Forerunner 235 optical heart rate sensor is poop

I've used mine every day for months with no problems like the ones you're describing.

They pay him to say that stuff, duh.

I don't inherently trust Garmin, but I had this watch before for a few weeks, and I found the wrist HRM to be very good, apart from the known unreliability of wrist HRM at high-speed interval work.

I've had the watch since a month after it was available and have had none of the problems you describe, in fact, I continue to be impressed with just about every aspect of the watch.

optical heart rate is a lottery. it works differently for different people in different circumstances.

this blog post from Valencell (the people whose technology drives the Scosche Rhythm+) gives a little insight.

http://valencell.com/blog/2016/12/heart-rate-monitor-reviews-cant-test-just-one/

I have the 225 which I believe has the same optical HRM. I've had a lot of variability on my heart rate since i purchased it 18 mths ago. To be fair, I didn't have much luck with my previous Garmin and its heart rate strap.

The optical HRM on my Forerunner 225 is trash. On a typical run, it shows my heart rate jumping to 200+ for about the first 15 minutes or so. Then it will suddenly drop to where it should be.

The FR225 uses an optical sensor from Mio, but the FR235 uses Garmin's own in-house optical sensor. So results from one don't tell you much about the other.

Rhythmless wrote:

optical heart rate is a lottery. it works differently for different people in different circumstances.

this blog post from Valencell (the people whose technology drives the Scosche Rhythm+) gives a little insight.

http://valencell.com/blog/2016/12/heart-rate-monitor-reviews-cant-test-just-one/

I agree. My wrist doesn't seem to be a good fit for it. If I can see the green light leak I know it's collecting bad data, but even when there are no light leaks it screws up. Sometimes it cycles from good to bad to good or vice versa during a run--the first 4 miles will be bad, the next 3 will be good, the last 4 will be bad. IT tends to sync with my cadence during the "bad" cycles.

It was really helpful as I was learning how my heart rate felt compared to my effort. Now I know I can't rely on it but I'm better tuned to my body. Not sure I will buy another one if this one dies.

I got a 235 for Christmas. I've had no issues with the HRM - except when I loosen the strap too much.

I haven't done intense intervals or hill repeats yet, but have done a fartlek workout and have run some pretty hilly terrain.

I have the F35. It has the same optical sensor as 235 as far as I know.

The HR accuracy has varied depending on if it's in the "sweet spot" on my wrist. If it's off, too loose, too tight, then it will read low by 10-20bpm. Many times I'll notice it's reading low by 10-20bpm and adjust the watch, and it will start reading correctly. I am having trouble getting consistent results. It's pretty picky. I can see how it would read better on some wrists than others.

When it is in the right spot it still is a little less accurate than a chest strap, but plenty accurate for me.

Garmin's optical sensors are essentially defective products. The only reason they get away with selling them is that 99% of people don't do any intervals, don't run outside in cold weather, and also have no idea what their heart rate is supposed to be at various exertion levels, so they don't realize that it's wrong.

The TomTom Cardio Runner, on the other hand, was almost perfect. It used a Mio sensor and had a wide band that blocked any outside light. Sadly, the watch was defective in other ways, which TomTom admitted. It's a joke that one of the very first running watches with an optical heart rate sensor is STILL the only one that worked decently.

I didn't know anyone was still using HR as a way of training? Thought that fad had passed.

Another reason why you should switch to Polar. Have tried several Garmin models 405 and 225. The GPS and HR readings in both were consistently inaccurate and seemed to pick-up to much interference from outside factors.

Picked up the Polar M400 and have been very pleased with its performance.

I agree wrist fit is critical. I have very thin wrists that only just made it into their recommended range for the large strap and I think that causes the strap problems fitting snugly enough. I decided the small model was going to be too tight but only bought online so never tried it.

When its cold out mine latches onto cadence. Because of the issues with optics and processing, it's 30 seconds late to the game so if you're doing short intervals by HR, the values will be low. For just about anything else its fine. The DCR review was pretty spot on in my experience.

I have a 225 and just bought the 235. I literally this morning did my first run with the 235 and I also wore the 225 on the other arm for comparison.

I had trouble getting the 235 to lock onto my HR at the start, it was just displaying random numbers (225 was working fine) but after a few minutes of fiddling it was dropped down to match the 225.

Both HR readouts were within 2 or 3 bpm for the majority of the time. Occasionally the 225 was much higher or lower but in almost every case it was the 225 that was wrong. The only time the 235 was wrong was on the recovery after a tough hill where I got > 170bpm. It got stuck for about 100m each time on the descent before instantly dropping 15-20bpm when it caught up. Not a massive issue for me.

In terms of GPS I found the track plotted on the map was pretty nailed on apart from a few slightly chopped corners. I find the track from the 225 is often wildly out.

Overall distance was 6.01 miles for the 225 and 6.07 miles for the 235. Can't tell you which is closest, I suspect the 235 as the 225 always under measures for me (lots of cut corners).

I had GLONASS turned on and set to 1 seconds recording rather than 'smart' record.

800 dude wrote:

Garmin's optical sensors are essentially defective products. The only reason they get away with selling them is that 99% of people don't do any intervals, don't run outside in cold weather

What's the problem with cold weather? When I first saw this mentioned, I assumed people meant the sensor doesn't work through the sleeve of a coat (duh). But it sounds like there's some other issue with the cold?

HRM trainer wrote:

What's the problem with cold weather? When I first saw this mentioned, I assumed people meant the sensor doesn't work through the sleeve of a coat (duh). But it sounds like there's some other issue with the cold?

The blood vessels it is watching to determine your HR are further from the skin surface when cold. Also blood flow will be reduced in the extremities.