How Cadence Lock/Bad HR Data Ruins Your Garmin’s Metrics
Garmin watches are packed with advanced health and fitness tracking features, but their accuracy depends heavily on one key factor: heart rate (HR) readings. If your HR data is wrong, it can wreak havoc on everything from VO2 Max estimates to suggested workouts and recovery time.
One major culprit of bad HR data? Cadence lock.
What Is Cadence Lock?
Cadence lock happens when your Garmin mistakenly detects your running or cycling cadence (the number of steps or pedal strokes per minute) as your heart rate.
For example, if you’re running at 180 steps per minute (spm), but your heart rate is actually 135 bpm, your Garmin might register, say, 183 bpm instead. This can happen when:
- The watch is worn in a bad position and not tightly enough on your wrist.
- The optical HR sensor is dirty or misaligned.
- You’re gripping something tightly (e.g., cycling handlebars or dumbbells), which affects blood flow in the wrist.
And even if you’re not running or cycling, bad HR readings can still occur. If your Garmin isn’t positioned correctly, it can randomly register ridiculously high HR numbers—even when you’re at rest!
Now, let’s see how this bad HR data can ruin your Garmin’s health metrics.
All the Garmin Health Metrics that Bad Heart Rate Data Messes Up
1. VO2 Max
VO2 Max is a key metric Garmin estimates based on your workouts. It’s an important indicator of:
- Longevity: Studies show higher VO2 Max is linked to a longer lifespan.
- Performance potential: The higher your VO2 Max, the better your endurance..
How is VO2 Max actually measured?
In a lab, it’s done with a mask that measures your oxygen consumption while you run or cycle at increasing intensities.
How does Garmin estimate it?
Since Garmin can’t measure oxygen intake directly, it uses:
- Heart rate data from runs or power-based bike rides.
- Pace/speed data to estimate fitness level.
So, if your HR readings are too high due to cadence lock, Garmin will think you’re working way harder than you actually are to go a given speed—leading to deflated VO2 Max estimate.
2. HR Zones
Your HR zones are crucial for:
- Training intensity (e.g., Zone 2 for endurance, Zone 5 for max effort).
- Estimating calorie burn.
- Tracking fitness progress.
Garmin auto-detects your Max HR and Lactate Threshold HR (LTHR) if you’ve done hard enough workouts.
But bad HR data can:
- Overestimate Max HR, leading to wrong HR zones.
- Inflate Lactate Threshold HR, making workouts seem easier than they are.
Since HR zones are based on:
- Max HR (traditional method)
- Max & resting HR (Heart Rate Reserve method)
- LTHR (Lactate Threshold method)
any errors in HR readings will throw off all your HR zones.
3. Acute Training Load
Garmin assigns an Acute Training Load to each workout based on HR intensity. If your HR is too high due to cadence lock, the watch thinks you worked way harder than you did—and assigns an absurd Training Load.
Example 1: A 10-Minute Calisthenics Workout Gone Wrong
One day, I did a 10-minute workout consisting of doing 25 pull-ups outside in a calisthenics park, walking a couple minutes to go back inside, and then doing 50 bicycle crunches and 50 push-ups.
But during my short walk, my Garmin locked onto my cadence for 53 seconds, thinking I was in Zone 5 (maximum effort)!
The result was an Acute Training Load of 59.
To give you an idea of how high high that is, these were the acute training loads of other workouts I have done recently:
- 8 km dog walk (avg HR: 68 bpm): 4
- 25 km recovery bike ride outdoors (easy pace, but with hills): 40
- 6 km Zone 2 run: 100
- 20 km Zone 2-3 training run: 232
A 10-minute calisthenics workout (which was actually more like 4 minutes, since I was resting or walking easily for 6) shouldn’t have had so much more of a training impact than a 25-km bike ride. In fact, I do the pull-ups, crunches, and push-ups daily, so I know how much the Acute Training Load should actually be. Most of the time it registers as a 4.
Example 2: A Super Easy Bike Ride Becomes “Brutal”
I did a 30-minute indoor bike ride while studying French on Duolingo. My HR was under 80 bpm, and I wasn’t breathing hard at all. For this, the expected training load should have been more like 6. I know this is nearly the same as just sitting in a chair, but that’s essentially what you’re doing when you’re perched on a bike, slowly spinning the pedals at the lowest resistance—just like I was.
But my Garmin recorded:
- 13+ minutes of Zone 5 (>159 bpm).
- Max HR of 199 bpm (which is impossible for me).
- Acute Training Load: 343! That is way more than my 20 km run the day before.
This is how bad HR data can completely ruin Garmin’s Exercise Load metrics.
4. Training Load
Your Training Load is a rolling 7-day average of your the Acute Exercise Loads of your workouts. If one workout has a false high Exercise Load, your entire Training Load goes up. If it stays too high, Garmin will tell you to rest too much or think you’re overtraining.
The worst part?
Garmin doesn’t recalculate Training Load even if you delete the bad activity in Garmin Connect and on the watch. The incorrect data is permanently baked into the watch’s calculations.
5. Daily Suggested Workouts
Not all Garmins have this great feature. But those that do rely on:
- Training Load
- Recovery time
- Upcoming race goals
If your Training Load is artificially high due to bad HR readings, Garmin will keep suggesting recovery or rest days, preventing productive training.
6. Recovery Time
As recounted in my post entitled, “You’re Wearing Your Garmin Wrong: How to Improve Heart Rate Accuracy,” my friend Angie noticed something strange. Her Garmin Forerunner 265S told her she needed 96 hours of rest after a workout—even though none of her workouts exceeded an hour and she didn’t feel particularly tired.
When we checked her Training Load, it was insanely high. Why?
Garmin thought her F45 workouts were in Zone 4-5 due to incorrect heart rate readings, when in reality, she was in Zones 1-2.
In other words, the watch believed she was constantly doing extreme workouts—so it kept recommending unnecessary recovery.
Once she started wearing her watch on the inside of her wrist during exercise, her heart rate measurements became a lot more accurate. A week or two later, her Training Load had normalized.
7. Fitness Age
Older Garmin models based Fitness Age only on VO2 Max, and can (amusingly) say your fitness age is 20 when you are 49. However, newer models won’t let your Fitness Age be more than 10 years younger than your actual age.
Newer Garmins estimate Fitness Age based on:
- VO2 Max
- Activity levels
- Resting HR
- BMI
Regardless of whether you have an older or newer Garmin, since VO2 Max is affected by bad HR data, your Fitness Age will also be inaccurate. There is a good chance that it will say you are even older than you feel, which is not encouraging.
8. Stress & Body Battery
Garmin uses HR data to estimate stress levels.
- If HR is falsely high → Garmin thinks you’re stressed.
- If stress is high → Body Battery drains faster.
So if your HR is wrong, your Garmin might think you’re more stressed and fatigued than you really are.
Conclusion: GIGO—Garbage In, Garbage Out
Garmin watches provide great insights—but only if HR data is accurate.
Therefore, be sure to wear your watch snugly and positioned correctly (see my guide: You’re Wearing Your Garmin Wrong) when you are exercising. If you notice cadence lock, stop and fix it.
If HR tracking is too much of a hassle, I suppose you could turn it off entirely—I actually have a friend who does this. But then you’ll lose most Garmin insights and leave you with just a GPS watch that tracks time and distance. In other words, you wouldn’t be using your high-tech Garmin to its full potential or benefiting from its valuable insights.
Remember: Bad data = bad training guidance. So keep your HR readings accurate!
