Data vs interpretation.

Pick Intervals.icuif you are a data-literate athlete who already knows what CTL, sweet-spot, polarization, and FTP drift mean, and wants a deep dashboard for free. It’s exceptional.

Pick ZoneTwoif you want the interpretation part — what to do next, what went wrong, whether you’re overdoing it — written in plain English every week, with a conversational coach you can ask follow-up questions.

Many athletes will use both. Intervals.icu as the analytics backbone, ZoneTwo as the Sunday read and the coach in your pocket.

• Depth and customization. Every chart imaginable, and you can build your own. Indispensable for power-user coaches.
• More data sources. Garmin, Wahoo, and Zwift-direct sync without a Strava hop.
• Workout builder. Design and export custom structured workouts.
• Wellness tracking. Manual daily wellness inputs (sleep, fatigue, mood) folded into the charts.
• Free, forever. David Tinker built a treasure and runs it on donations. Respect.

• Actual coaching.Someone reads your week and tells you what to do about it. That’s the whole product.
• Conversational interface.“Why was today hard?” gets answered with your specific numbers — no dashboard required.
• Plan continuity. Every new analysis knows what you executed last week and how you rated it. Adapts from there.
• Safety rails. Deterministic checks for overtraining and injury patterns, with AI forced to respond to each flag.
• Athlete-facing workout descriptions. No Zone names without concrete cues.