Core
The core is the group of muscles that control the trunk: rectus abdominis, the obliques, transverse abdominis, the spinal erectors, the diaphragm and the pelvic floor. Its main job is resisting unwanted movement of the spine and transferring force between the upper and lower body.
Core: what is it?
Core is a coaching word rather than an anatomical one, which is why it gets used loosely. The useful definition is functional: every muscle that can influence the position of the trunk, from the diaphragm above to the pelvic floor below, and from the abdominals at the front to the erectors and quadratus lumborum at the back. What unites them is not that they produce big movements, but that they mostly prevent them. A squat, a carry, a press and a sprint all load the core in the same way, by asking it to keep the trunk where it is while the limbs do the work.
What the core is made of
Rectus abdominis, the visible six-pack muscle, flexes the trunk and resists extension. The internal and external obliques rotate and side-bend the trunk and resist both. Transverse abdominis wraps horizontally and increases intra-abdominal pressure rather than producing movement. Behind them, the erector spinae extend the spine and resist flexion, and quadratus lumborum contributes to side-bending and pelvic control.
The two ends matter as much as the walls. The diaphragm forms the roof and the pelvic floor the base of a pressurized cylinder. When a client takes a breath into the belly and braces, the whole cylinder stiffens, and the spine has something to work against. That is why breathing instruction is part of core training rather than an add-on.
Train it by what it resists
The clearest way to program the core is by the direction of the force it has to resist. Four categories cover almost everything, and a program that includes all four rarely leaves gaps.
| Category | What it resists | Example exercises | Typical prescription |
|---|---|---|---|
| Anti-extension | The lower back arching | Plank, dead bug, ab wheel, hollow hold | 20-45 seconds or 8-12 reps |
| Anti-lateral flexion | The trunk bending sideways | Suitcase carry, side plank | 20-40 m or 20-45 seconds per side |
| Anti-rotation | The trunk twisting | Pallof press, half-kneeling anti-rotation hold | 8-12 reps or 20-30 seconds per side |
| Flexion and rotation | Producing movement, not resisting it | Cable crunch, hanging leg raise, cable woodchop | 10-20 reps |
Why endless crunches do not build a core
Crunches train trunk flexion, one of four categories, and only through a short range. A client can do hundreds and still lose their spinal position under a loaded carry, because nothing in the exercise ever asked them to resist a force. Adding a suitcase carry and a Pallof press to the same session covers more ground than tripling the crunch volume.
The second thing crunches do not do is transfer. Force in a squat, a press or a throw passes through the trunk, and if it leaks there, the limb work suffers. Loaded carries, heavy hinges and single-arm work train that transfer directly, which is why the strongest core training in most programs is not labelled core training at all.
Core work and lower back pain
Coaches see this constantly, and the honest position is limited. Trunk strength and endurance are worth building, and many clients with a history of back discomfort tolerate loading better once they can hold a neutral position under fatigue. That is a good reason to program it. It is not a reason to promise that a plank will fix a back.
What is practical: build endurance before load, keep the spine in a position the client can control, and progress by adding time, lever length or external load rather than by adding range. Pain that is persistent, radiating, or getting worse belongs with a clinician, and training continues around it rather than through it.
Key takeaways
- The core is a cylinder: abdominals, obliques, erectors, diaphragm and pelvic floor.
- Its main job is resisting movement, not producing it.
- Program by category: anti-extension, anti-lateral flexion, anti-rotation, then flexion.
- Carries and heavy compound lifts are core training even when they are not labelled that way.
Frequently asked questions
Is the core the same as the abs?
No. Abs usually means rectus abdominis, the muscle you can see. The core includes that plus the obliques, transverse abdominis, the spinal erectors, quadratus lumborum, the diaphragm and the pelvic floor. Training only the front of the cylinder leaves the rest of it undertrained.
How often should the core be trained?
Two to four short sessions a week is plenty, and they can be attached to the end of other workouts. Core muscles recover quickly, so frequency matters more than duration. Ten focused minutes across two or three exercise categories beats a long dedicated session once a week.
Do I need direct core work if I squat and deadlift heavy?
Heavy compound lifts do load the trunk substantially, particularly in anti-extension and anti-lateral flexion. What they miss is anti-rotation and controlled trunk flexion. A Pallof press and a loaded carry cover the gap in a few minutes a week.
Updated August 28, 2026
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