The Trunk Isn't Always a Brace

Walk through the core section of almost any training program and you’ll find the same handful of exercises. Planks, side planks, dead bugs, bird dogs, Pallof presses, suitcase carries. They’re good exercises, and I use most of them. But notice what they have in common: every one of them is about stopping the trunk from moving. Resist extension, resist rotation, resist side-bending, hold still while something else happens.

Then watch someone throw a ball, serve a tennis ball, swing a golf club, or throw a kick. The trunk in those movements is anything but still. It flexes, extends, rotates, and side-bends, often all within a fraction of a second, and a lot of the power comes from exactly that motion. Somewhere between those two pictures, the fitness industry decided the trunk’s main job is to stay rigid. I think that’s half the story at best, and the half we keep training is the half most people already get plenty of.

Where Bracing Came From

A lot of modern core training traces back to Stu McGill, and I want to be clear about where I stand on him. McGill is a genius. He has done more to help people understand the spine than almost anyone, and he isn’t against training the trunk. His approach is more regressed than mine because his model is built around a specific goal: getting people completely out of pain, as quickly as possible. That’s why you have the McGill curl-up, the bird dog, and the side bridge. They’re easy to learn, hard to do badly, and they let someone with a cranky back train without provoking it. And his method clearly can work.

Bracing is also a real skill. When you squat something heavy, carry something awkward, or take a hit, you want your trunk stiff. Stiffness lets force pass from the ground to the bar (or from your legs to your arms) without leaking out through the middle. Anyone who has tried to deadlift with a soft trunk knows how quickly that goes wrong.

My concern is what happens after the pain is gone. If the trunk only ever learns to stiffen, we never teach it how to distribute force along the spinal column during the movements real life actually asks for: reaching, twisting, picking things up off the floor at odd angles, throwing, running. Getting someone out of pain with a regressed approach is a win. Stopping there can kick the can down the road.

How It Became Dogma

The bigger problem is what the industry did with the idea.

A lot of personal training certifications teach some version of “stabilize the trunk first” as the way to progress someone who’s just starting out. I understand why. It’s simple, it’s safe, it’s easy to teach to a room full of new trainers, and it gives them a clear first step. But the average trainer doesn’t really understand the ideas behind it. What gets passed down is a shortcut: if someone can’t brace, they must be “disorganized” in how they move, so the fix is more bracing. Planks until further notice.

The reality is that bodies aren’t uniformly under-braced. Some places need more stiffness; other places need more movement. And when I say movement, I don’t mean the arms and legs. It’s often other segments of the spine itself that aren’t doing their share of the work. Calling someone “disorganized” and handing them more anti-movement drills treats a distribution problem as if it were a strength problem, and it doesn’t give the stuck segments anything to do. We shouldn’t shrink ourselves to just one piece of it.

What the Spine Is Built to Do

Look at how the spine is put together and it’s hard to come away thinking it was designed to be a rigid post. It’s a stack of more than twenty movable segments, each contributing a little motion, so the whole column can flex, extend, rotate, and side-bend. That’s a strange design for something meant to stay still. It makes much more sense for something meant to share motion, so no single segment has to do too much.

One of the more useful lenses for this comes from Serge Gracovetsky, an engineer who spent years studying the lumbar spine. His spinal engine hypothesis proposes that the spine is a primary driver of human locomotion, with the legs expressing and amplifying motion that the trunk organizes, rather than the trunk simply riding along on top of the legs (1). I think the mechanics make sense. I also don’t think they’re the be-all, end-all. Spinal engine theory is a framework, and a good one; it can help you improve someone’s walking and gait efficiency, especially if you know what to look for. The catch is that knowing what to look for is genuinely hard. Seeing how a spine is (or isn’t) contributing to someone’s gait takes a trained eye and a lot of repetitions, and it’s easy to see what you expect to see.

What the framework gets right, either way, is the relationship. The trunk and the hips are supposed to work together, constantly, in more than one direction. A trunk that has only been trained to resist motion has a hard time joining that conversation, and the motion it won’t produce gets pushed somewhere else.

Hinge Points

“Somewhere else” usually has a specific address. When some segments of the spine don’t move well, the motion piles up at the segments that do. Those are hinge points: one or two levels doing a disproportionate share of the work while the segments around them stay quiet.

The clearest illustration comes from somewhere I wouldn’t normally look for training advice: spinal fusion surgery. When surgeons fuse a lumbar segment, they remove its motion entirely, and the research is fairly consistent that the segments next to the fusion pick up compensatory motion. A 2025 systematic review of 87 publications found that immobilization from fusion led to increased motion at the adjacent segments, although the authors were careful to say the causal link between that extra motion and later degeneration remains inconclusive (2). The principle is simple: the spine still has to produce the movement you ask of it, so when one part stops contributing, its neighbors make up the difference.

You don’t need surgery for that to happen. Take rotational training, like throwing a medicine ball against a wall. The throw asks for a lot of rotation, and a healthy thoracic spine is built to provide much of it, spread across many segments. If parts of the thoracic spine are effectively immobilized (stiff from years of not being asked to rotate), the throw still happens. The rotation just gets taken from wherever it’s available, and the hinge points pick up the work. From the outside it can look like a decent throw. Underneath, a few segments are absorbing load that should have been shared by a dozen. That’s compensation, and calling it efficiency would be generous.

A stiff segment isn’t the same as a fused one, and I’d be overreaching to say the fusion research proves that hinge points in a healthy spine cause problems. But the mechanism is the same, and it’s the reason I care about segmental movement rather than just stiffness. Bracing harder doesn’t fix a hinge point. It just locks in whichever segments were already doing the moving.

The Fear of Moving the Spine

A lot of the resistance to training spinal movement comes from fear, specifically the fear of flexion. For years the standard advice was to keep the back flat when you lift, never round, protect the discs. That advice came from somewhere reasonable, including lab work on how spinal tissues fail under repeated loading. But it’s worth looking at what the human research found.

A 2020 systematic review and meta-analysis found no prospective association between how much people flexed their low backs when lifting and later developing low back pain, and no difference in peak lumbar flexion between people with and without back pain (3). The authors concluded that the common advice to avoid flexion when lifting isn’t supported by the evidence. That doesn’t make loaded flexion risk-free; the studies were mostly of modest quality and used fairly light loads, so I wouldn’t stretch the finding to max-effort deadlifts with a rounded back. But it does take some air out of the idea that a moving spine is a fragile one.

The evidence on the stabilization approach itself tells a similar story. A Cochrane review of motor control exercise (training built around activating and coordinating the deep trunk muscles to support the spine) found it helped people with chronic low back pain more than minimal intervention, but it wasn’t superior to other forms of exercise, and the authors suggested the choice of exercise should probably come down to things like preference, cost, and safety (4). Stabilization training works about as well as other reasonable approaches. It’s one good option. The evidence doesn’t make it the only one.

What Training the Spine Can Look Like

There are a lot of ways to train the spine, and I don’t think there’s one right program. The more useful thing to understand is the difference between two kinds of trunk exercise. A plank is an isometric: the spine holds one position while the muscles around it work to keep it there. A fully loaded spine exercise asks the spine itself to move through its range, under load, and to control that movement on the way down and the way back. Both have value. Most programs only include the first.

A good place to start is spinal CARs: slow, controlled rotations through the whole column, trying to move it one segment at a time. They show you where the spine moves well and where it moves as a single block (most people find more blocks than they expected), and they keep that motion available. I go into what CARs are and aren’t good for in What CARs Are Actually For. Once they’re owned, they can be loaded.

From there, each direction can be trained under load. For flexion, the Jefferson curl is the classic example: standing on a box and rolling down through the spine one segment at a time while holding a weight, then rolling back up. It deserves respect; start very light and progress slowly. Sit-up eccentrics and reverse sit-up eccentrics (lowering the trunk down segment by segment, or lowering the pelvis and low back down from the other end) train flexion with control in a different orientation. For extension, back extensions on a 45-degree bench or a glute-ham developer, done by articulating through the spine rather than hinging from the hips with a rigid back, and reverse hypers both work well. For lateral flexion, loaded side bends, standing or turned sideways on a 45-degree bench, let the spine bend and return against load. Rotation can be loaded with cable or landmine work and, eventually, medicine ball throws.

The intent matters more than the exercise list. The goal is dynamic, truly segmental efficiency: a spine where every region contributes its share, in every direction, with control. If someone’s side bend all happens at one level, or their eccentric sit-up drops through a single segment, that’s a hinge point showing itself, and the work is to get the quiet segments contributing. Then that control has to connect to the hips, through locomotion, rotation, and throwing, so the trunk and the hips organize movement together instead of one compensating for the other. If the hips are the part that isn’t contributing, Hip Internal Rotation: The Range Most People Lose is a good place to start.

None of this replaces bracing. You still want to know how to stiffen your trunk under a heavy bar. The difference is that bracing becomes a choice you make when the task calls for it, and that choice only exists if your trunk can also do something else. That’s the same idea behind Mobility as Capacity, Not a Category: more options, more ways to solve a movement problem.

Who Should Be Careful

If you’re in an acute flare of back pain, a regressed, anti-movement approach is often exactly right for a while; that’s the situation McGill’s work was built for. Pain that radiates down a leg, numbness or tingling, weakness in the legs, or any change in bladder or bowel control is a reason to see a clinician promptly, not a reason to train through it. And people with hypermobile spines may need more control and stiffness rather than more motion, which is a different conversation (one the guest post When Stretching Makes Pain Worse gets into).

For everyone else, look at your core training and ask a simple question. How much of it teaches your trunk to move, and how much teaches it to stop moving? If the answer is almost all of the latter, you’re training one job of a structure that has at least two. The trunk is one of the most dynamic things we have. It’s our pillar for a reason, and treating it as something that only needs to stiffen leaves most of what it can do on the table.

References

1. Gracovetsky S. An Hypothesis for the Role of the Spine in Human Locomotion: A Challenge to Current Thinking. Journal of Biomedical Engineering. 1985;7:205-216.
2. Jokeit M, Tsagkaris C, et al. Impact of Iatrogenic Alterations on Adjacent Segment Degeneration After Lumbar Fusion Surgery: A Systematic Review. Journal of Orthopaedic Surgery and Research. 2025. https://doi.org/10.1186/s13018-025-05561-1
3. Saraceni N, et al. To Flex or Not to Flex? Is There a Relationship Between Lumbar Spine Flexion During Lifting and Low Back Pain? A Systematic Review With Meta-analysis. Journal of Orthopaedic & Sports Physical Therapy. 2020;50(3):121-130. https://pubmed.ncbi.nlm.nih.gov/31775556/
4. Saragiotto BT, Maher CG, Yamato TP, Costa LOP, Menezes Costa LC, Ostelo RWJG, Macedo LG. Motor Control Exercise for Chronic Non-specific Low-Back Pain. Cochrane Database of Systematic Reviews. 2016;(1):CD012004. https://doi.org/10.1002/14651858.CD012004