Issue link: https://www.massageandbodyworkdigital.com/i/1505456
FORCE TRANSMISSION: FASCIA AT WORK Whether you're carrying your massage table or twisting to reach your massage oil, your abdominal muscles contract to generate force. How can this muscle-generated force create stability and movement in the bone-free expanse of the belly? As it turns out, our muscles don't necessarily need bones for movement. What they do need is tissue that shares a particular property of bones: stiffness. Here's where the rectus sheath comes in. Every time your obliques and transversus abdominis muscles contract, they pull on their f lat tendons, which tension the rectus sheath. As the rectus sheath is tensioned, it stiffens, and Bam! you've got what you need for movement: a connective tissue framework that is stiff and tense for force transmission. No bones about it. But to have complex movement, we also need motor coordination. MOTOR COORDINATION: CROSSING THE MIDLINE Let's take a minute to feel how the abdominal muscles talk to each other to create motor coordination. Whether you're seated or standing, take a twist to the right, then to the left. When we twist, the EO of one side contracts at the same time as the IO of the opposite side, creating coordinated movement. How? The rectus sheath holds some clues. There's one part of the rectus sheath that's almost never left out of our anatomy books: the linea alba. At the midline, the f lat tendons of the EO, IO, and TrA from both the left and right sides merge, creating longitudinal reinforcement. Our anatomy books describe the linea alba as the insertion point for EO, IO, and TrA. When we zoom in, the collagen fibers of the linea alba tell an additional story. By zooming in to the level of collagen fibers, it's clear that the linea alba is not the end point for these muscles. Analyzing fiber-by-fiber, researchers found that fibers from every layer of the rectus sheath pass across the midline and even interweave strategically. 1 This three-dimensional meshwork of fibers allows both force transmission and communication with the opposite side (I mage 2). If we return to our twist, we now see that the EO and IO are connected by the fibers of their f lat tendons intermingling and crossing through the midline. The EO can feel the movement of the IO on the opposite side through its sensory nerves and vice versa, enabling motor coordination. Onto the rectus sheath's next feat—trunk stability. TRUNK STABILITY: FRONT, MEET YOUR BACK If you ask somebody to touch their abs, chances are they touch the front of their abdomen, or perhaps laterally along the waistline. But if they touch their low back, technically, they would also be touching their abs. Looking at the torso in cross- section, we see that the combined muscle and fascia of EO, IO, and TrA circle around L i s te n to T h e A B M P Po d c a s t a t a b m p.co m /p o d c a s t s o r w h e reve r yo u a cce s s yo u r favo r i te p o d c a s t s 69 TAKEAWAY: The rectus sheath is a multilayered fascial hub that allows force transmission, motor coordination, and stability in the trunk. Linea alba. In this image from the upper abdomen, we can clearly see collagen fibers in the anterior rectus sheath converging at, and crossing over, the midline, enabling communication between the two sides. While often depicted in drawings as a distinct structure, that is not how the linea alba is found in the body. The linea alba is continuous with the rectus sheath. Image courtesy of AnatomySCAPES.com. 2