Training guides
From the lab.
Research-backed guides on heart rate zone training, Zone 2 cardio, and how to get the most from your Apple Watch data.
Heart Rate Zones by Age (Chart by Decade)
Your heart rate zones shift every decade as your max heart rate falls. Get a full Z1–Z5 target-zone chart by age — 20s to 70s — and find yours on Apple Watch.
Zone 2 Training: The Complete Beginner's Guide
A plain-English beginner's guide to Zone 2 training: what it is, how to find your Zone 2 heart rate, why it builds your aerobic base, and how much to do.
The Fat-Burning Heart Rate Zone: Myth, Math, and What Actually Works
The fat-burning zone burns the highest percentage of fat — not the most fat. The real science, where the myth misleads, and how to train the zone properly.
Heart Rate Zones Explained: Z1 to Z5 — The Complete Guide
What are heart rate zones, how to calculate your personal zones, and how to use Z1–Z5 to train smarter, build aerobic base, and improve VO2 max.
Zone 2 Training: The Science of Slow Cardio
Why training at 60–70% of your max heart rate builds the most durable aerobic base, burns fat, and improves VO2 max — backed by science.
Apple Watch Heart Rate Zones: The Complete Setup Guide
How Apple Watch measures heart rate, how to use heart rate zones on Apple Watch, and how Underdog turns your zone data into a competitive weekly score.
How to Improve VO2 Max: The Training Methods That Actually Work
VO2 max is the gold standard of cardiorespiratory fitness. Here's what it is, why it matters for longevity, and the most effective training methods to raise it.
Max Heart Rate: How to Calculate, Test, and Use It for Zone Training
Maximum heart rate is the foundation of all zone training. Here's how to calculate it, how to test it properly, and how to use it to set accurate Z1–Z5 zones.
Heart Rate Zones vs Pace Training: Which Metric Should You Follow?
Should you train by pace or heart rate zones? Here's when each approach wins, why HR zones are the fairer measure across conditions, and how to use both.
Best Apple Watch Workout Apps for Heart Rate Zone Training (2026)
The best Apple Watch apps for tracking workouts, heart rate zones, and fitness — free and paid picks, plus what to look for before you download.
8-Week Zone 2 Training Plan: Build Your Aerobic Base From Scratch
A structured 8-week Zone 2 training plan for beginners and intermediates. Build your aerobic base, improve fat oxidation, and raise your VO2 max — week by week.
HIIT vs Zone 2: Which Training Style Actually Works Better?
High-intensity interval training and Zone 2 cardio both promise results — but they do very different things to your body. Here's how to use both intelligently.