Concurrent Training: Why Your Gains Keep Disappearing

You spent three months getting stronger. Then you added cardio—and your strength faded.

Or you built your engine, then focused on strength—and your conditioning fell off a cliff.

As a fighter, you’re spinning a lot of plates. You can’t focus on all of them at once—that’s how plates get smashed.

You thought you were making progress. You were actually erasing it.

I’m Don Heatrick. After coaching over a thousand fighters through their strength and conditioning, I can tell you this pattern is almost universal—whether you’re preparing for a fight or just trying to become a better all-round athlete.

Fighters and practitioners work hard for months. They see real progress in one area—then watch it disappear the moment they shift focus to something else.

Or, they try to do everything at once—strength, power, speed, endurance—only to succeed at nothing. Other than draining energy and maybe getting injured.

Most blame genetics. Some blame age. A few blame themselves for not working hard enough.

But the real cause has a name. And once you understand it, you’ll see exactly why your training keeps resetting to zero—and why the improvements you make never seem to stick.

It’s called the Interference Effect.

And here’s what it means: when you train certain athletic qualities together—or in the wrong order—they don’t just fail to stack. They actively cancel each other out. You create conflicting adaptations that cause you to lose the results of all the previous work you’ve done.

Let me give you the most common example.

You spend a training block getting stronger. Your numbers go up. You feel more powerful in the gym. Then you think, “Time to build my engine,” and you pile on high-volume cardio.

A few weeks in, your strength numbers start slipping. A couple of months later, you’ve lost most of what you built.

You didn’t lose your strength because you stopped lifting. You lost it because the type of cardio you added—or the timing of that training—created a conflicting signal. Your body received two contradictory demands and had to choose.

The cardio won. Your strength gains got erased.

If you’re watching this thinking, “That’s exactly what happens to me”—you’re not alone.

I’ve built a free assessment that identifies exactly where your training might be creating interference instead of progress. Takes about five minutes. Link’s in the description.

Here’s what the Interference Effect looks like in practice. See if any of these describe you.

Pattern one: You feel stronger in the gym than you perform on the pads or in sparring.

You’ve built strength, but it doesn’t show up when you’re actually training. Some fighters tell me, “When I strength train, it hurts my sparring speed and reaction time.” That’s because the strength was never converted into sport-specific power and speed—and the way you trained cardio interfered with that conversion.

Pattern two: You start every year with the same goals.

Get stronger. Get faster. Improve your cardio. And every year, you end up roughly where you started. Not because you didn’t work—but because your training kept resetting itself. You lose your gains as soon as you switch focus.

Pattern three: You feel fitter mid-training block than you do when it matters most—whether that’s fight night, a grading, or just when you’re testing yourself in sparring.

You peaked too early. Or you trained qualities that faded before you could use them. The timing was wrong. If the improvements you make don’t last long enough to show up when it counts, it’s a waste of time and energy.

Pattern four: You’re either burned out or feeling like you’re not doing enough.

I hear this constantly: “I always get injured or burned out after weeks of training.” There’s no middle ground. You swing between overtraining and undertraining because you don’t have a system that tells you what’s actually required.

The Interference Effect explains all of these. It’s not four separate problems—it’s one problem showing up in different ways.

So why does this happen? Why do our bodies work against us like this?

Here’s the simple version: different training adaptations require different—sometimes opposite—signals.

Strength training tells your muscles to produce maximum force. It prioritizes the neural pathways that recruit the most muscle fibers possible for a single, heavy effort.

High-volume endurance training tells your body to get efficient at lower-intensity, sustained work. It prioritizes energy conservation and fatigue resistance over maximum force production.

When you send both signals at the same time—or in the wrong sequence—your body compromises. It doesn’t fully adapt to either. You get a watered-down version of both.

For a fighter or serious practitioner, that means you’re neither strong enough nor conditioned enough to dominate.You wasted time and effort without getting a return, and worse, put needless extra miles on the clock.

But here’s what most people miss completely: there’s a specific sequence for building athletic qualities. Each one sets the foundation for the next, and they stack on top of each other with a compounding effect.

You need to build functional strength first—the ability to generate maximal force using proper movement patterns. Then you convert that strength into power—training your muscle fibers to generate high force more quickly. Then you convert that power into speed—applying it to the fast movement patterns of your sport.

Build them out of order? You create conflicting adaptations. Build them in the wrong combination? You cancel out your gains.

The research calls this “concurrent training interference.” And it’s been studied extensively. The order you build qualities matters. The combination matters. The timing matters.

Get it wrong, and you’re not just wasting time—you’re actively undoing your previous work.

Here’s what makes this so frustrating: you can’t feel interference happening.

You show up. You train hard. You sweat. You might be sore the next day. Everything feels like it’s working.

But underneath the surface, your adaptations are fighting each other.

One fighter put it perfectly: “I struggle with knowing if my current program is optimal, or if I’m getting in shape by default just because I’m doing something rather than nothing.”

That’s the trap. You’re making progress—just not as much as you should be. And you have no way of knowing what you’re leaving on the table.

This is why so many people stay stuck for years. They’re not lazy. They’re not uncommitted. They’re working hard at a system that’s fundamentally broken—and they have no way of knowing.

Your measure of a good session shouldn’t be how hard it feels. The real question is: is it making you better, or just making you tired?

The Interference Effect is invisible until you understand what to look for. And once you see it, you can’t unsee it. You’ll recognize it everywhere—in your own training history, in the programs you’ve tried, in the advice you’ve been given.

Let me give you a real example of what happens when you get this right.

Daan came to me during lockdown. He’d been doing Stronglifts 5×5—a solid novice powerlifting program. Great for raw strength. Absolutely useless for cardio. His aerobic capacity was his biggest weakness, and he knew it.

Before starting, he did all the performance tests. Then he committed to twelve weeks of the Heavy Hitters program—following every session, skipping nothing.

Here’s what’s interesting: some of those sessions didn’t even feel like hard work. Thirty-minute cardiac output sessions he’d do while watching Netflix. But he trusted the system. He knew where he was heading.

Twelve weeks later, he retested. His Cooper run distance increased by eleven percent. His Wingate test results improved significantly. All his lifts went up—especially his weighted chin-ups.

But here’s the part that matters most: one minute after finishing the Cooper test, he felt ready to go again. That’s something he couldn’t have imagined before.

Daan didn’t work harder than he had before. He worked systematically. Each block built on the previous one. No conflicting adaptations. No reset to zero.

That’s what happens when you eliminate interference.

So what’s the answer? How do you train without creating interference?

The short version: there’s a specific sequence for building athletic qualities that avoids conflicting adaptations. Each quality builds on the one before it. Each training block develops one thing while maintaining everything else. And the whole system is timed so you peak exactly when you need to—not a week before, not a month after.

This is what separates people who progress year after year from those who keep resetting to zero.

I’ll break down that sequence in detail in upcoming videos.

But for now, the most important thing is recognizing the pattern.

If your training keeps resetting to zero, it’s not because you’re not working hard enough. It’s because the structure of your training is creating interference.

And that’s a solvable problem.

If you want to find out whether your current training is building progress or creating interference, I’ve put together a free assessment that breaks down exactly where you stand.

It takes about five minutes, and you’ll get a clear picture of what’s working and what’s holding you back.

Link’s in the description below.

Next week, I’m breaking down the four specific training traps that guarantee you never progress—and how to recognize which ones you’re falling into. Make sure you’re subscribed so you don’t miss it. And watch this video next.