The Riegel formula, developed by Pete Riegel in 1977, predicts a runner’s time at one distance from a known time at another: T2 = T1 × (D2/D1)^1.06. The 1.06 exponent accounts for the non-linear energy cost of running longer distances — each doubling of distance takes roughly 8% more time per kilometre than the previous. The formula is most accurate for trained runners who race regularly and least accurate for marathon prediction (where training specificity and glycogen availability introduce large individual variation).
Key points
- T2 = T1 × (D2/D1)^1.06
- 1.06 exponent accounts for endurance fatigue
- Accurate within 3-8% for trained runners
- Less accurate for marathon (glycogen wall)
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