Team RunRun coach Ryan Sheehy gives three concrete examples of how varying your race distances can make you better at all of them.
For four years, I built and rebuilt for ultras — my first 50K, then a 100K, then 50-milers, then two cracks at 100 miles. When I finally crossed the line of my first 100-mile finish, I knew I had two choices: go longer, or go shorter. Another 100-mile block felt daunting — not that I didn’t want it, but the thought was overwhelming. So I went the other way. Recover, build speed, race a 5K. I’d give myself some time, I thought. Five weeks after the 100-miler (whoops!), I lined up and PR’d by a minute and twenty seconds.
That wasn’t a fluke. It was physiology doing exactly what physiology does.
Here’s the thing most runners miss: race distances aren’t separate sports. They’re different ports to the same ocean. Train for one, and you unlock adaptations that quietly make you better at the others. Below are three ways to use a “wrong” distance to sharpen the one you actually care about.
The Mile Sharpens Your 50 miler
Think of your aerobic system as a big diesel engine and your top-end speed as the redline. Most ultrarunners spend years building the engine and never touch the redline. The problem? When you don’t raise your ceiling, you’re leaving performance on the table.
Training for a fast mile improves your running economy and VO2 max — meaning your goal marathon pace starts to feel like a jog. The effort that used to sit at an 8 out of 10 drops to a 6. You’re not running harder; the same speed just costs less. Drop a short speed block into your base phase, even just one workout a week, and watch your easy paces float down on their own.
The Ultra Builds the Base for Your 5K
This one feels backwards, so stay with me. How does running absurdly far make you faster over three miles? Because volume is the foundation everything else stands on.
Ultra-style training — long, slow, time-on-feet work — expands your aerobic base dramatically. You build more mitochondria, more capillaries, a bigger fuel tank. Think of it like widening the highway: once you’ve got ten lanes instead of four, you can move a lot more traffic before things jam up. Spend a block stacking aerobic volume, then transition to sharp 5K/10K work, and you’ll have a deeper well to draw from when the pace gets ugly. The speed sits on top of the base, not instead of it.
The 10K Teaches Your Body to Buffer (and Suffer)
The 10K and half marathon live right around your lactate threshold — the redline where your body produces lactate faster than it can clear it. Racing these distances trains you to push that threshold higher and hold discomfort longer.
That’s a transferable skill. A higher threshold means you can hold a harder pace in your 5K before the wheels come off, and it means your marathon “comfortable” zone gets faster too. It also builds something you can’t measure in a lab: the mental callus of staying composed while everything in you wants to back off. Race a few 10Ks during a marathon build and you’ll arrive at the start line tougher in both body and head.
The Takeaway
Your race calendar shouldn’t be a straight line of the same distance over and over. The best runners treat distances like cross-training for each other — borrowing speed from the short stuff, endurance from the long stuff, and grit from the in-between. Variety isn’t a distraction from your goal. It may be the best route to it.
Ryan is a coach with Team RunRun. To learn more about him or to work with him, check out his coach profile.