The Conundrum That Sparked a Deep Dive

You lace up, track your training, put in the klicks or miles, and check your devices hoping for some feedback. And then you see it: your Garmin race predictor says you could run a sub-2 hour half marathon, while Strava suggests you’ll be closer to 2:20.
So who’s right? Or are they both wrong?
I asked AI for its predictions, using values collected from my Training Peaks metrics.
📊 Side-by-Side: Garmin vs Strava
Let’s look at what each platform predicted for me (July 2025):
Strava Predictions:
- 5K: 28:25 (5:41/km)
- 10K: 1:00:11 (6:01/km)
- Half: 2:20:37 (6:40/km)
- Full: 5:22:24 (7:38/km)

Garmin Predictions:
- 5K: 25:55 (5:11/km)
- 10K: 53:47 (5:22/km)
- Half: 1:59:15 (5:39/km)
- Full: 4:06:43 (5:51/km)

🧠 Why Are They So Different?
📊 Strava: Reality-Based, But Conservative
Strava predicts race times using your recent pace, grade-adjusted pace (GAP), and training load. It tends to underestimate performance unless you’ve logged races or hard efforts.
🧬 Garmin: Physiological Potential
Garmin’s estimates rely on VO2 max, heart rate, and training load, which means it often assumes you’ll race in ideal conditions. If you wear a chest strap regularly (I do), Garmin’s numbers get even bolder.
Summary:
- Garmin = Best-case scenario
- Strava = What your workouts suggest today
But neither gives a complete picture.
🏋️♂️ Enter: The Plus50Fit Predictor
Here is what AI prediction model using my actual TrainingPeaks metrics:
- rTSS (Run Training Stress Score)
- IF (Intensity Factor)
- Pa:HR (decoupling)
- RPE (perceived effort)
- Long-run endurance trends
Here’s what my model says as of July 3, 2025:
Distance | Plus50Fit Predicted Time | Avg Pace |
5K | 27:30 | 5:30/km |
10K | 58:00 | 5:48/km |
Half | 2:12:00 | 6:16/km |
Full | 4:48:00 | 6:50/km |
These estimates reflect actual effort, aerobic durability, and training stage (currently in Base Phase 2, Week 3). They sit comfortably between the extremes of Garmin and Strava.
🔄 Visualizing the Differences

- Strava flattens expectations.
- Garmin overreaches.
- Plus50Fit meets you where your legs and lungs actually are.
📊 What My Numbers Have Saying
- Pa:HR under 5% on long runs = strong aerobic base
- IF near 0.90 on threshold work = tempo readiness
- RPE self-assessment matches metrics = high training accuracy
- Training volume rising gradually = sustainable buildup
Translation: Building smart, and the Plus50Fit numbers will sharpen monthly.
✅ So Which Prediction Should I Trust?
Use Case | Trust This Predictor |
Everyday training | Strava |
VO2 trend check | Garmin |
Race goal setting | Plus50Fit Predictor (Yup!) |
🌟 Final Thoughts
Neither Garmin nor Strava is wrong—they’re just answering different questions.
- Garmin says: “Here’s what you might do at your absolute best.”
- Strava says: “Here’s what your workouts show today.”
- Plus50Fit says: “Here’s what your heart, legs, and lungs are actually capable of right now.”
Ready to find out which one wins on race day? I’ll keep updating this model as training continues.
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