Odd heart rate behaviour on 235

Odd behavior par for the course

Based on 20-30% of the threads on this forum being about how the built-in HRM is odd in some way or another, I have to conclude it is far less than reliable. My own experience with it has me strapping on a chest monitor when I want to track HR accurately. YMMV.

Something you need to be aware of is that running the Heart Rate Monitor 100% of the time would shorten the charge life of the battery rather quickly because those LED's consume a good bit of energy. If you want an example of this take a look at the thread where the heart rate monitor won't shut off. Per the reports in that thread when the heart rate monitor gets "stuck" on it drains the battery in about 4 hours.

So, what Garmin does with the wrist monitor is use a sampling scheme with a computer algorithm "filling in the blanks". As a new user your watch is using "canned data" to guess at how your heart rate changes in response to activity. Two things will help a bit with this issue. One is to make sure you have entered accurate User Data, meaning age, weight, etc. The second is to get out and start recording a variety of activities, such as Running, Walking, Bicycling, etc. By entering accurate User Data you get the watch working to data tables that apply to someone of average condition for your sex, height, weight, and age. By then building up a record of your individual response to activity that predictive algorithm will become more accurate at predicting your individual response to activity. However I'll warn you right not that you will not EVER see minute to minute accuracy.

I will also warn you that the Forerunner 235 is somewhat heavy and as a result can go into what is called Cadence Lock during an activity such as running due to movement of the watch on your wrist misinterpreting that movement as a heart rate trace. Finally, the 235 uses a single axis step counter and that can cause the heart rate monitor to go really haywire if you are doing something like playing a drum set or using a hammer, that will send the step counter into overdrive and the heart rate reading into orbit.

There are two options to address the Cadence Lock issue with the 235.

One is to snug up the watch good and tight, which I have tried doing. It mostly works but you also need to wait for a good solid heart rate lock before you start your activity or it can take forever (15 minutes or more) for the 235 to get a heart rate lock when you are moving. Note, when you select an activity such as Run you'll see a Status Bar at the top of the screen. You'll know you have a good heart rate lock when the heart symbol becomes steady, if it's flashing the watch doesn't have a lock. Usually it can get a lock in a half minute or so but there have been times when it's taken as much as 3 minutes for me. I'll also note that I have too many occasions where the wrist heart rate went off track during a "Run" that I don't consider it accurate for anything more intense than a slow walk.

The second option for a good solid heart rate recording is to use a chest monitor. If you maintain the chest straps properly ( currently have 6 straps) IMO there is nothing more accurate than the chest monitor. Another plus is they link up with the watch nearly instantly so no waiting around for the wrist heart rate.

Yeah, I didn't pull any punches. The Forerunner 235 is NOT perfect or even close.

IMO the step counter is really poor when compared to the 3 axis step counter used in the base model Forerunner 15. The major issue with the step counter is that if your wrist isn't moving due to doing something as simple as putting your hand in your pocket your steps won't be counted. With the older 15 the vertical motion sensor would record steps if you had your hands in your pockets, were pushing a snow shovel or grocery cart, or any other activity where the arm motion is restrained. In addition the step counter on the 235 is very easy to "spoof" just by swinging your forearm while the older model 15 was impossible to spoof.

Then there is the Predictive Algorithm for the wrist monitor which can be viewed as a Necessary Evil at times. This algorithm is highly dependent on the VO2 Max you have established by Running outside on Pavement using the GPS. Note how specific that statement is. Running on grass will totally trash your VO2 Max due to the extra "drag" involved. Not using the GPS or a GPS record made defective due to tree cover, etc. will trash your VO2 Max. Using ANY kind of Indoor Fitness Machine will trash your VO2 Max estimate. As a result for many users who cannot Run on Pavement the VO2 max estimate, calorie estimate, Recovery Advisor, and all the other VO2 Max based estimates are pretty much wrong. Which means the Predicted Heart rates will also be way off at times. This is especially prevalent if the Recovery Advisor is claiming you need to rest for 40 hours or more.

So, some good news is the 235 is a good sleep tracker and useful for those concerned about Sleep Apnea. It's also fairly good at tracking your heart rate if you are working at a computer or watching the boob tube. It's also a very good Runners Watch for those who live in climates that permit running year round. I will also say that with the GLONASS option enabled getting a solid GPS lock is normally so fast I can't get my house door locked before I have a GPS lock, the GPS with GLONASS performance has been 100% flawless for me.

As for those who are outside this rather narrow definition, the first fitness watch maker who produces a design focused on older athletes or those limited to using fitness machines for most of the year will stampede to that product. Garmin, are you listening? Get your act together, the step counter in the 235 is junk and you really need to address the Baby Boomers. We are a large segment of the population and you'll find out how large if one of your competitors starts to focus on serving us Boomers.