Estimate target race finish times from a recent result using Peter Riegel's validated fatigue exponent equation.
A running coach evaluating a half marathon training cycle checks recent 5K race results to establish realistic target race paces. Setting marathon targets based only on wishes can lead to early energy depletion. Using a validated mathematical model provides a realistic target timeline.
Race time predictors estimate future performance over a target distance based on a recent race time. These estimates serve as valuable guides for structuring training paces and setting realistic goals on race day.
Published in 1977 by research engineer Peter Riegel, the formula has become the endurance standard for race time prediction. The formula models aerobic capacity decay over extended durations:
T2 = T1 × (D2 / D1)^1.06Where:
Riegel's formula assumes the runner has completed adequate training volume for the target distance. While a 20-minute 5K predicts a 3:10 marathon mathematically, achieving that time is only possible if the runner has built the necessary cardiovascular volume and muscular endurance. Without sufficient weekly volume, fatigue will exceed the standard 1.06 exponent, causing a slower finish time.
Predictions assume identical environmental and course conditions. Adjustments should be made for:
Calculations use client-side float exponentials. Distance ratios are converted to identical units (kilometers or miles) before division. Outputs display predicted times formatted into hours, minutes, and seconds, and include equivalent target paces.
No. The 1.06 fatigue exponent is calibrated specifically for aerobic events lasting between 3 minutes and 4 hours. Anaerobic sprints follow different fatiguing and energy pathways.
This is common for amateur runners. The marathon requires specific glycogen storage capacity and lipid oxidation efficiency. If training volume is insufficient to build these pathways, fatigue increases, resulting in a slower time than predicted from shorter distances.
No. Walking uses different biomechanics and muscle groups, which do not follow the same aerobic fatigue curve modeled by the 1.06 running exponent.
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