HOW WE CALCULATE RACE CONDITIONS

WBGT (Heat Stress)

Combines temperature, humidity, wind, and sun into one number. More accurate than "feels like" for exercise.

Pace Adjustment

Based on research showing ~0.35% slowdown per 1°C WBGT above 15°C (optimal range: 7.5-15°C).

Example: WBGT 25°C = +3.5% slower (~20 sec/mi for most runners)

Hydration Multiplier

Baseline: 400-800ml/hour. Add 8% per 1°C WBGT above 15°C. Add 5% per 10% humidity above 60%.

Example: Hot humid day (WBGT 25°C, 80% humidity) = 1.9x normal intake

Dew Point

Measures atmospheric moisture. <10°C = dry, 10-16°C = comfortable, 16-20°C = sticky, >20°C = oppressive.

Where We Get the Data

• Weather: Open-Meteo API (5 years of historical data for race date)
• Research: Ely et al. (2007), PMC8677617 (2021), Sawka et al. (2007), Liljegren et al. (2008)
• Races: Official race websites, manually verified

What to Know

• • Based on population averages — individual runners vary in heat tolerance
• • Historical data doesn't guarantee future weather (we use real-time forecasts when available)
• • WBGT is estimated (±2°C accuracy) without direct solar radiation measurement
• • Single-point weather data doesn't capture course microclimates (shade, elevation, wind)