iOS · One-time purchase · No subscription

Zone 2. Locked in.

Connect your Wahoo KICKR. Set a power target. A PID controller keeps your heart rate in Zone 2 for the entire session. Sync to Strava. Done.

Get notified at launch See how it works

Coming soon to the App Store · iOS

Justzone2 active workout screen showing heart rate, power and live chart
Wahoo KICKR ERG Mode via FTMS PID Zone Targeting Strava Auto-Upload Apple Health Apple Watch HR Live Activity Dynamic Island TCX + Power Extension One-Time Purchase Wahoo KICKR ERG Mode via FTMS PID Zone Targeting Strava Auto-Upload Apple Health Apple Watch HR Live Activity Dynamic Island TCX + Power Extension One-Time Purchase
A cyclist training indoors with Justzone2 on a Wahoo KICKR
1 Hz
PID loop samples heart rate every second and adjusts resistance continuously
±30W
Automatic power adjustment range — ramps slowly, backs off fast
$0/mo
No subscription. One purchase. Your KICKR doesn't charge monthly, neither should your app
Features

Everything you need.
Nothing you don't.

01
Zone 2 tracking & ERG control
Bluetooth FTMS
Real-time heart rate monitoring with visual zone indicators. Your Wahoo KICKR resistance adjusts via the FTMS protocol — set your target power and ride.
02
PID Zone Targeting
±30W auto-adjust
A PID controller samples HR every second using a 45-second rolling average. It nudges resistance to keep you locked in zone — gradually up, faster down. Always comfortable, never jarring.
03
Strava with full data
TCX + Power extension
Workouts upload automatically with HR, power, cadence, virtual speed, distance, and accurate calories. Strava shows the full picture — not just elapsed time.
04
Apple Watch + Live Activity
HR via Watch HealthKit mirroring or pair a BLE chest strap. Stats persist on your lock screen and Dynamic Island for the whole session. A Watch complication shows current data at a glance.
05
Apple Health + workout recovery
Workouts save to Apple Health with HR and power samples. If the app interrupts mid-session, recovery mode offers to resume exactly where you left off — elapsed time and all.
App

Five screens. All you need.

Justzone2 setup screen
Setup
Justzone2 active workout screen
Workout
Justzone2 heart rate zones editor
HR Zones
Justzone2 activity detail screen
Activity Detail
Justzone2 activity history screen
Activity History
Heart rate, your way

Bring your own sensor.

Chest strap
Polar H10, Wahoo TICKR & any Bluetooth strap
Arm band
Polar Verity Sense & optical arm sensors
Apple Watch
Wrist HR streamed straight to the app
AirPods Pro
In-ear heart rate on AirPods Pro 3
How It Works

Adaptive Zone Targeting

A PID controller monitors your heart rate every second and adjusts your KICKR's resistance — keeping you locked in Zone 2 so you can focus on anything else.

Typical 60-minute session with Zone Targeting enabled

Zone 2 0 15 min 30 min 45 min 60 min HR rising PID waits for HR to settle Cardiac drift HR slowly rises over time PID reduces power to compensate for drift
Heart Rate Power Zone 2 Band
The feedback loop
1
Measure

HR sampled every second from your Apple Watch or BLE chest strap.

2
Calculate

PID controller computes error from your Zone 2 midpoint using a 45-second rolling average.

3
Adjust

Resistance nudged gradually — ramps up slowly, backs off faster. Always comfortable.

4
Repeat

Every second, for the entire session. You keep pedalling. The app keeps you optimal.

Your fitness tracker, not just a workout tracker

As aerobic fitness improves, your body sustains more power at the same heart rate. Every session anchors to the same HR zone, making average power a direct, passive measure of progress.

  • No FTP test needed — just keep doing your sessions
  • No recovery cost — you're not exhausting yourself to measure
  • Objective progress — watts don't lie, and trends don't either

Average Zone 2 power over time

185W 175W 165W 155W Sep Oct Nov Dec Jan +23W 4 mo
Science

Why Zone 2?

It's how the pros build their aerobic engine.

  • 80/20 Polarized Training

    Elite cyclists spend 80% of training at low intensity. Zone 2 is where base fitness is built.

  • Fat Adaptation

    Train your body to burn fat as fuel. Improve metabolic flexibility and endurance capacity.

  • Mitochondrial Growth

    Zone 2 specifically targets mitochondrial biogenesis. More mitochondria = more power at threshold.

  • Sustainable & Enjoyable

    Easy effort means you can train more frequently without burnout. Build volume, not fatigue.

Resources

Learn from the experts

Zone 2 Training

Zone 2 Training Explained

The science behind low-intensity endurance training
Zone 2 Benefits

Benefits of Zone 2

Why Zone 2 is the foundation of endurance performance
Zone 2 Guide

Complete Zone 2 Guide

How to find your Zone 2 and structure your training
Zone 2 Science

The Science of Zone 2

Mitochondrial health and fat oxidation explained
Zone 2 Tips

Zone 2 Training Tips

Practical advice for getting the most from sessions
Zone 2 for Cyclists

Zone 2 for Cyclists

Incorporating Zone 2 into your cycling training plan
From the blog

Zone 2, in depth.

Guide

Getting Started: Your First Ride

Pair your trainer, set your zone, and let the app hold your heart rate in Zone 2.

 Zone 2 Life

The Easy Hour: How Zone 2 Fits a Real Life

Why riding slower around a busy schedule left me fitter, calmer and sleeping better.

 Under the Hood

The Espresso in the Algorithm

How the PID controller that holds your heart rate works — explained through coffee.
Read the blog
FAQ

Common questions.

What is Zone 2 training?

Zone 2 is a low-intensity heart-rate zone — roughly 60–80% of your maximum heart rate — where you can still hold a conversation. Training here builds aerobic base, grows mitochondria, and improves fat metabolism. It's the foundation of endurance fitness, which is why elite athletes spend most of their training time in it.

What is JustZone2?

JustZone2 is an iOS app for indoor cyclists that holds your heart rate in Zone 2 automatically. Connect a smart trainer (like a Wahoo KICKR), set a power target, and a PID controller continuously adjusts resistance to keep you in the zone for the whole session, then syncs the workout to Strava.

Which smart trainers and sensors are supported?

Any trainer that supports the FTMS Bluetooth standard, including the Wahoo KICKR range. For heart rate you can use a Bluetooth chest strap, an optical arm band, an Apple Watch, or AirPods Pro 3.

How do I calculate my Zone 2 heart rate?

A common starting estimate is 60–70% of your maximum heart rate (roughly 220 minus your age). JustZone2 lets you set all five zones directly on a visual editor, and matches Strava's zone percentages by default. See the getting started guide for details.

Does JustZone2 work with Strava?

Yes. Completed workouts upload to Strava automatically with power, heart rate, cadence, distance and calories, and the activity is titled by the zone you trained in.

Is there a subscription?

No. JustZone2 is a one-time purchase with no subscription. It's coming soon to the App Store.

Coming soon

Start building your
aerobic base.

Be first to know when Justzone2 lands on the App Store.

Get notified at launch

Coming soon to the App Store · iOS