The Journal
Endurance, written plainly.
Short essays on heart rate, RPE, recovery and how to train around a real life — from the coaches and engineers behind KYN.
- Comparison8 min read
KYN vs Athletica vs Runna: Choosing an AI Running Coach
An honest comparison of three AI running coaches — KYN, Athletica, and Runna — and how their training philosophies differ for amateur endurance athletes.
Read essay - Training science6 min read
Heart Rate Zones, Explained for Runners
What the five heart rate zones actually mean, how to find yours without a lab test, and how to use them to train smarter — not harder.
Read essay - Training science5 min read
RPE vs Heart Rate: Which One Should You Trust?
Heart rate lies on hot days. RPE lies when you're motivated. Here's how to use both — and when each one wins.
Read essay - Habits4 min read
How to Train Around a Genuinely Busy Week
Three rules for keeping fitness when life gets in the way — without burning out or starting from scratch the week after.
Read essay - Recovery5 min read
What a Daily Readiness Score Actually Tells You
HRV, resting HR, sleep and load all feed into one number. Here's how to read it without becoming a slave to it.
Read essay