What’s the Optimal Distance for Your Marathon Long Run? - Lee Grantham

Aug 13, 2025

Intro

This is a quick summary of What’s the Optimal Distance for Your Marathon Long Run? from Lee Grantham. It’s a great watch — we’re breaking it down so you can try the workout today. Be sure to check out the full video for all the details.

Key Points

The goal of your long run is to boost endurance, aerobic capacity, stamina, and mental toughness while getting comfortable at marathon‑pace effort.
Instead of always increasing distance past 35 km, bring the long run back to 25‑30 km and add race‑pace or faster segments to train specificity.
Work on your strengths but also target your weak areas. If you’re great at shorter distances, that speed is an asset you can sharpen with specific sessions, like those in our guide to Mastering 5K Speed: Proven Interval Strategies to Cut Minutes off Your Time. The key is to also address your weaknesses, like running at marathon pace, to turn them into strengths.
Use a mix of steady‑state, threshold, and progressive runs to stay fresh, improve confidence, and set up a negative‑split race.

Workout Example

Typical 25 km “medium” long run (≈15‑16 mi)

First 5 km – easy pace about 20 % slower than your target marathon pace (e.g., 4 min/km if marathon goal is 5 min/km).
Middle 15 km – run at marathon pace (e.g., 5 min/km).
Final 5 km – pick up to a faster pace (around 4 min/km, roughly 20 % faster than marathon pace). This segment simulates running on tired legs and will feel closer to your 10K effort. For more on that kind of intensity and pacing, check out our guide on Mastering the 10K: Proven Training Plans, Pace Strategies, and How a Smart App Can Elevate Your Performance.

Progressive 24 km run (split into three 8 km blocks)