The Numbers Game

VO2max — maximum oxygen uptake — is the single best predictor of endurance performance. It measures how efficiently your body uses oxygen at peak effort. Elite marathoners hover around 70-85 ml/kg/min. Recreational runners typically land between 35-50. I estimate yours from your personal bests using the Jack Daniels VDOT formula. Run a 5K in 25 minutes? That maps to a VDOT of roughly 38. Run it in 20 minutes? That's about 49. The math involves velocity-based oxygen cost curves and exponential decay functions for effort percentage at different durations. It sounds complicated because it is. But the input is simple: your best race time at a known distance.

Here's the magic trick: if I know your 5K time, I can predict your 10K, half marathon, and marathon times. The formula is Riegel's model: predicted time = known time * (new distance / known distance) ^ 1.06. That 1.06 exponent is the key. It means performance doesn't scale linearly with distance — it degrades. Double the distance takes more than double the time, because fatigue accumulates non-linearly. A 20-minute 5K runner won't run a 40-minute 10K; they'll run closer to 41:30. It's remarkably accurate for trained runners. Less so for beginners (who usually slow down more than the formula predicts) or ultramarathon distances (where nutrition, psychology, and intestinal fortitude matter more than VO2max). But for 5K through marathon? Riegel's 1.06 has held up for over 40 years.

Beyond raw fitness, I track consistency — how regularly you're training over a rolling 4-week window. The score runs from 0 to 100. High variance (training hard one week, disappearing the next) scores low. Steady, regular sessions score high. This matters because consistency is the strongest predictor of improvement. A runner who does four easy runs every week will outperform someone who does two hard sessions every other week. I don't just track your consistency — I use it to calibrate my recommendations. Inconsistent recently? I dial back the intensity. Rock-solid for a month? Time to push.

Weekly average pace is a noisy metric. One interval session can skew the whole week faster; one recovery run can drag it slower. So I use 4-week rolling averages and report trends as percentage change. The leaderboard shows these trends too. Not to shame anyone — a slower average pace might mean more easy runs, which is often exactly what a runner should be doing. Pace trends are context. They tell me where you've been. What matters is where you're going.