Pre-Race Fitness Assessment: How to Predict Your PB Using Practice Races and Simulation Runs

Introduction

The pre-race mental drama is familiar to almost every Taiwanese runner: you sign up for the Taipei Marathon with a Sub-4 goal, but a week before the start you begin to doubt yourself: “Is my current training condition really good enough to break four hours? Or should I change it to 4:10?”

Setting a goal that isn’t challenging enough makes the race feel dull; setting a goal that’s too optimistic means the pain of a late-race collapse will make you hate yourself.

This article introduces several reliable pre-race condition assessment methods to help you make the most accurate PB prediction before race day, giving your goal-setting a solid foundation.

Method 1: Race Time Conversion Formulas Across Distances

The most commonly used PB prediction tool is converting a “known race result” into a “predicted result for the target distance.”

Common conversion formula (Riegel formula):

T₂ = T₁ × (D₂/D₁)^1.06

Important Limitation: This formula assumes the runner has sufficient aerobic endurance. If long-run training is insufficient (e.g., your longest run is only 20km), the latter half of a full marathon will deviate significantly from the prediction due to lack of endurance. Training completeness is a prerequisite for the accuracy of conversion formulas.

Method 2: Condition Assessment via Practice Races

Three to five weeks before your target marathon, find a 10km or half marathon practice race to use as a condition assessment tool.

How to interpret practice race results:

• Run it all out—don’t hold back—so the numbers are meaningful
• Observe whether you fade in the second half—if the second 5km is more than 2 minutes slower than the first 5km, your aerobic endurance or pacing strategy needs adjustment
• If you feel “just about” spent after the practice race, your training condition is good; if you feel “still quite fresh,” it means your pacing was conservative that day, and you can adjust your prediction upward

Taiwan-specific advice: The ideal practice race before the Taipei Marathon is a 10km event around October (such as small-to-medium road races at the start of the national season). Avoid overtraining before the practice race, or the result will underestimate your actual condition.

Method 3: Direct Assessment via Goal-Pace Simulation Runs

Two to three weeks before the race, schedule one “goal-pace simulation run”:

• For marathon preparation: Run 16–20km continuously at goal pace
• For half marathon preparation: Run 10–12km continuously at goal pace
• Evaluation criteria:
  • Is your rating of perceived exertion (RPE) after the run within 7–7.5 (on a 10-point scale)?
  • Is your heart rate maintained at 80–87% of maximum heart rate?
  • Can you complete the full distance at the same pace without significant pace drop-off?

If all three points hold true, the goal pace is feasible. If your heart rate has already spiked above 88% during the simulation run, it’s recommended to ease your goal pace by 5–10 seconds.

Method 4: Integrated Physiological Indicator Assessment

Beyond performance numbers, the following physiological indicators can also reflect pre-race condition:

Mental Adjustment During the Taper

During the 2–3 week taper before the race, many runners experience “Taper Madness”—legs feel heavy due to reduced weekly mileage, anxiety rises, and you doubt that you’ve regressed. This is a normal physiological and psychological phenomenon:

• Your legs are refilling glycogen and may feel slightly heavy—this is a good thing
• Mild discomfort during the taper does not mean your fitness has declined
• Two to three days before the race, your fitness typically peaks

Practical Advice

• Don’t make major decisions in the final week: The week before the race is for consolidating confidence, not for revising goals. Your goal should be finalized two weeks before race day
• Prepare two pacing plans, A and B: Plan A is the ideal goal (challenging), Plan B is the conservative goal (steady completion). After the race starts, decide which plan to execute based on how you feel in the first 5km
• Taiwan-specific information: Historical finish time distributions for major road races are usually available on race organizer websites or runner Facebook communities—you can reference results from runners of similar ability as a comparison

Conclusion

Accurate pre-race condition assessment is the prerequisite for setting a reasonable PB goal. It prevents you from wasting your potential by being too conservative, and from collapsing in the latter stages by being too optimistic. Through practice race conversions, goal-pace simulation runs, and integrated physiological indicators, you can stand at the starting line with clear confidence, knowing exactly how fast you can run today—and that certainty itself is half the PB.

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