Back extensions don't train your spinal erectors.
Back extensions may be the greatest fallacy in training, at least when it comes to the way they're commonly applied.
Often prescribed as a means to "build" the spinal erectors, the training rationale attempts a parallel between the spinal erectors and the "core 4" ab musculature. This proposition claims that a heavy axial load will allow an athlete to "squeeze" their spine erectors in an isometric mechanic, not dissimilar to core bracing.
In reality, it doesn't work this way. It's just not possible to contract your spinal erectors voluntarily.
Deep spine muscles can only contract reactively.
The muscles of the deep spine are innervated in a significantly different way from other muscles. As an extremely oversimplified explanation:
While "regular" muscles receive input as voluntary movement signals from the brain, the deep spine muscles only receive input as sensory feedback directly from the spine.
This means that the deep spine muscles are purely reactive- they contract only when the foregoing sensory feedback mechanism receives a relevant signal.
The rabbit hole explaining this complex mechanism runs deep, but for the purposes of this conversation, this level of granularity will suffice. (We explore the innervation and training of deep spine musculature further in the Level 1 course.
So with the above in mind, how do we train the spinal erectors?
Training relies on forcing reactive contraction.
There are a few useful interventions we can apply, but they all boil down to the same core concept: orienting the spine and synergistic musculature in such a way that forces sensory feedback to be supplied as input to the erector neural pathway.
The deep spine muscles contract much more reactively to load, particularly in certain positions. With this in mind, exercise selection, positional bias, and time are your major levers to pull. Projecting these onto a training program, we have the a few strategies we can use to effectively train spinal erectors:
- Isometrics
- Synergist Disadvantage
- Segmentation
${component=BasicCard}Isometrics
Implementing isometrics entails holding a relatively neutral spine against a consistent perpendicular force (i.e. gravity via the load), which tries to round you out of a solid brace. The key training mechanism at play here is time - holding this posture with a heavy load will inevitably shift force management responsibilities to the deep spine musculature.
Isometrics are a highly effective and massively scalable spinal erector training tool, owing to their their extremely high loadability. An extensive collection of exercises feature an isometric segment that fits the bill, and many of them are loaded heavily. Thanks to this generous range of loadability, isometrics allow for the progressive overload of spinal erectors in step with progressing other strength and hypertrophy training goals.
${component=BasicCard}Synergist Disadvantage
Harkening back to last week's conversion about "advantaging and disadvantaging" muscles, synergist disadvantage involves identifying muscles that would typically contribute to buffering spinal forces, and deliberately orienting those muscles in a position of mechanical disadvantage. In this context, "mechanical disadvantage" means a state in which these muscles are less levered, and less able to contribute to force buffering demands.
As a consequence of synergist disadvantage, force buffering responsibilities shift to the spinal erectors.
${component=BasicCard}Segmentation
As the name suggests, segmentation involves extending the spine against an external load in a progressive vertebrae-by-vertebrae fashion. In the fully-flexed position, other muscles that can contribute to spinal stability (ex. lats, traps) are placed at a relative disadvantage, allowing for tension to be placed across the full array of erectors.
Segmentation is the least loadable but easiest-to-access movement strategy for spinal erector training. It also comes with safety considerations, which we'll talk about below.
How to properly integrate spinal erector training.
In light of the above, we know that the deep spine muscles can only be trained in an indirect manner. That said, "indirect" does not mean "insignificant"- not by any means. With the wide array of training tools at our disposal, training deep spine musculature is very much possible, reasonably straightforward, and often seamlessly coherent with training other goals.
Before we go any further, a word of caution: the deep spine muscles are your last line of defence for spinal stability. Training these muscles often means deliberately inhibiting other spinal stabilizers, which leaves force buffering responsibilities up to the erectors. Should the erectors fail to manage these forces, that's it- force shifts to non-contractile structure (i.e. the facet joints of the spine). This is where things can go very, very wrong.
With that in mind, be cognizant of the risk involved in deliberate spinal erector training. As fatigue sets in, it becomes progressively easier for the spine drift into a compromised position under load. As a general disclaimer, don't do anything that brings about discomfort or causes injury, and always be mindful of the relative risk involved.
${component=Step}Use heavy hinge style exercises to apply the isometric strategy.
Select exercises that involve holding a static trunk posture against external forces that pull your spine into flexion. There are countless exercises that fit this bill, many of which you already use for other reasons.
Anything resembling a hinge is a good candidate- especially as many hinges are extremely loadable. With that in mind, RDLs and Barbell Rows both make for great choices.
RDLs focus on exposure primarily through the isometric management of absolute load. Double down on erector training by integrating a pause at the bottom of the rep.
Barbell rows focuses on exposure through time; they're less loadable, but the entire set is performed in a posture that implicates spinal erector involvement.
Regardless of which exercises you use, the core points of performance are the same: load it up, maintain a neutral spine, and avoid hyperextension (particularly important, as hyperextension would dampen deep spine sensory feedback input, attenuating recruitment).
${component=Step}Inhibit the lats; use specific implements to keep execution simple.
When considering which synergists to disadvantage in the context of deep spine training, we primarily focus on the lats. Their enormous size and expansive origin allows them to function as potent spine stabilizers.
Select exercises (or integrate execution techniques) that place the lats at a point of mechanical disadvantage, and involve holding a static trunk posture against external forces that pull your spine into flexion (as with the isolation strategy).
The Safety Squat Bar is an excellent piece of equipment for accommodating this very thing. Use the SSB to perform good mornings, pulling the handles of the SSB down. The act of pulling the handles down should round your upper back slightly, disadvantaging the lats.
${component=Step}Apply spinal segmentation conservatively; start slow with light loads.
Truthfully, for most people, segmentation does not make for a super productive spinal erector training strategy. There are rather apparent safety risks involved in deliberately flexing and extending the spine under axial load, and it takes quite a bit of prudence to ensure that these risks are well managed. Furthermore, exercise options are limited, and generally don't offer much of a runway of progression. That said, it's still a valid strategy, and can been implemented to at least level of some success.
Of exercises incorporating spinal segmentation, the Jefferson Curl is the most well-known and readily-accessible, requiring no specialized equipment. Begin the eccentric phase by protracting your scapulae, and "rolling" your shoulders towards your chest- think like you're rolling a up a rug. As you descend, progressively flex your spine vertebrae-by-vertebrae, top to bottom. Perform the exact inverse of these actions on the way up.
Again, since we're dealing with flexing/extending the spine under axial load, it's best to start slow - 2-3 sets with the barbell alone will be plenty.
The visual appearance of this exercise falsely suggests that it "works" the spinal erectors the same way that a bicep curl "works" the bicep- as if the deep spine muscles effectively "lift the weight" by extending the spine. This is absolutely not the case- we know that deep spine muscles are not under our voluntary control. Voluntarily flexing and extending the spine doesn't change that fact.
In the segmentation strategy, deep spine muscles don't derive training stimulus directly from the action of flexing and extending the spine. Rather, they get training stimulus incidentally, as a consequence of spinal orientation: the aforementioned sensory feedback mechanism autonomically triggers contractions in response to specific vertebral orientation. The resultant training mechanism is extremely similar to that of the other strategies- indirect and incidental.