The Truth About Core Training: Building Real Trunk Strength and Stability

By Dr. Jason Miller, PhD — Strength & Conditioning Specialist
(Excerpted from the NAT Global Campus course: “Resistance Training”)

If there’s one thing I’ve learned after years of working with athletes, therapists, and rehab professionals, it’s this: core training is one of the most misunderstood parts of strength and conditioning.

The “core” — or what we might more precisely call the trunk musculature — is not just about doing crunches or trying to carve out visible abs. It’s about stability, control, and efficient movement. In fact, most of the time, the job of your trunk muscles isn’t to move your spine at all — it’s to keep it from moving when it shouldn’t.

In this article, I want to unpack the science and practice behind training the trunk properly. We’ll talk about flexion, extension, rotation, and all those “anti” versions you’ve probably heard about: anti-rotation, anti-flexion, and anti-extension. More importantly, we’ll explore how to build a program that makes your clients stronger, safer, and more resilient — whether they’re recovering from injury, improving performance, or just trying to move better.

The Problem with How We Think About the Core

Let’s start with a bit of myth-busting.

When most people hear “core,” they think abs — and when they think abs, they picture crunches. Maybe planks if they’re a bit more modern. But the reality is that your trunk musculature includes dozens of muscles — from your rectus abdominis and obliques to your multifidi, erector spinae, diaphragm, and even the pelvic floor. These muscles form an integrated system that stabilizes your spine and transfers force between your upper and lower body.

When you swing a golf club, sprint down a field, or even just stand up from a chair, your core doesn’t primarily create motion — it controls it. It prevents your spine from collapsing or twisting out of line while your limbs move around it.

So if your trunk training program focuses only on producing motion (like crunches and sit-ups), you’re missing half the picture.

Understanding Trunk Movement Patterns

For simplicity, I like to group trunk training into six fundamental categories:

1. Flexion – bending forward (think crunch).

2. Extension – bending backward (think back extension).

3. Rotation – twisting (think Russian twist or cable chop).

4. Anti-Flexion – resisting forward bend (think deadlift setup).

5. Anti-Extension – resisting over-arching the lower back (think plank).

6. Anti-Rotation – resisting twist (think Pallof press).

The first three are about generating movement. The last three are about controlling it.
And it’s that control — the ability to stabilize and resist unwanted movement — that truly defines a strong, functional core.

Why Spot Reduction Is a Myth (and Why It Matters)

We’ve all seen it: someone banging out hundreds of crunches hoping to “burn off” belly fat. I hate to break it to you, but spot reduction doesn’t work. You can’t selectively burn fat from one area by training that area. The visibility of your abs has far more to do with nutrition and overall body composition than with how many crunches you do.

That doesn’t mean crunches are useless — they just need to be used intelligently. When you understand their role in the broader system of trunk training, you start to see where they fit. Crunches can help strengthen the anterior wall of the abdomen, but they shouldn’t dominate your program.

Flexion Training: More Than Just Crunches

When training flexion, traditional crunches and sit-ups are fine — if done properly and for the right reasons. The key is control, not momentum.

I like to cue clients to open the abdominal wall, then squeeze down slowly — keeping their heels close to the glutes to take pressure off the lumbar spine. That subtle adjustment can make a big difference in comfort and safety.

For clients with an anterior pelvic tilt, I sometimes use a lower bias crunch, rolling the hips slightly off the floor to help recruit the lower portion of the rectus abdominis. You can’t truly isolate the “lower abs,” but you can bias them with better pelvic positioning.

What matters most is that the spine moves under control — not jerking or yanking. Think quality over quantity.

Anti-Flexion: Controlling the Descent

Anti-flexion is about resisting forward movement. One great example is the med-ball slam. But done wrong, it just turns into an upper-body hinge.

Instead, I teach clients to generate power from the hips while the trunk resists collapse. As you lift the ball overhead, stay tall — don’t let your low back over-extend. Then as you slam it down, engage your abs to control that rapid flexion moment.

Another brilliant anti-flexion tool is the ab-roller. Used properly, it creates a huge eccentric challenge for the anterior core. The trick is to drive your hips toward the wheel as you roll out, not just extend from your arms. That keeps the load on the trunk rather than dumping it into the low back.

If you can perform slow, controlled ab-rollouts through a full range of motion, you’re displaying serious trunk strength.

Rotation and Anti-Rotation: Finding Balance

Rotational power is important, but in most real-life movement, it’s controlled rotation that keeps us healthy.

Classic cable or band chops are great tools — as long as you think about what you’re trying to achieve. Instead of cranking through reps, focus on controlling both the movement and the return.

I love half-kneeling chops for this reason. When you kneel with the inside knee up (toward the anchor point), you can’t use your hips to cheat — your trunk has to do the work. Start high-to-low, then progress to low-to-high patterns.

You can also flip these into anti-rotation drills by holding the cable static, resisting the urge to twist. Try a simple Pallof press variation: stand tall, brace your core, and press the band straight out from your chest, holding it steady as it tries to pull you sideways. That’s your core stabilizing in real time.

Extension and Anti-Extension: The Forgotten Muscles

While the anterior core gets all the attention, the posterior chain — your erector spinae, multifidi, glutes, and hamstrings — is equally important.

Exercises like bird-dogs are phenomenal for teaching spinal control. When done correctly, they activate the deep stabilizers that protect your back during lifting and athletic movement.

Here’s how I coach it:
Start on all fours, hands under shoulders, knees under hips. Keep a neutral spine — no sagging, no rounding. Extend one arm and the opposite leg, hold for a few seconds, then return with control. Progress it by adding small weights, mini-band resistance, or by “waving” your extended limb side-to-side.

You’ll quickly see how challenging it is to maintain trunk control under small perturbations.

Then we have planks — perhaps the most popular anti-extension exercise. But here’s the problem: static planks only go so far. The human spine doesn’t just hold one position; it moves, stabilizes, and responds to forces dynamically.

So, instead of holding a three-minute plank, try progressing it. Move your arms. Tap your shoulders. Add band pulls. Lift one foot. Rotate slightly and return. That’s where the real stability work happens — when your core has to react.

Side Planks: Rotational Control in the Frontal Plane

Side planks are another underappreciated gem. They target the obliques, quadratus lumborum, and deep lateral stabilizers.

You can hold them statically to start, but once you’ve got control, start progressing: add reach-throughs, leg lifts, or even banded rows from the top position. Each progression teaches your trunk to resist rotation and lateral flexion while maintaining a solid alignment from head to toe.

Reverse Hypers and Posterior Chain Progressions

When we talk trunk, we can’t ignore the erector spinae and glute complex. These muscles provide the scaffolding for everything else.

The reverse hyperextension, whether on a machine or just off a bench, is one of the best ways to train this area. Lie face-down with your hips just off the edge and lift your legs in a slow, controlled motion. You can progress from simple tucks to flutters, marches, or “jumping jack” patterns — all while keeping tension in the posterior chain.

I’ve even used partner resistance — a light band around the ankles, gently tugged during the lift phase to create unpredictability. That trains reactive stability in the lumbar region, which is incredibly valuable for athletes.

Why Trunk Training Is About Control, Not Reps

The most common mistake I see? Treating trunk training like cardio.

High-rep ab work can have its place, but the trunk’s real job is endurance through control — the ability to resist motion over time, not to move rapidly over and over.

So I tell my athletes: Don’t count reps; count quality. Every repetition should be a demonstration of control.

If your goal is performance or injury prevention, trunk training should be programmed just like any other resistance training — with attention to load, time under tension, and progression. You wouldn’t have a client squat 200 reps at random — so don’t do that with crunches either.

Progressions That Make Sense

Every trunk exercise has a logical progression:

• Start simple, master control, then add perturbation.

• Move from static holds to dynamic movement.

• Add load only when stability is maintained.

A beginner might start with supine holds, dead bugs, and short planks.
An intermediate client might add chops, rollouts, and side planks with reach.
An advanced athlete might progress to rotational throws, banded perturbations, and loaded carries.

No matter the level, the focus stays the same: maintain spinal integrity while the limbs move.

Common Coaching Cues

Here are a few of my favorite cues you’ll hear me repeat again and again during trunk work:

• “Stay tall, not tight.” (Encourages alignment without rigidity.)

• “Brace like you’re about to be punched — but don’t stop breathing.”

• “Move from the hips, not the spine.”

• “Keep your ribs down and your pelvis neutral.”

• “Slow the return — control beats power every time.”

Good cues build body awareness. The goal isn’t to make the client stiff; it’s to help them coordinate movement so the trunk becomes a stable base for everything else.

Why Anti-Movement Training Matters in Sport and Life

Anti-movement training might sound counterintuitive, but it’s the foundation of performance.

Think about sprinting: your legs are moving explosively, but your torso stays controlled.
Think about throwing a ball: your hips rotate, your shoulders follow, but your trunk transmits force efficiently between them.
Even in simple daily tasks like carrying groceries or picking up a child, it’s your core that allows your limbs to move without compromising spinal safety.

That’s why anti-rotation and anti-extension drills are so powerful — they teach your body to handle the unpredictable. Life rarely happens in a perfect sagittal plane.

When and How to Program Trunk Work

In most of my programs, trunk training isn’t a separate “core day.” It’s integrated throughout.

You can pair core stability drills as fillers between compound lifts — for example, a bird-dog variation between sets of squats, or a side plank between presses. You can also include them as part of a movement prep or finisher depending on intensity.

For athletes, I often rotate the emphasis weekly — one week anti-rotation, another week anti-extension, and so on. That keeps variety high while progressively building stability in all planes.

The Real Goal: Controlled Power

Ultimately, we train the trunk not for aesthetics or isolation, but for integration.
A strong core isn’t one that moves wildly — it’s one that allows everything else to move efficiently.

When your trunk is stable, your lifts are safer, your running is smoother, and your movement feels effortless.

So stop chasing crunch counts and start chasing control.
Your spine, your clients, and your performance will all thank you.

Key Takeaways

• Core training is not about movement — it’s about controlling movement.

• Focus on anti-rotation, anti-flexion, and anti-extension as much as (or more than) traditional flexion and rotation.

• Train the trunk progressively: static → dynamic → loaded → reactive.

• Quality trumps quantity every time.

• Remember, nutrition defines how abs look — training defines how the trunk functions.

Ready to Learn More?

This article is adapted from my class within the Resistance Training course on NAT Global Campus, where we explore how to build strength systematically — from foundational movement to performance programming.

You’ll get in-depth video demonstrations, evidence-based instruction, and real-world progressions you can apply immediately in your gym, clinic, or studio.

Join us and keep learning smarter: NAT Global Campus – Resistance Training

Disclaimer

This content is for educational purposes only and should not replace professional assessment or medical advice. Always consider client readiness, movement ability, and contraindications when implementing any exercise.

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