7 Clues Your Client’s Weak Side Is a Brain Problem (Not a Strength Deficit)

If one side of your client’s body always hurts, collapses, or underperforms, it’s probably not their hip, shoulder, core, etc. It might start with their brain.

Most of us were trained to think biomechanical.

We were taught to strengthen weak sides, stretch tight muscles, and cue symmetry. And that education served us — because for decades, it was the best we had.

At NLN, we’re not here to tell you that the model is wrong. We’re here to give you a new lens — a neurological perspective that complements what you already know.

The industry has long emphasized unilateral training to fix asymmetries, which makes perfect sense. But we believe it's time to take that further. It's time to look beyond the muscle — and into the brain controlling it.

Because neuroscience is evolving.

We’ve learned more about the brain since 2005 than in all human history before that.

And now that applied neurology is accessible to coaches and therapists, we have an obligation to look again at the patterns we've seen for years... and ask deeper questions.

So this piece isn’t just about fixing the collapsing shoulder or unstable lunge. It’s about understanding the neural reason those patterns won’t go away — and what to do about it.

Because the same principle behind one-sided neurological deficits — when one hemisphere of the brain underperforms — also shows up in other frustrating client patterns:

The bad posture that keeps coming back.

The hip that keeps locking up.

The shoulder that flares up again after every deload.

Let’s be honest: how many times have we blamed it on tight hip flexors, sitting too much, or stress?

And yes — sitting and stress absolutely matter.

But we also need to go deeper. 

WE NEED TO TAKE RESPONSIBILITY AS THE PROFESSION THAT PEOPLE COME TO FOR HELP.

Now, more than ever, you will start seeing brain-based coaches, combined with therapy and training, being paid at the top of the health field because they took the time to learn the simplicity of brain science. 

This is what the Director of Education at Next Level Neuro, Matt Bush, calls one-side-itis — the recurring, same-sided breakdowns that won’t resolve with strength work alone.

It’s a neurological issue.

And once you understand how to apply neurology to your assessments and training, you’ll start to see why those stuck patterns keep repeating.

And more importantly — how to change them.

Understanding applied neurology DOES NOT require a neuroscience degree.  But it does require a new lens.

A shift in how we think about posture, pain, and performance.

Once you get the basics, it starts to make sense — and your client results will reflect it.

In the rehab and performance world, we’re taught to look for symmetry.

Squat evenly.

Load both limbs.

Strengthen the weak side.

But what if the problem isn’t the muscle? What if the root of that asymmetry is neurological?

Enter the concept of one-sided neurology – a brain-first lens that explains chronic one-sided pain, poor posture, and persistent strength imbalances that don’t respond to traditional training.

And yes, there’s a way to test for it. Train it. And resolve it fast.

Clue 1: One Brain, Two Hemispheres, Very Different Jobs

Your brain is not a mirror image.

Each hemisphere has different roles, and different pathways that descend into the body. More importantly, it controls the body ipsilaterally or contralaterally depending on the structure.

Here’s what you need to know:

• The PMRF (pontomedullary reticular formation) in your brainstem controls the same side of your body.

• Your cerebellum also connects same side to body.

• Your motor cortex mostly controls the opposite side.

So, if one side of the brainstem or cerebellum is underperforming, your client’s same-side body may collapse, feel weak, or move poorly — no matter how much you train it.

“You can’t coach a glute to fire if the brain that talks to it isn’t online. That’s the real asymmetry.” – Matt Bush

Clue 2: The Postural Patterns No One Talks About

Once you understand how the hemispheres connect to movement, the next step is learning to read the body’s most obvious — and often ignored — cues: posture, gait, and asymmetrical tone.

That’s where the PMRF starts revealing itself.

We’ve all seen it: the shoulder that always rounds forward. The hip that won’t stabilize. The ankle that turns out.

But the nervous system leaves breadcrumbs if you know how to look:

• One shoulder is internally rotated, even at rest

• A hip that drops or a knee that caves in during gait or load

• The client constantly shifts off one side during squats or lunges

• Chronic pain or repeated injuries are always on the same side

• Slumped posture or poor tone only on one side

These aren’t strength issues. These are not just a glute not firing. Or bad posture. Or a tight hip flexor.

They’re neurological imbalances.

And they often trace back to a specific part of the brainstem: the PMRF — the pontomedullary reticular formation.

The PMRF governs automatic postural control and tone on the same side of the body.

When it’s underperforming, it stops sending sufficient signals to the extensors of that side.

The result?

The shoulder rolls in.

The trunk collapses.

The foot turns out.

And the brain begins to offload stability to the opposite side to feel safe.

"When the PMRF isn’t working on the left, the left foot turns out, the shoulder collapses, and the brain offloads weight to the right. It’s predictable. And trainable." – Matt Bush

So when you see that one-sided slouch, that chronic shift, that stubborn posture imbalance — you’re likely seeing a brainstem issue, not just a movement habit.

And the moment you start assessing from that lens, things start to change. Fast.

Clue 3: Bilateral Training Might Be Making the Problem Worse

Now that we’ve looked at posture patterns, let’s talk about what might be unknowingly reinforcing them.

Many of us use bilateral lifts to “even out” imbalances — but in a neurologically compromised system, that can backfire.

Here’s the hard truth: when you give a bilateral exercise to a client with a one-sided neurological deficit, the strong side dominates. The weak side just goes along for the ride.

You’re reinforcing the pattern. Not correcting it.

That’s why one-sided neurology requires one-sided input.

Stimulus on the weak hemisphere.

Activation of that region’s control of the body.

And this doesn’t mean single-arm rows.

We’re talking about brain-based drills that target the underperforming PMRF or cerebellum directly.

Clue 4: The Brain Responds to Specific, Targeted Input

So if bilateral exercises won’t fix the imbalance… what will?

This is where applied neurology shines.

Let’s look at how targeted sensory drills can help bring the under active hemisphere back online — often in seconds.

Once you’ve identified the under active side (via gait, posture, or strength asymmetry), you can start feeding the brain stimulus to that region.

Examples from NLN’s applied neurology system:

To target the PMRF:

• Bounce gently with the head neutral or tilted toward the affected side
• Smell a strong scent through the nostril on that side
• Bite or apply tactile input to the cheek on that side
• Load from shoulder to opposite hip with a band or light weight

To activate the cerebellum:

• Perform hip circles or hand figure-eights on that side
• Do same-side saccades (quick eye movements)
• Combine breathing + movement to bring that hemisphere online

Then retest the client’s posture, strength, or gait. Often, you’ll see changes within seconds. 

You can learn about our NLN Assessment and Reassess process in our FREE masterclass.

“It’s not magic. It’s the nervous system responding to safety. When the brain feels safe, it allows strength.” – Matt Bush

Clue 5: Real Case — The Right Side That Just Wouldn’t Fire

To make this real, let’s show you how all of this comes together in practice.

Meet Chris — a client whose right side wouldn’t cooperate until we addressed the real issue: his brain.

Chris came in with chronic right knee pain.

Every lunge, squat, and single-leg stance showed a clear collapse on the right.

Trainers had tried strength work, mobility, glute activation. Posture, mobility, and foam rolling, the whole 100 yards of biomechanical educational tools. 

Nothing held.

We watched his gait.

Right shoulder rolled forward.

Right foot turned out.

Right arm swung excessively.

PMRF on the right was likely not firing.

We tested with:

• Right-side bounce drill
• Strong smell through the right nostril
• Tongue to left cheek (cross input to target right brainstem)

After just one round, his posture was noticeably more upright.

His single-leg stance improved. More importantly, he said, "That side actually feels alive now."

And for the first time in months, his split squat didn’t collapse.

To see more examples, watch this free masterclass.

This is what applied neurology offers: a way to target the root, not just the symptom.

Clue 6: The Industry Wasn’t Wrong — But the Brain Adds the Missing Context

Now that you’ve seen a real-life example, let’s zoom out.

Why haven’t we been trained to see movement this way before?

The answer lies in how the industry evolved — and why neuroscience is changing everything.

To be clear: the strength and rehab world isn’t wrong.

In fact, the industry has noticed that unilateral strength training matters.

We’ve been told to train one leg at a time.

Address imbalances.

Build core strength to support asymmetries.

And we should.

That perspective is valid — because it came from the best education we had available at the time.

But that education was built on a biomechanical model.

One that prioritized muscles, joints, and structure.

And while those matter, we now know something even more fundamental: the nervous system governs everything.

Recent neuroscience has made it clear — motor output is not just about load and reps.

It’s about input and safety.

The brain determines whether or not to allow full expression of strength.

It modulates tension, balance, timing, and coordination — often asymmetrically.

And here’s what’s wild:

Studies like those by Carroll et al. (2006) and Farthing et al. (2009) demonstrate that even unilateral strength training can produce cross-education effects — strength gains in the untrained limb — via cortical and spinal adaptations.

That means we’ve already seen the nervous system at work. We just didn’t have a name for it.

But now we do: applied neurology.

And at Next Level Neuro, our goal isn’t to dismiss biomechanics — it’s to add context.

To expand the model.

To help you see why sometimes, no matter how much you strengthen a limb, the deficit doesn’t budge… because the real weakness lives in the brain’s output to that limb.

“We don’t want you to abandon strength work. We want to give you tools to finally make it stick.” – Kathy Mauck, co-founder NLN.

This isn’t about replacing what you know. It’s about upgrading it.

Let’s show you how.

Clue 7: Assessing the Brain Isn’t Optional — It’s the Upgrade

So what does this mean for you, practically?

If you're coaching movement, you’re already working with the brain.

The next step is learning how to assess and train it — directly, intentionally, and effectively.

If you're coaching movement, you're already coaching the nervous system.

But without understanding which side of the brain might be underperforming, you’re missing critical information.

This doesn't mean you need to become a neuroanatomy expert. But it does mean you can:

• Use posture and gait as simple assessments
• Spot the asymmetry patterns that point to cerebellar or brainstem issues
• Choose drills that actually activate the correct side
• Build smarter warm-ups and correctives that stick longer with a brain first perspective. 

It’s not about doing more. It’s about doing what works — because it’s targeting the actual driver of dysfunction.

Want to Learn How to Do This?

Start With Our Fundamentals Course self-teaching course.  Read More here.

If you’re nodding along, but wondering how to actually start applying this, we’ve got you covered in this Fundamentals Course

1. The Fundamentals Of Neurology Course

Our self-paced, video-based training gives you the core concepts:

• What parts of the brain control movement
• How to assess clients simply, without equipment
• Drills for cerebellum, PMRF, and motor cortex
  

It’s where most coaches, therapists, and movement pros begin.

You can start using it tomorrow.

2. The NLN Mentorship Program

This is our hands-on, high-touch deep dive into applied neurology: (you do NOT need a neuroscience degree) 

• 12 months of support
• Real-time client case reviews
• Live weekly education calls.
• Access to a network of top movement professionals
• In-person Live events to learn and apply the education.

If you want to master this system — not just dabble — this is for you.

Next Cohort starts June 2025. 

“The mentorship changed how I see the body. It gave me answers I never got in therapy school.” – Louie, graduate.

The Side That Keeps Breaking Might Just Need to Be Heard

One-sided breakdowns aren’t a mystery.

They’re a message.

A message from the nervous system saying, “I’m not okay over here.”

You can listen.

You can test.

And you can start giving the brain the input it needs.

When you do, your clients will move better, feel better, and finally understand what it means to be in balance — from the inside out, from a brain first perspective. 

Ready to start? Choose your next step:

• Begin the self-paced Fundamentals of Neurology Course
• Explore the full NLN Mentorship
• Or get on a call with us to discuss the mentorship and education options— we’ll help you decide

Because when you train the brain, you don’t just build strength. You build resilience.