Zx: Heart Rate Zones Training

Zx: Heart Rate Zones Training

Interval Timer & HIIT Trainer

70 ratings
17 reviews
Free
In-App Purchases

Details

  • Released
  • Updated
  • December 22, 2019
  • July 18, 2026

Features

Zx: Heart Rate Zones Training screenshot #1 for iPhone
Zx: Heart Rate Zones Training screenshot #2 for iPhone
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Zx: Heart Rate Zones Training screenshot #7 for iPhone
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About

This app acts as a personal heart rate coach for interval training. It allows you to create custom workouts or download community-made ones, guiding you to stay in specific heart rate zones. It integrates with health apps to provide detailed training insights.

Heart rate zone coaching
Custom interval workout creation
Community workout library
Guided interval training
Open mode for real-time zone tracking
Health app integration
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What's New in Zx

1.8.1

July 18, 2026

- Fixed a Studio issue preventing small intervals from being added to custom workouts.

Subscription plans

Premium Monthly

Unlock all features

$2.991 Month
How to cancel Zx subscription ⁉️
1

In-App Purchases

$14.99

Premium Lifetime Access

unlock all features forever with one purchase

User reviews

Great workout companion!

Really helpful for taking a look at hr data

Fantastic app!

I was looking for an interval timer for my own HIIT training that could also pair with my coros armband to show my heart rate.

Paying $14 for this app seemed like a no-brainer when the cheapest watch I could find to show my heart rate was $180. Now I get to see my interval timer and heart rate in the one place. It works perfectly with my coros armband and make sure I stay in the zone during night intensity intervals (while not pushing too hard above my range). Thanks for making such an intuitive and affordable app with great functionality.
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Response from developer

Thanks Nats7665! So happy you’re enjoying Zx 🤗. If you ever have any issues or feature requests, please don’t hesitate to reach out to support@oversphere.net. Best, Jillian OverSphere Support

Custom and community workouts not showing on my watch

I’m not able to use the custom and community workouts after paying for this app because they don’t show up on my watch. 😕

Response from developer

Update: Hi Sentha, we have just released a fix for the issue; apologies it took longer than expected. Please be sure to update to version 1.6. If you have any further issues, please reach out to support@oversphere.net Original response: Hi Sentha, we just responded to your support request. We are looking into the issue with workouts not syncing quickly to the Watch. They should eventually transfer over, it’s just taking longer than it originally did. Best, Jeff OverSphere Support

Good simple interface-some iwatch sync issues

Love the clear interface on the app. Can’t seem
to sync studio and community workouts to my iwatch however.

Response from developer

Hello Bents76! Thanks for using Zx! We are aware of sync issues users are having and it not being as fast as it used to be. It may take awhile but workouts should eventually sync to your Watch. We are working on that and hopefully we can get a fix out soon. If you have any other issues or feature requests, please don't hesitate to reach out to support@oversphere.net. Best, Jillian OverSphere Support

Swimming doesn't work

App is promising. While running and cycling work fine, logging a swimming workout fails. It says "Please allow Zx to 'Write Workout Data' in Health and try again.

By the way your support website is just a placeholder site. Might want to update that.

In addition to the above bug, to be useful during swimming, the alerts would have to be different patterns for above and below zone, and they'd have to be constant. For example, short quick vibrations if below zone and long slow vibrates if above zone. The same kind of constant and differentiated alerts would be useful in other situations (e.g. watch under your sleeve or glove) but especially in swimming when it's not practical to look at the watch face during a lap.
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Response from developer

Hello headquire! Thanks for trying Zx. We are now aware of the pool swimming issue and are working on a fix for it. The issue is that we aren't setting a pool lap length for the workout so it can't be started. Hopefully we can get a fix for that soon. Also! We're going to be developing an app dedicated solely to swimming and we appreciate your ideas. If you like to message us with any features or idea you'd find useful in a swimming app, we'd love to hear it! You can reach us at support@oversphere.net. Best, Jillian OverSphere Support PS thanks for letting us know about the website, it should now correctly again be redirecting to our Facebook page. :)

Developer apps

FAQ

What does Zx: Heart Rate Zones Training do?

This app serves as a personal heart rate coach for interval training. It helps you create or download workouts, guiding you to stay within specific heart rate zones during your HIIT sessions. It also integrates with health apps to provide detailed insights into your training performance.

What are the key features of this app?

Key features include guided interval training that helps you maintain target heart rate zones, the ability to create custom workouts, and access to a library of workouts created by the community. It also offers an 'Open Mode' for real-time zone tracking and integrates with the Health app for comprehensive data analysis.

How much does Zx: Heart Rate Zones Training cost?

The app operates on a subscription model with a 3-day free trial for monthly subscriptions. Subscriptions start at $2.99 per month and automatically renew unless turned off at least 24 hours before the current subscription ends. Pricing may vary based on the subscription pack chosen.

What devices is this app compatible with?

The app supports Apple Watch for its 'Open Mode' and can be used with any compatible standalone Bluetooth heart rate monitor. It also integrates with the Health app on iOS devices to provide deeper insights into your training data.

Who would benefit from using this app?

This app is ideal for fitness enthusiasts who engage in interval training or HIIT workouts and want to optimize their performance by training within specific heart rate zones. It's also beneficial for those looking to improve weight loss, fat burning, anaerobic threshold, and overall sports performance.