Run Smarter with Science
Free, evidence-based tools for training paces, race predictions, lactate thresholds, polarized training plans, and race-day nutrition — powered by peer-reviewed research.
Built by Runners, for Runners
Built on Science, Not Guesswork
Twelve specialized tools organized into three science-backed categories — from race prediction to threshold training to physiological analysis.
VDOT (Daniels)
Structured training plans
Well-researched, widely used by coaches
±3–5% for trained runners
Riegel
Quick race predictions
Simple, intuitive, single-race input
±5–8% across distances
Critical Speed
Endurance-focused athletes
Captures individual fatigue profile
±3–6% with good inputs
Lactate Threshold
Threshold-based training zones
Physiologically-grounded zone boundaries
LT1 & LT2 from race data
Polarized 80/20
Elite training distribution
Research-proven for long-term adaptation
Based on Seiler (2006) research
VO₂max
Gold-standard fitness metric
Universally accepted physiological benchmark
Estimated from race pace via Cooper & Daniels
The Science Behind Your Paces
Every calculation is grounded in peer-reviewed exercise physiology research — from classic race prediction to modern threshold-based training.
Daniels & Gilbert (1979)
Oxygen Power
Established the VDOT tables mapping VO₂max to optimal training paces — the foundation of modern distance-running coaching used by Olympic athletes worldwide.
Riegel (1981)
Athletic Records and Human Endurance
Derived the power-law formula T₂ = T₁ × (D₂/D₁)^1.06 that predicts race times across distances with remarkable accuracy, published in American Scientist.
Jones & Vanhatalo (2017)
The Critical Speed Concept
Validated the two-parameter Critical Speed model (CS + D') as a superior predictor of endurance performance, published in Sports Medicine.
Seiler & Kjerland (2006)
Quantifying Training Intensity Distribution
Demonstrated that elite endurance athletes follow an 80/20 polarized training distribution — ~80% easy, ~20% high-intensity — producing superior adaptations compared to threshold-heavy approaches.
Faude et al. (2009)
Lactate Threshold Concepts
Comprehensive review establishing LT1 and LT2 as the two key metabolic boundaries for endurance training prescription — the physiological basis for modern threshold-based training zones.
Ely et al. (2007)
Impact of Weather on Marathon Performance
Analyzed 1.8 million marathon results and found performance declines 1–3% for every 5 °C above the 5–10 °C optimum — the basis of our heat adjustment model.
Every Tool a Runner Needs
From training paces to race-day fueling — built by runners, backed by research.
See It In Action
Real calculator outputs — powered by peer-reviewed models, free for every runner.
What the Research Shows
Insights from the scientists whose work powers our calculators.
“Runners who train at the appropriate intensities — not too fast, not too slow — improve their VO₂max more efficiently than those who train by feel alone.”
Jack Daniels, Daniels' Running Formula (3rd ed., 2013)
On why VDOT-based training zones outperform guesswork
“The intensity distribution of successful endurance athletes is characterized by a large volume of low-intensity training, combined with a smaller proportion of high-intensity training.”
Stephen Seiler, International Journal of Sports Physiology and Performance (2010)
The research behind the 80/20 polarized training model
“The critical power concept provides a rigorous, physiologically-based framework for predicting performance across a range of endurance exercise durations.”
Jones & Vanhatalo, Sports Medicine (2017)
Why Critical Speed is the gold standard for multi-distance prediction
Built for Every Runner
Whether you're lacing up for your first 5K or chasing a sub-3 marathon, we have the tools.
Marathon First-Timer
Use the Training Pace Calculator for safe zones, the Carb Fuel Calculator for race-day nutrition, and the Lactate Threshold Calculator to understand your aerobic limits.
→ Training Pace CalculatorCompetitive Racer
Leverage the Race Predictor with the Hybrid model, dial in your LT1/LT2 paces with the Lactate Threshold tool, and build structured sessions with the Double Threshold Planner.
→ Race Time PredictorScience-Driven Athlete
Explore your lactate curve with the Lactate Simulator, structure 80/20 splits with the Polarized Training Calculator, and estimate your VO₂max from race results.
→ Lactate SimulatorRunning Coach
Access all 12 calculators to build individualized plans — from threshold-based zones to heat adjustments to nutrition targets for athletes of every level.
→ All 12 ToolsFrequently Asked Questions
Got questions? We've got answers backed by research.
Ready to Run Smarter?
Join thousands of runners using science-backed tools to optimize their training.