How PACEFLOW Works
Learn the science behind personalized half-marathon training plans built on Jack Daniels VDOT formula
What is VDOT?
VDOT stands for VO₂max-equivalent. It's a metric created by legendary running coach Jack Daniels that quantifies your aerobic fitness level in terms of your VO₂max capacity.
Unlike heart rate or pace, VDOT is a stable, reproducible measure of your fitness that can be calculated from recent race performance. A runner with VDOT 50 is significantly fitter than one with VDOT 40, and VDOT directly determines the paces for every training zone.
💡 Why VDOT matters:
- ✓ Science-backed: Used by thousands of coaches worldwide
- ✓ Personalized: Based on YOUR fitness, not generic percentages
- ✓ Accurate: Proven to within 30-90 seconds of actual race performance
- ✓ Adjustable: Can be updated when you run a new race
How VDOT is Calculated
PACEFLOW calculates your VDOT in two ways:
From a Race Result (Most Accurate)
Provide a recent 5K, 10K, or half-marathon time. PACEFLOW uses Jack Daniels' formula to calculate your exact VDOT.
Pro tip: Within 6 months is ideal for accuracy
From Your Age (Estimated)
No recent race? PACEFLOW estimates VDOT based on your age and training experience. This is a solid starting point.
Pro tip: Calibrate in weeks 2-3 by running and adjusting if needed
The 5 Training Zones
PACEFLOW calculates exact pace and heart rate for each training zone. Each serves a specific purpose:
Zone 1: Recovery/Easy
Builds aerobic base, flushes lactate, allows adaptation
59-74% of VDOT pace
Zone 2: Marathon Pace
Trains at goal half-marathon pace, builds lactate threshold
84-88% of VDOT pace
Zone 3: Threshold/Tempo
Pushes lactate threshold, improves sustained effort
88-92% of VDOT pace
Zone 4: VO₂Max
Improves aerobic capacity and VO₂max
100-110% of VDOT pace
Zone 5: Anaerobic
Builds speed and power, used sparingly
110%+ of VDOT pace
Why VDOT Beats Percentage Methods
Many training plans use "run at 70% of max HR" or "60% of threshold pace." These methods work but are crude approximations. VDOT is more precise:
| Method | Accuracy | Personalization | Drawback |
|---|---|---|---|
| % of Max HR | ⭐⭐ | ⭐ | Max HR varies wildly; doesn't account for fitness |
| % of Threshold Pace | ⭐⭐⭐ | ⭐⭐ | Ignores VO₂max; one-dimensional |
| VDOT (Jack Daniels) | ⭐⭐⭐⭐⭐ | ⭐⭐⭐⭐⭐ | None — gold standard in coaching |
Note: VDOT accuracy depends on having recent race data or providing your real max HR / lactate threshold HR for calibration.
PACEFLOW vs Competitors
How does PACEFLOW compare to other popular running tools?
| Tool | Price | Science | Full Plans | Flexibility |
|---|---|---|---|---|
| McMillan Calculator | Free | ⭐⭐⭐⭐ | ❌ Predictions only | Low |
| Runna | €10-20/mo | ⭐⭐⭐ | ✓ Yes | ⭐ |
| Strava Plans | Free | ⭐⭐ | ✓ Generic | ⭐⭐ |
| TrainingPeaks | €10-30/mo | ⭐⭐⭐⭐⭐ | ✓ Advanced | ⭐⭐⭐⭐ |
| PACEFLOW | €9.99 one-time | ⭐⭐⭐⭐⭐ | ✓ Personalized | ⭐⭐⭐⭐ |
🏆 PACEFLOW Advantages:
- ✓ Jack Daniels science — Most proven coaching method available
- ✓ €9.99 forever — No subscription, no price increases
- ✓ Instant generation — 30 seconds from form to plan
- ✓ Flexible scheduling — Adapt to your busy days
- ✓ 30-day guarantee — Full refund if unsatisfied
Frequently Asked Questions
▶What if I don't have a recent race time?
No problem! PACEFLOW estimates VDOT based on your age. In your first 2-3 weeks, adjust paces based on feel. Everyone responds differently to training.
▶How accurate is the race prediction?
VDOT predictions are typically within 30-90 seconds of actual performance if you follow the plan at 90%+ compliance and taper properly. Real-world variables (sleep, nutrition, weather, pacing strategy) also matter.
▶Can I run faster or slower than the recommended paces?
Absolutely. The paces are targets, not rules. If easy feels hard, slow down. If marathon pace feels easy, speed up. Training should feel sustainable.
▶What happens if I miss a workout?
Skip it and resume the next day. Don't double up or panic. Your body adapts to training stress over time, not from individual workouts.
▶Can I change the number of runs per week?
Not within PACEFLOW (the plan is fixed to your choice), but you can skip runs or add extra easy days as needed. The important part is the hard workouts.
▶How do I know if my max HR is accurate?
Max HR can vary 10-20 bpm day-to-day. If you don't know it, leave it blank and use age-based estimation. It's only a reference anyway.
▶What's a "lactate threshold HR"?
It's the heart rate at which lactate accumulates faster than your body can clear it. It's roughly 85-90% of max HR. If you don't know it, we'll estimate it.
▶Should I follow a recovery week?
Yes! Every 4th week in PACEFLOW is automatically a recovery week (80% volume, reduced intensity). Recovery weeks prevent overtraining and boost adaptation.
▶Can I use PACEFLOW if I'm already trained?
Yes! PACEFLOW scales from beginner to elite. Competitive runners benefit most from providing a recent race time for accurate VDOT.
▶Is PACEFLOW suitable for my first half-marathon?
Absolutely. Beginner plans start with more base-building weeks and lower volume. Just provide your age and desired training length.
Ready to start your training?
Get your personalized half-marathon plan built on Jack Daniels VDOT formula. Free preview, €9.99 full plan.
Generate Your Plan →