Vivoactive 4S heart rate completely off while steep uphill walking

Interesting workaround by trying Run. Good suggestion. 

However, this issue needs to be fixed by Garmin.

I use an 830 for cycling.  I have compared the 4S with two different HR sensors, a Garmin chest strap and a Wahoo  arm band (optical).  I found the instantaneous readings all over the map and the average always very low on the 4S.  Looking at the graphs you would think the 4S is looking at a completely different activity, person or whatever.  It is my opinion that the 4S is very inaccurate on HR.  The two external sensor seem to agree with each other  fine.

The wrist sensor technology will probably never be able to match the accuracy of the chest bands. Fortunately the 4S does also support chest bands for the days you need to have accurate heart rate logs. It is my impression that the VA4(S) is quite similar to competing watches from other brands when it comes to wrist heart rate accuracy. It can be pretty good for some activities (for me it works well for cycling and jogging), but rather useless for short intervals, sprints and strength training.

So we tested same uphill today using "Run" on Vivo4s and the HR reading was accurate this time! Thx for the tip, even I consider this as workaround and an issue Garmin should correct, seems to be software "bug".

Thank you for letting us know. It proves that this problem is not because of sensor (hardware) limitation software issue but because of software limitation imposed on Walk app. Garmin should fix it.

The different activity types will provide quite different heart beat readings by design. The sensors give out rather noisy signals that must be filtered with algorithms using probability and guessing based on what it thinks you are doing. It can sometimes give very strange results if you are not doing the activity the typical way. 

I do not see how walking uphill is unusual activity. A device marketed as sports watch should definitely be able to record it properly.

Moreover, sensors on the watch can do it obviously when Run is selected, but it is a software issue in Walk app. 

The typical runner has a quite high heart rate, while the typical walker has a rather low heart rate. I assume Garmin is using this knowledge to tune the algorithms, making the walking app most accurate at low/moderate heart rates, and running most accurate at higher heart rates. 

You can also try to do two similar workouts with the cardio app and the yoga app. You will see the same difference.

As users, we would of course want apps that work perfectly over the entire range of possible heart rates, but the technology is not quite there yet. I am sure they are working on it, using all available data to make better choices. That can lead to situations where a non typical user can get worse results than with more generic algorithms.

I understand what you are saying.

However, I am not looking at that as an excuse for the situation that sports watch fails miserably when measuring heart rate during walking, which clearly indicates that algorithm used is not good enough. Either it is fixed to work properly or it should be disclosed what are limitations and in which scenarios, so that users know before spending so much money on a watch.