Guides

Treadmill vs Outdoor Running: When Effort and Pace Diverge

Same pace, different heart rate — treadmill and outdoor running rarely match on effort even when they match on pace. Here's what actually causes the gap and how to train across both without misreading your fitness.

Treadmill Incline and Pace: Why 1% ≈ Outdoor Running

The '1% incline = outdoor running' rule is a real approximation, not folklore — here's the formula behind it, where it holds, and where treadmill pace still lies to you.

Pace vs Speed: Reading min/km, min/mi, and mph Together

Pace and speed are the same information in two different shapes — one built for planning a run, the other for glancing at a treadmill. Here's how to convert between them without losing accuracy.

Marathon Pacing Strategy: Building a Split Table That Survives Mile 20+

Most marathon blowups aren't a fitness problem — they're a pacing-plan problem that shows up 20 miles too late. Here's how to build a split table that accounts for late-race fade before race day, not during it.

Heart Rate Zones Explained: Karvonen vs. % of Max HR

Two runners with the same max heart rate can have very different Zone 2 ranges — because % of max HR ignores your resting heart rate and Karvonen doesn't. Here's the math and when the gap matters.

Why Your GPS Watch Pace Doesn't Match Your Splits

Your watch's real-time pace and your actual lap split are computed differently and will disagree, especially under tree cover or in a city — here's why, and which number to trust.

How to Estimate Max Heart Rate Without a Lab Test

The '220 minus age' formula most people know is decades out of date and systematically wrong at both ends of the age range. Here's the more accurate estimate this site uses, and when you should still get tested directly.

VDOT vs. Heart Rate Zones: Which Should You Train By?

Pace-based VDOT zones and heart-rate-based Karvonen zones measure different things. Here's when each one is more accurate, with a worked example.

Using the Riegel Formula to Predict Your Next Race Time (and When It's Wrong)

The Riegel formula is a solid starting estimate for a nearby race distance — and a poor one for predicting a marathon from a 5K. Here's the math and the limits.

Even Splits vs. Negative Splits: Which Marathon Pacing Strategy Should You Run?

Negative splitting is the textbook advice, but it isn't automatically right for every runner. Here's how to decide, with a worked pacing example.