Why I Joined F45#
I recently joined F45 to lose some weight and force myself to do more weight training. I generally prefer running or cycling outside, so this seemed like a good way to mix things up.
F45 promotes its LionHeart heart rate monitor, which connects to a receiver in the studio and provides:
- Live heart rate data displayed on screens during the class
- Calories burned and LionHeart points (whatever those are)
Since I already use a Garmin Forerunner running watch, I wasn’t interested in paying extra for a proprietary device that offers minimal added benefit. However, I soon realised there was more to the system than I initially thought.
The Strava Sync Let-down#
F45 allows you to link your account to Strava, automatically posting your workout along with the type of class it was. In theory, this should provide a more accurate calorie estimate because F45 knows what you did in class.
After linking my F45 account, I went to my first session expecting my heart rate data to sync to Strava. But when I checked the activity later - nothing. No HR data. 😢
The Reddit Discovery: ANT+ Compatibility#
A quick Google search revealed that LionHeart data is supposed to sync to Strava. Meaning, if I had a LionHeart monitor, my heart rate and calorie data would show up.
Digging deeper, I found a Reddit post that revealed an interesting detail: LionHeart just uses ANT+. That means any ANT+ heart rate monitor - like my Garmin Dual HRM chest strap or my Garmin watch - should work. 🎉
Setting Up My Garmin HRM With F45#
I chose to use my Garmin HRM over my running watch as it is typically more accurate, especially when you’re moving your arms a lot like you do at F45.
F45 requires you to enter a Device ID in the app to link your heart rate monitor, which corresponds to the ANT+ Sensor ID. To find the Sensor ID of my Garmin HRM, I checked my Garmin Edge 530 which was already paired to it, which reported a value of 863436. I entered this into the F45 app and eagerly awaited my data appearing on the class screens.
Unfortunately, it didn’t work as expected. When I went to my next class, a device showed up on the screen as Guest#11486 but wasn’t linked to my account. 🤔
The “Magic Number” Problem#
Another Reddit post mentioned a “magic number” that needed to be entered instead. This corresponds to the number after Guest#. But where did this number come from?
The issue stems from how ANT+ assigns device addresses. Originally, ANT+ used 16-bit addresses, but newer devices use 20-bit addresses. Some systems (including F45) still expect a 16-bit number, meaning we need to convert our 20-bit Sensor ID to its 16-bit equivalent.
Converting an ANT+ Sensor ID for F45#
To calculate the correct Device ID for F45:
- Convert the number from your Garmin device to Hexadecimal. Example:
863436→0xD2CCC - Drop the first 4 bits (the first hexadecimal character). Example:
0xD2CCC→0x2CCC - Convert back to Decimal.Example:
0x2CCC→11486
Once I entered 11486 into the F45 app, my Garmin HRM was recognised when I to my next class, and my heart rate data was displayed correctly on the screens. 🎯
Final Thoughts#
It’s always satisfying to figure out why something works rather than just following a vague fix. If you already own an ANT+ heart rate monitor, there’s no need to buy an F45 LionHeart — you can simply use this method to get it working.
Hopefully, this helps others looking to use their own devices with F45!