From the training log

Running, Explained

The math and physiology behind the calculators — written by a runner, for runners.

How the Riegel Formula Predicts Your Race Times

The 1977 equation behind nearly every race predictor — and where it breaks down.

Pace vs. Speed: What Runners Actually Need to Know

Why runners think in minutes per mile, and the mental math that makes racing easier.

The Five Heart Rate Training Zones, Explained

What each zone trains, how to set them honestly, and why most easy runs are too fast.

What VO2 Max Really Means for Runners

The most quoted number in endurance sport — what it measures and what it doesn't.

More articles are added as the site grows. If there's a running question you'd like broken down by the numbers, send it in — or head back to the full calculator library.