Yasso 800s Marathon Time Predictor

Yasso 800s Workout Guide

What Yasso 800s Are?

Yasso 800s: a famous marathon training workout popularised by Bart Yasso of Runner's World magazine in 1994. The protocol: run 800-meter intervals at a specific pace. Recovery = same time as the rep (matched recovery, slow jog). Complete 10 repetitions at race pace. The prediction: your average 800m time in minutes:seconds equals your marathon time in hours:minutes. Example: 800m in 3:30 = predicted marathon 3:30 (3 hours 30 minutes). 800m in 2:50 = marathon 2:50. 800m in 4:00 = marathon 4:00. The pattern was popularised by running coach Bart Yasso and has become a widely used, if informal, marathon predictor among experienced runners.

Why It Works (Approximately)?

The workout combines: VO2max stress (800m is near-VO2max effort for trained runners). Mental discipline (10 reps maintaining pace). Lactate buffering (working through accumulated lactate). Specificity (matched recovery prevents full clearance — mimics marathon-pace metabolism somewhat). Why it predicts (when it works): runners who can hold 10 × 800m at marathon pace seconds = (some heuristic factor) generally have the aerobic base + speed reserve for that marathon time. Limitations: not based on rigorous scientific study, more an empirical pattern noticed across many runners, so it should be treated as a rough guide rather than a precise prediction.

What do I need to know about Limitations and Variations?

When Yasso under-predicts (you run marathon faster than expected): high-mileage trained marathoners. Strong aerobic base relative to speed. Heat-acclimated. When Yasso over-predicts (you run marathon slower than expected): under-trained on long runs. New marathoners with limited 20+ mile experience. Hot/hilly courses. Yasso is best for: predictability check 4-8 weeks out. Comparing fitness across training blocks. Not for: setting target pace if VDOT or McMillan calculators disagree. Single source predictions of any kind, Yasso included, are best cross-checked against other methods like VDOT or McMillan calculators rather than relied on alone.

What should I know about Training Recommendations?

Frequency: 2-3 sessions of Yasso 800s during marathon-specific phase (weeks 6-3 from race). Not the whole training plan — supplement with: 1 long run/week (peaking 20-22 miles). 1 tempo run or threshold workout/week. 3-4 easy aerobic runs (60-75% effort). Periodisation: start with 5-6 reps, build to 10. Progressive intensity over training block. Race day execution: don't run faster than Yasso pace early. Conservative first 5-10 miles. Settle in middle. Strong finish if energy permits. Negative splitting — running the second half of the marathon faster than the first — is the pacing pattern most associated with a strong finish and a well-executed race.