Wrist HR - could Garmin increase accuracy for hiking?

The problem with OHR accurancy in most walking activities (like hiking) is that both cadence and heart rate are very close to each other (typically in the 90-120 range) and both may fluctuate quite quickly. That makes it really difficult to separate them, and even if you get a lock, when the two change and cross each other, it's easy to loose track of them. Also, since hiking/walking is not really hard (most of the time), it means that your bloodflow stays quite low, which makes it even harder to get good OHR readings. (Not to mention if you use hiking poles, which mask your cadence even more from the accelerometer, and cause thightening of wrist mucles, decreasing blood flow even further).

I'm afraid that this problem is really difficult to solve with current OHR technology.

With endurance running it's much easier, since heart rate and cadence are most of the time not overlapping, and tend to stay same longer (unless you do intervals, and then the watch does easily loose track), and the effort keeps your bloodflow up.

I’m intrigued why having similar cadence and heart rate makes things difficult, ive heard of “cadence lock” before, and it seems  to be an accepted thing.

But surely cadence is measured by accelerometers and heart rate by flashing lights, they should be totally independent?

I don’t get it!

Unfortunately it's not so easy. Big muscles (like thighs) working also affect the blood flow, and cause surges quite similar to the heart. The watch is actually trying to use the accelerometer to detect the cadence in order to counteract it's effect on the optical reading, but it's really tricky to do if both the heart and the legs are in almost the same rhythm. And of course the hand doesn't always move in lockstep with the legs, anyway, especially when you are hiking on a winding and uneven path.

3673816 said:

cadence is measured by accelerometers and heart rate by flashing lights,

Yep but at each step you bounce which can cause the watch to move thus changing the intensity of the reflected light - voila cadence lock. Granted likely more prominent when running but could happen when hiking due to the heavier load causing more ground impact with each footfall.

Hypothesis only!

Nice well-reasoned post. Thank you. It’s so good to see rationale thinking instead of hysterical angst.

Good points. Thanks. Still, I can't help thinking that some software changes to the HR algorithms for hiking could improve the readings.

While I agree with your observation that the cadence and the HR are close to each other much of the time while hiking, I think the watch is still too focused on detecting low HR at low speed/cadence and that it should be more receptive to changes in the HR (based on climbs, for example).

Below is a HR graph with cadence and gradient overlay for a hike I did yesterday, a fairly common type of exercise for me. It was logged with the Trail run activity. I'm at walking speed throughout the workout, except at 1:15 to 1:25 where I ran for a bit. The cadence is pretty even. The trail was quite steep from the beginning and I was wearing a 7kg backpack for extra load.

I'd estimate that my real HR from about 1 minute into the workout was above 130 and rising. I'm sure my bloodflow was just as high as on running activities. As you can see, there is a peak in the cadence where I put the marker. That's when I shook my hand vigorously to make the watch snap out of it's lock and detect my real HR. That seems to have worked. So what I did there was actually to bring my cadence up to the same level as my HR. This kind of contradicts the logical assumption that the watch uses the cadence to counteract it's effect on the OHR reading, don't you think? I lean towards the theory that the watch will not look for a higher HR because it expects it to be low because of the low speed/cadence. 

The HR readings from about 15 mins in and throughout seem pretty accurate, except the low readings at the end which might be 10-20 beats too low at times, but I'd say that's an acceptable deviation based on the conditions (low intensity, speed and cadence).

Yeah, I agree that tweaking the algorithm heuristics could have an effect (and we don't know what kind of heuristics Garmin uses for different activity types). But on the other hand, when using wrist HR, I have exactly the opposite problem when doing brisk walks and normal everyday cycling: at the beginning, the watch really easily locks onto my cadence and I have to stop for a minute to let it realize it got the HR too high. You have the problem that you have to do the same in order to get the watch to realize the HR was too low. That's an indication that it's really difficult to come up with heuristics that would work in both cases.

Also, my guess is that Garmin probably isn't factoring pace into the equation, as having more variables easily just makes things worse, not better. But that's just a guess.

BTW, have you tried the "Heart Rate: OHR vs strap difference" ConnectIQ data field? It allows you to record both wrist HR and strap HR, which makes it easier to spot in which situations wrist HR gets it wrong. For me it verified that the wrist HR is slow to react to changes in HR, which also causes it to loose the HR easily in such situations. And it's not just hiking/walking, the same happens often when running intervals.

Same for me.  Garmin warns about swimming WHR not being precise, but not about hiking WHR so I expected accuracy here. It's really disappointing. I was hoping to be able to leave my hr belt at home for hiking.

Just out of interest, here's a plot from a nordic walk I did yesterday (so it includes the poles' effect on wrist circulation). I collected both wrist and strap heart rate with the ConnectIQ data field I mentioned above. Please note that this was with Fenix 5+, so you cannot directly compare it to 945 (and of course wrist HR accuracy depends on the person somewhat anyway).

As you can see, at the beginning wrist HR clearly underestimates my HR, but at the end if often overestimates it. And it's swapping between over/underestimation a lot. So this clearly is a really difficult case for the optical HR sensor, and it's difficult for me to see how this could be improved with just a software tweak.

And to be clear, I'm personally really happy with my Fenix 5+, and I didn't expect wrist HR to be more accurate for walking (it's still miles better than my old TomTom Adventurer, which did this kind of thing for regular running as well).

grzeg1 said:

  Garmin warns about swimming WHR not being precise, but not about hiking WHR so I expected accuracy here. It's really disappointing.

To be fair, GARMIN make note of the limitations of WHR in many places, suggesting that a strap should be worn for accuracy. The information is possibly not as obvious as it could be and certainly not at the point of sale.