Have you ever been told that different energy systems take over at different times during a workout or game? Or that training your aerobic system will make you slow? Or that training must mimic your sport movements to be effective?

These ideas are common—but they’re wrong. And believing them can hold you back as an athlete or coach.

Let’s clear the air and dig into how energy systems really work. Because once you understand the truth, you’ll be able to build training plans that are more effective, more efficient, and more science-based.

Myth #1: Energy Systems Are Duration-Specific and Work Separately

This is one of the most widespread misunderstandings in the world of sport science. You’ve probably seen this image—or something like it—in a textbook or course:

This model implies that energy systems take turns. The ATP-PCr system dominates during very short efforts (like a 5-second sprint), glycolytic takes over for intermediate durations, and the aerobic system only shows up when you’re deep into a long run.

It’s a simple visual. And it’s dead wrong.

The truth is that all energy systems contribute simultaneously, from the very first moment of activity. Even during extremely short efforts, the aerobic system kicks in much faster than previously believed.

The idea of clean handoffs between energy systems is outdated. Modern studies show that aerobic metabolism can begin supporting ATP resynthesis in under 150 milliseconds after the start of activity.

That’s faster than most people blink.

So what does this mean for training? It means even “anaerobic” work involves aerobic processes. And even long steady-state training still stresses fast ATP turnover early in the effort. Training one energy system in isolation isn’t just difficult—it’s nearly impossible.

That’s why it’s essential to stop thinking of energy systems as separate lanes. Instead, think of them as overlapping contributors that scale up or down based on demand.

Your PCr system provides explosive power quickly but depletes rapidly. Meanwhile, your aerobic system is always humming in the background, helping to restore that PCr—even during maximal efforts.

As you can see above, phosphocreatine (PCr) recovery after maximal effort is directly dependent on oxygen availability. That’s aerobic metabolism in action—even in explosive sports.

So rather than isolating your energy systems, the real goal of training should be improving their integration and interplay.

Myth #2: Aerobic Training Kills Your Speed and Power

This one comes from a kernel of truth—but it’s been distorted over time.

Yes, doing excessive low-intensity work without any speed or power training can dull your explosiveness. But that doesn’t mean aerobic training itself is bad.

In fact, for most field and court athletes, a well-developed aerobic system is one of the best tools you can have to support speed and power.

Let’s take soccer as an example.

Repeated sprint ability (RSA) is one of the most important physical qualities in football. Athletes need to accelerate, recover, and go again—over and over.

You don’t just need a strong first sprint—you need to hold your performance over time. And that’s where energy systems come in.

Research shows that aerobic fitness significantly predicts RSA performance. One study found a correlation of R² = 0.89 between OBLA (onset of blood lactate accumulation or Threshold 2) and RSA. That’s a huge effect.

Here’s why it matters: after a sprint, your muscles rely on oxidative metabolism to clear lactate, resynthesize phosphocreatine, and restore pH balance. If your aerobic system is weak, you recover slower. That means your next sprint is worse—and so is the one after that.

This directly connects aerobic capacity to repeated power output.

Even better: we now know that fast-twitch muscle fibers have mitochondria too. They’re not just raw, explosive units. They contain oxidative machinery specifically tuned for high power output.

Fast-twitch mitochondria may not be the most efficient, but they’re optimized for rapid ATP production—exactly what you want during heavy sprint-based efforts. So aerobic training doesn’t kill power. It builds the foundation for repeating it.

Your energy systems aren’t fighting each other—they’re cooperating.

Myth #3: Training Must Always Look Like Your Sport

This is the “train like you play” fallacy. It sounds logical on the surface—why not just mimic the demands of your sport in training?

But trying to replicate sport intensity and movements all year long leads to one thing: stagnation. You never address weaknesses or build the systems that support peak output.

Instead, the goal should be to train all energy systems, throughout all intensities, at different points in the season. That’s how you build a complete athlete.

Training needs to address:

• Low-intensity aerobic base (capillary density, fat oxidation)
• Mid-intensity threshold work (lactate buffering, oxidative capacity)
• High-intensity glycolytic power (glycogen usage, improved VO2max)
• Very high-intensity explosive work (neuromuscular output)

If all you ever do is simulate sport-specific movement, you neglect parts of the energy systems spectrum that allow you to go harder, longer, or recover faster.

So What Should You Actually Do?

Let’s keep it simple. Here’s how to build your energy systems with purpose:

1. Train all endurance qualities year-round. Don’t neglect any zone—each one supports a different function.
2. Focus on general capacity away from competition. Use this phase to build your aerobic base and tissue tolerance.
3. Target specific energy systems as competition nears. Fine-tune the qualities you need on game day.
4. Do the training you haven’t done. Novel stimuli drive adaptation.

This is not about random variety—it’s structured diversity across the energy spectrum.

Final Thoughts: Integrate, Don’t Isolate, Your Energy Systems

The biggest takeaway? Energy systems don’t operate in silos. They work together, respond together, and adapt together.

Every athlete—whether you sprint, jump, cut, or grind out long races—relies on the integrated function of these systems. And your training should reflect that.

Forget the myths. And instead of focusing on energy systems, think about intensity domains (or “levels”).

Because once you understand how to train those, you unlock the next level of your performance.