What is ZoneTrainer?
Two things under one name. The main one is an Android app that pairs with a Bluetooth heart rate strap and speaks up when you drift out of your target zone, turning your music down while it does. The one that touches Strava is a free web tool, the Zone 2 audit.
The audit answers a question a lot of runners never check: when you meant to run easy, did you? The site calls the trap the "Aerobic Black Hole": runs meant to be easy that drift above Zone 2 into tempo effort. You request your data archive from Strava, drop the export_*.zip on the page (or just the activities.csv inside it), set your Zone 2 range, and it builds a report: what share of your runs each year stayed in Zone 2 and what share went above it, and whether your pace at a Zone 2 heart rate has improved month to month.
It does not connect to Strava. There is no sign-in and nothing goes back to your account. The audit page says files are parsed locally in your browser, with no server uploads.
Key Features
Zone 2 audit
Enter your Zone 2 floor and ceiling in beats per minute if you know them from a watch or lab test, or estimate them with Tanaka or Fox (from your age) or Karvonen (from your max and resting heart rate). It picks up your peak heart rate from the files and works in kilometres or miles.
The report
Charts of Zone 2 pace over time and of aerobic efficiency (speed divided by heart rate) against cardiac cost, a yearly verdict on how many runs stayed easy, and a month-by-month table.
Reports you keep
Download the report as a standalone HTML file, print it or save it as a PDF, or take a JSON backup that the Android app can restore.
What it reads
A Strava export zip, activities.csv, or single TCX or GPX files with heart rate. When a full export includes activities.csv, the audit works from that file's per-activity averages and counts runs only, so it is a summary of your history rather than a second-by-second analysis. FIT files are not listed.
The Android app
Live audio alerts from any standard Bluetooth heart rate strap (Polar, Garmin, Wahoo, CooSpo and others), five zone formulas, a cadence metronome, interval programs with a custom builder, and exports to TCX and CSV. The TCX is what you upload to Strava or Garmin Connect by hand. Its Zone 2 Benchmark tracks your base pace, cardiac cost and aerobic efficiency factor over the weeks, on the phone, and exports them as a standalone HTML report (the site has a live demo). A full JSON backup and restore covers sessions, interval programs and zones.
Who It's For
- Runners doing Zone 2 blocks who want to know if the last year actually went to plan
- Anyone with years on Strava and a hunch that every easy run turned into a tempo
- Android users with a chest strap who want a voice in their ear instead of glancing at a watch
Does ZoneTrainer connect to Strava?
No. There is no Strava sign-in. You request your archive from Strava's account settings, download the zip, and drop it into the audit page. The site walks you through the steps. Workouts recorded in the Android app go to Strava as a TCX file you upload yourself.
Does it work for cycling?
The audit is built around runs: when it reads activities.csv from a Strava export, it keeps running activities and skips the rest. The Android app's alerts work on any workout with a heart rate strap.
Is it free?
The web tools are free with no account. The site calls the app "100% free, private, and ad-free" and asks for support on Ko-fi; its Google Play page also lists in-app purchases.
Is there an iPhone version?
No. The app is Android only, from Google Play or as a direct download from the site. The audit and the zone calculator run in any browser.
