopaedic surgery, “The more we know about what muscles do, the better we can devise therapeutic interventions such as physical therapy to target specific muscles.”
Currently, surgery used to treat spinal disorders may in fact disrupt the multifidus muscle, possibly leading to destabilization and lower back pain. Minimally invasive spine surgery (MISS) aims to minimize surgical trauma to these muscles to preserve their function, Garfin explained.
The lumbar spine, or lower back, is susceptible to many pain inducing injuries and disorders, due to the fact that lumbar vertebrae carry the most body weight, and are subjected to the most force and stress along the spine. Muscular instability is a factor in many injuries and their ensuing chronic lower back pain.
“The multifidus back muscle keeps us vertical and takes pressure off the discs,” said Dr. Lieber. “When muscle function is poor due to back problems, support is lost.”
He goes on to explain that many muscles get weaker as they are extended. But researchers learned that, unlike all other muscles, the multifidus actually becomes stronger as it lengthens, when the spine flexes.
“The length of the sarcomere—the structure within the muscle cell where filaments overlap to produce the movements required for muscle contraction—is shorter in the multifidus than in any other muscle cell,” said lead author Samuel R. Ward. “But as it gets longer, for instance as a person leans forward, the multifidus actually strengthens.”
“Architectural Analysis and Intraoperative Measurements Demonstrate the Unique Design of the Multifidus Muscle for Lumbar Spine Stability”: Samuel R. Ward, PT, PhD, Choll W. Kim, MD, PhD, Carolyn M. Eng, BS, Lionel J. Gottschalk, IV, BS, Akihito Tomiya, MD, PhD, Steven R. Garfin, MD and Richard L. Lieber, PhD The Journal of Bone and Joint Surgery (American). 2009;91:176-185. doi:10.2106/JBJS.G.01311