My Runs - Stop Guessing Your Endurance Limit: Introducing Aerobic Decoupling Analysis

Stop Guessing Your Endurance Limit: Introducing Aerobic Decoupling Analysis

Last updated: November 7, 2025

We've all had that run where the first 30 minutes felt effortless, but then the next 15 minutes felt like running through sand. You look at your data and see you slowed down, but the critical question remains: When exactly did my effort stop being efficient?

For runners focused on Zone 2 training and building true endurance (the core philosophy of My Runs), finding that physiological breaking point—the moment your heart started working too hard for the pace you were holding—has always been a guessing game. No more.

We are incredibly excited to introduce the Aerobic Decoupling Analysis, a powerful new feature that takes the guesswork out of endurance and finally gives you a precise, objective measure of your true Time to Fatigue (TTF).

The Problem: Heart Rate Drift Hides Your Limit

You might think if your pace stays consistent, your endurance is fine. But that ignores Cardiac Drift: as your run goes on, your heart rate (HR) naturally rises to sustain the same pace, even if you feel okay.

If your pace is 5' /km at the start using 140 BPM, but at the end, it takes 147 BPM to hold 5' /km, your efficiency has dropped. You are "decoupling."
The question is not if you decoupled, but when and how fast it happened.

The Fix: Efficiency Ratio and The Official Boundary

We solved this mystery by focusing on the Pace/HR Efficiency Ratio. This ratio tells the complete story of your run's quality, minute by minute.

Chart Line: The Blue Efficiency Trend

The main, thick blue line shows your Pace/HR ratio decay. When the blue line starts to drop, your effort is beginning to cost too much. It’s the visual history of your fatigue.

The Red Threshold Lines: Unmistakable Failure

We needed a clear, undeniable line to define failure. Scientific consensus holds that a drop of 5% or more from your initial baseline efficiency is the point where aerobic fatigue is confirmed.

Horizontal Red Line (Threshold Value): This is the 5% drop-off line. If your blue efficiency trend line falls below this red horizontal line, decoupling is officially triggered.
Vertical Red Line (Threshold Timestamp): This is the most important marker! It defines the exact Time to Fatigue (TTF). This line points to the duration you sustained your maximum aerobic output before fatigue was confirmed.

When you look at the chart, the longer that red vertical line is pushed to the right, the better your endurance and the more successful your Zone 2 training has been.

What Your Threshold Pace Tells You About Your Training

The analysis doesn't just stop at time; it gives you an actionable pace metric: the Threshold Pace.

The algorithm looks at the pace you were holding during the segment just before the red vertical line appears. That pace is your sustainable Aerobic Threshold Pace.

Insight: This is the highest pace you can hold where your body is still using oxygen highly efficiently. You can use this pace as the upper boundary for your Zone 2 runs going forward, ensuring you don't overshoot your effort and revert to inefficient running.

The Full Story: Max Efficiency

To complete the picture, we added the Max Efficiency Timestamp (Yellow Dashed Line):

This yellow line marks the peak efficiency achieved during your run. Ideally, this should happen quickly, confirming you hit your sustainable pace zone right after your warm-up.
If the yellow line appears late—say, 25 minutes into a 45-minute run—it means your body took too long to stabilize. It’s a powerful hint that your warm-up routine needs to be faster or longer.

We built My Runs to give you the clean, honest data you need to be a better version of yourself. This new decoupling feature is the ultimate tool for monitoring progress in endurance and consistency. Dive into your run data and find out exactly when your limit was met!