Can I predict my marathon time accurately from a 5K test?

While mathematically possible, a 5K relies 85% on aerobic capacity and 15% on anaerobic power, whereas a marathon is 99% aerobic and limited by hepatic/muscular glycogen capacity. A Half Marathon time provides a much more accurate predictor for a Full Marathon.

What is negative split pacing in endurance racing?

A negative split occurs when the second half of a race is run faster than the first half. Physiological data confirms this is the optimal pacing strategy for distance records, preventing premature lactate accumulation and preserving muscle glycogen stores.

What cadence (steps per minute) should I aim for when running?

Most elite distance runners maintain a stride cadence between 170 and 185 steps per minute (SPM). Higher cadence reduces ground contact time, shortens over-striding, and significantly lowers peak impact forces on the patellofemoral joint.

Can I predict my marathon time accurately from a 5K test?

While mathematically possible, a 5K relies 85% on aerobic capacity and 15% on anaerobic power, whereas a marathon is 99% aerobic and limited by hepatic/muscular glycogen capacity. A Half Marathon time provides a much more accurate predictor for a Full Marathon.

What is negative split pacing in endurance racing?

A negative split occurs when the second half of a race is run faster than the first half. Physiological data confirms this is the optimal pacing strategy for distance records, preventing premature lactate accumulation and preserving muscle glycogen stores.

What cadence (steps per minute) should I aim for when running?

Most elite distance runners maintain a stride cadence between 170 and 185 steps per minute (SPM). Higher cadence reduces ground contact time, shortens over-striding, and significantly lowers peak impact forces on the patellofemoral joint.

Running Pace & Race Time Predictor

Name: Running Pace & Race Time Predictor
Author: ZenFit Tools

ZenFit Tools/performance/Running Pace & Race Time Predictor

4 min readEndurance Science

Running Pace & Race Time Predictor

Convert split paces (min/km & min/mile) and predict 5K, 10K, Half, and Full Marathon times using Pete Riegel’s fatigue equation.

Formula: Riegel Fatigue Model: T2 = T1 × (D2 / D1)^1.06

Input Parameters

Metric

Distance (Kilometers)

Hours

Minutes

Seconds

Instant Biometric Computation

Calculated Pace

4:51 /km

Speed: 12.4 km/h · Est. VO2 Max: 37.4 ml/kg/min

Pete Riegel Race Time Predictions

1 Mile6m 60s4:21 /km

5K23m 16s4:39 /km

10K48m 30s4:51 /km

Half Marathon1h 47m 1s5:04 /km

Marathon3h 43m 7s5:17 /km

Export to Fitness Logs & Spreadsheets

Save this calculation for your training log: Apple Notes, Notion, Obsidian, Google Sheets, or Excel.

Verified 100% Client-Side Computation

How This Calculator Works & Mathematical Formula

Pete Riegel Endurance Equation:

T2 = T1 × (D2 / D1)^1.06

Where T1 is your baseline race time, D1 is baseline distance, D2 is target distance, and 1.06 is the empirical fatigue exponent across human aerobic events from 1,500m to ultra-marathons.

Standard Physiological Guidelines & Scientific References

Clinical Society Guidelines

World Athletics Physiological Evaluation Models
Riegel PS. Athletic records and human endurance. American Scientist. 1981;69(3):285-290.
Daniels J. Daniels' Running Formula (4th Edition). Human Kinetics, 2021.

Peer-Reviewed Citations

Vickers AJ, Vertosick FT. An empirical study of race times in recreational marathon runners. BMC Sports Sci Med Rehabil. 2016;8:26.
Noakes TD. Lore of Running (4th Edition). Human Kinetics, 2003.

Important Planning Assumptions & Safety Disclosures

•The Riegel prediction assumes adequate aerobic base training for the target distance. Attempting a marathon based purely on 5K pace without high weekly mileage will result in glycogen depletion ("the wall").

•Environmental factors including heat index, humidity, elevation, and terrain grade alter pacing requirements by 3-15%.

Frequently Asked Questions (4 Technical Inquiries)

In 1981, research engineer Pete Riegel analyzed world records from 1,500m to 100 miles. He discovered that human speed decays at a predictable logarithmic power function with an exponent of 1.06 due to neuromuscular fatigue, glycogen depletion, and thermoregulatory load.

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