Heart Rate Monitor
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This section covers Bluetooth heart rate monitor pairing and configuration. Pairing, live BPM, and power-save mode are available on the free tier; advanced heart-rate analytics — zones, calibration, and recovery insights — are a Premium feature.
Overview
FitSum can connect to a Bluetooth Low Energy (BLE) heart rate monitor and display your live BPM during workouts. Live HR data improves calorie estimates, shows real-time zone data on GPS screens, and feeds into the endurance coaching engine.
Any BLE heart rate monitor is compatible — chest straps, optical arm bands, or compatible watches in HR broadcast mode.
Pairing a heart rate monitor
- Put your HR monitor into pairing mode (see its manual — usually hold a button until the LED flashes).
- In FitSum, go to Profile → Heart Rate Monitor.
- Tap Scan for devices.
- Your monitor should appear in the list within a few seconds. Tap it to pair.
Once paired, the device appears in your paired devices list with its battery level (if the monitor supports this). FitSum connects automatically when you start a workout if the device is nearby and in range.
Multiple devices
You can pair more than one HR monitor. The device marked as Primary is the one FitSum connects to first. To change the primary device, tap it in the list and select Set as primary.
Setting your max heart rate
Your maximum heart rate defines the upper boundary of your HR zones. FitSum provides an initial estimate based on your age (220 minus your age), but this is a rough starting point — individual max HR varies significantly.
To set a custom max HR:
Go to Profile → Heart Rate Monitor → Max HR and enter your measured value. The most reliable way to determine your max HR is through a supervised exercise test or by observing the highest reading you've seen during all-out effort.
If you're unsure, leave the age-based estimate until you have more data.
Resting heart rate
Your resting heart rate is used alongside your max HR in the Karvonen zone calculation method, which produces more personalised zone boundaries than using max HR alone.
To set your resting HR:
Go to Profile → Heart Rate Monitor → Resting HR and enter your value. Measure resting HR first thing in the morning, before getting out of bed, for several consecutive days, and use the average.
FitSum can also infer resting HR automatically if you grant heart rate permission to Apple Health or Health Connect and it has enough overnight HR readings.
HR zones
FitSum uses five zones. You can see your personalised zone boundaries at Profile → Heart Rate Monitor → Zone ranges.
| Zone | Description |
|---|---|
| Zone 1 | Very easy — recovery and warm-up |
| Zone 2 | Easy — aerobic base, fat-burning |
| Zone 3 | Moderate — threshold border |
| Zone 4 | Hard — lactate threshold, race-pace effort |
| Zone 5 | Maximum — all-out, sprint intervals |
Zone calculation method
By default, FitSum uses the Karvonen method (heart rate reserve), which accounts for your resting HR and gives a more accurate result than simpler max-HR–only formulas. If your resting HR isn't entered, the app falls back to a percentage-of-max-HR method.
Live HR during workouts
When your monitor is connected and a workout is in progress, a live BPM reading appears in the workout toolbar. The current zone is colour-coded.
On the GPS full-screen view, BPM is shown alongside pace and distance. The zone distribution (percentage of time in each zone) is calculated and shown at the end of the session.
Power save mode
Long workouts or GPS sessions can drain your phone battery faster. Enable Power save mode in Profile → Heart Rate Monitor to reduce the HR sampling rate. This slightly reduces the precision of zone calculations but extends battery life.
Troubleshooting
My HR monitor won't show up in the scan
- Confirm your monitor is in pairing mode (check its manual)
- Ensure Bluetooth is on and FitSum has Bluetooth permission in your phone's system settings
- Move closer to the monitor — BLE range is typically 10 metres with a clear line of sight
- Try restarting the monitor
The HR monitor shows as paired but doesn't connect during a workout
- Check the monitor's battery — low battery often causes intermittent disconnects
- Go to Profile → Heart Rate Monitor, select the device, and tap Forget. Then re-pair.
- Ensure no other app (e.g. a watch companion app) is maintaining an exclusive Bluetooth connection to the monitor
HR readings look wrong
- Ensure the sensor is positioned correctly per the manufacturer's instructions
- Chest straps: ensure the strap is snug and the contacts are damp
- Optical bands: ensure the sensor is in firm contact with skin and positioned above the wrist bone
- Warm up for 5 minutes — optical HR sensors often show inaccurate readings when cold