This is an excerpt from Strength Training for All Body Types by Lee Boyce & Melody L. Schoenfeld.
You can think of the spine as the mission control center of every movement pattern. The reason is that the underlying goal of all major lifts, and many major muscles’ involvement in those lifts, is to protect the spine and the important role it plays in creating a healthy body. The spine is made up of three regions: the cervical region comprising 7 vertebrae, the thoracic region comprising 12 vertebrae, and the lumbar region comprising 5 vertebrae (figure 3.1). Each region has a different capability and responsibility for rotation, extension, and flexion (both laterally and sagittally).
The spine lives up to being a control center even more so because it encases the spinal cord, which directly communicates with the brain. Nerves that link to and innervate muscle tissue branch out from the spinal cord. In short, all of a lifter’s strength, function, and power capacity rely on proper function of the spine. Efficiently performing compound movements is contingent on the spine’s remaining in a proper position while under load.
Flexed Versus Neutral Versus Extended
So we’re all on the same page, it’s best to start by defining each of these spinal positions. A flexed spine refers to the segments of the vertebral column tilting to accommodate a rounded, or forward bending, position. Telling someone to reach down and touch their toes with straight knees will almost always result in a flexed spine—especially through the lumbar region. A neutral spine is the most desirable across most scenarios, where the vertebral column creates basically a straight line, encouraging a very braced core and a well-supported axial skeleton. An extended spine refers to the segments of the vertebral column tilting to accommodate a leaning back, or arching, position. For most people, this is easiest to attain in the lumbar region, especially since the lumbar region has a natural lordotic curve, or arch, to it.
In almost all cases, it’s not recommended for a lifter to perform a compound movement with a flexed spine. That doesn’t mean the second this happens an injury will be guaranteed—but it does mean the chances have increased. It’s an important distinction for an individual to grasp. As a lifter or coach, it’s easy to get stuck in the matrix of being a technique stickler who disallows any irregularities in form. Although it may guarantee a client’s safety, it might also hinder their abilities to perform what’s known as a “grind”—the phenomenon of pushing through a tough repetition and trusting the technique they have worked hard to earn. Time in the profession (and time spent training oneself) can be instrumental in finding a way to strike a balance between the grind and an unsafe movement. Even though this book doesn’t encourage overuse of the one-repetition max (1RM) for the general population, the concept of grinding and being closely married to absolutely perfect and flawless technique and positioning is still vital information for people looking for strength gains even in 3M, 5M, or even 8M ranges—specifically because reaching a new rep range max will probably mean a final rep that isn’t as clean technically as the first rep of that set.
Notwithstanding the preceding information, the ideal for most lifts would be a neutral spine because it promotes the greatest involvement of the musculature on both the front and rear sides of the structure. Remember: The glutes and hamstrings are posterior tilters of the pelvis, since their direction of contraction is downward. The lower abdominals contract upward from the front side of the body, which means when those muscles shorten, they harmonize with the glutes and hamstrings in creating a posterior pelvic tilt. It’s only sensible to keep these muscles involved and engaged during loaded exercises because they’ll support the lift—whatever it is. With that said, it’s important to understand how posterior tilting can act on the spine (figure 3.2).
A typical healthy spine will be softly shaped like the letter S when viewed from the side. That means a slight lordosis of the spine (extension) in the lumbar region. Going back to the involvement of the glutes, hamstrings, and lower abs when contracted, posterior pelvic tilting will remove that lumbar extension from the picture and neutralize the spinal position—a terrific starting position for vertical pushes and pulls.
Bearing load with an overly extended spine can potentiate risk in the same way and isn’t ideal when the force angle of the exercise isn’t in harmony with said extended spine (more on force angles later). Compression from spinal extension can happen just as easily as compression from spinal flexion, which only further drives home the idea of neutrality being king. In simple terms, compression happens most commonly under vertical loading—namely, standing exercises that involve weight. Bearing load in a standing exercise like a squat, overhead press, or deadlift applies downward stress forces on the spine that can be exacerbated when the spine is not held in a neutral position (i.e., flexed or extended). The discs between the vertebrae are at risk of getting pinched, or impinged, from the loading coupled with the vertebral misalignment, ultimately causing a disc herniation. The compressed region of the spine will pinch the disc and cause it to bulge outward toward the more open side of the vertebra, which results in very distinct pain for the lifter (who at this point would be very fittingly referred to as a patient).