TTF, NGP, ADS: How to Master Consistency and True Effort
Last updated: November 17, 2025
You’ve stopped guessing your endurance limit—that’s great. Now it's time to master your effort.
With the introduction of Grade-Adjusted Pace (NGP) and the powerful Aerobic Decoupling Analysis, your data now accounts for every hill and valley. But precision comes with nuance.
In a single run, you get three critical metrics that tell a complete story:
- Time to Fatigue (TTF): The exact moment your efficiency failed (the 5% drop).
- Sustainable NGP: The True Effort Pace you were holding just before the failure.
- Aerobic Decoupling Score (ADS): The total, overall degradation of your efficiency from start to finish (the magnitude).
These numbers don't always align, and understanding their conflicts is the key to becoming a smarter endurance runner. Here is your definitive guide to using all three metrics together across different training scenarios.
Scenario 1: The Gold Standard Run
Results
- TTF: Not captured (or TTF is equal to the Run Duration)
- ADS: Low (< 5%)
Interpretation: You Nailed It.
This is the goal for Zone 2 training. Your low ADS proves your efficiency degradation was minimal over the entire run. Your TTF shows you could sustain the effort for the full duration. This run perfectly balanced effort and duration.
Future Training Action
- Progression: This run validates your current training stimulus. It’s time for Progressive Overload next week. Increase either your NGP slightly (e.g., 10:00/mi to 9:55/mi) or increase the duration (e.g., 45 min to 50 min).
Scenario 2: The Transient Failure
Results
- TTF: Captured early (e.g., 10 min)
- ADS: Low (< 5%)
Interpretation: Systemic Success, Local Failure.
This is where the TTF and ADS conflict, and the conflict is highly actionable. Your low ADS means the run was successful overall (you recovered and stabilized), confirming the run was high-quality and beneficial. However, the early TTF is a flashing red light warning you about The Start.
Future Training Action
- Root Cause Analysis: Analyze the NGP you were holding in the moments just before the TTF. This NGP is your vulnerability. You started too hard, even if momentarily.
- Pacing Correction: For the following week, consciously start your runs at an NGP that is 10-15 seconds slower than your Sustainable NGP, focusing purely on effort for the first 10 minutes to ensure a slow, coupled start.
Scenario 3: The Systemic Breakdown
Results
- TTF: Captured early/mid-run (e.g., 20 min)
- ADS: High (≥ 10%)
Interpretation: Unsustainable Effort.
Both metrics confirm a substantial failure. The high ADS proves the inefficiency was sustained throughout the second half. The captured TTF simply marked the moment the body first signaled the effort was too much.
Future Training Action
- Reduce Effort: Your current Sustainable NGP is too fast for your current fitness level or fatigue status. Reduce your target NGP by at least 15-20 seconds per mile for your next run.
- Check External Stressors: This scenario demands you check environmental (heat/humidity) and systemic factors (sleep, stress, fatigue). A sudden run of high ADS scores suggests you may be overtraining or under-recovering.
Using Your Sustainable NGP as the Prescription
The Sustainable NGP captured just before your TTF is the most powerful number for your training plan.
If your TTF is consistently captured at 30 minutes at 9:45/mi, then 9:45/mi is your current aerobic ceiling for that duration.
Your Goal: Drive your TTF further and further into your run at that NGP. Once your TTF hits 45 minutes, you’ve earned the right to try a 9:40/mi NGP next time.
Stop letting averages and overall paces fool you. Use your TTF, ADS, and Sustainable NGP in combination, and start training with objective, precise data that reflects your true physiological progress!