GPS-Sport ForenRun.GPS GeneralHxM distance and speed accuracy disappointing ?
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orodiger 03.02.2010 22:40:43 UTC

My experiences with the HxM monitor

I think I bought one of the very early HxM monitors directly from Zephyr, more or less straight after RunGPS announced the support for it, as I always wanted to measure the heart rate within the application and not just read it from my Polar watch. I have to say the Polar belt and watch depsite being 10 years old worked every time and seem to provide very precise readings.

When using the HxM I mainly had problems with the heart rate being wrong or being the same for a long time. Like many of the others I tried many different things, wetting the belt, tighteing, loosening, positioning higher/lower on my chest, but nothing seemed to work. I then contacted Zephyr and they sent me a replacement. I initially seemed to have the same problem as it did not really work much better. HOWEVER, I think I then found what seemed to improve the readings and almost completely remove the dropouts or continous false readings. Here is what I did and still do

- Wet the belt well, but not drench it. A few times wet the fingers of the hand and pad each senser pad section.
- In my case I do not place the belt in the middle of my chest (as the readings were much worse), but slightly offset it to the left. I think the edge of the sensor with 'L' is almost below my left nipple.
- I also seem to notice worse readings when the belt sits on top of the rib cage, so I always make sure it sits in a gap.

For me this has produced many successful runs with satisafactory heart rate values. Hope this helps.
Dima 22.01.2010 14:14:16 UTC



Yes, speed accuracy will bring the interval training up to the next level. I think there is no universal factor, we will have to input it manually.

I'd like to add some thoughts which in some extent connected to
1. EPOC
2. Standard functional test proposal (in one of the other topics), which is considered for the next version.

EPOC is very good indicator and relevant for the whole training time.
Training time is always devided by 3 phases.
Main part parameters are usually very indicative (HREff), but very sensible to warm-up phase, so I have to use RunGPS in the following way:
1. warm-up - HR control by the eye - trainning is not started
2. training - using RunGPS as intended - trainning is started and stopped in the end
3. warm-down - HR control by the eye - trainning is not started

Is it possible to create phases inside training and count EPOC/HRE/time/distance etc. for whole training and at the same time for just main part inside, which is usually standard (2-3-4 etc km) and could be compared to each other?
By the way, if there will be any test included, it's great to compare test results during time an to some benchmarks (good, bad, see your doctor etc).
gmngueko 05.01.2010 14:32:05 UTC

in defense of HxM: some filtering needed

@Lee_Nover: in defense of HxM, I can see that the distance and speed can be usable with the appropriate calibration.
Also for the HeartRate, I see that there is some other info available that could solved the issue. I will try to experiment with those.
So my general feeling is that the rough informations are there but there is some need of filtering/calibration, that's maybe why Zephyr provide an sdk kit and doesnt' offer a full software to interact with the HxM. So I will try to implement my HR filtering based on the other data and compare it with my other HR (Garmin edge 305) to validate my findings.
Lee_Nover 05.01.2010 13:25:45 UTC



I have the same reasons and done the same things for HRM as gmngueko. Tightening/loosening the strap also doesn't make a difference. For high heart rates, there are also many drop-outs. Also, I got the HxM to monitor the speed/distance for inline sports (especially in the winter time), when the GPS is not available. For now, it seems that all of this is the HxM's fault. Is this supposed to be the "specialist for biometric sensors that has, until now, been selling professional products only" and "stands out ... and its measuring accuracy"? So far none of these were met and are, sadly, quite the contrary.
gmngueko 05.01.2010 12:52:06 UTC

I'am a geek somehow

@Admin:
first of all HAPPY NEW YEAR,
the main reason why I wanted the HxM is to have the correct value for the instantaneous speed, the GPS speed is quite bad for instant speed (in average it's ok). for the distance indeed in most cases the GPS is quite good when it works !, So for the distance calculation the HxM is mostly a backup to the GPS. indeed my internal GPS is sometimes wrong when it is cloudy and the cold start can also takes ages.
My calibration is indeed distance *= calibration factor but depending on the cadence, because I have observed that the factor is not the same while walking and while running, so I took, for the moment, the cadence to determine which factor to use (So I have two factors). I still need to try the sprinting case to see if the running factor works also in that situation.

Concerning the HR drop it is another story, I already make the belt really wet before starting the run, so this is not the issue, especially that I sweat a lot so the HR should not drop in the middle of my running ! I will try some electrode gel but I'am doubtful on that since the HxM is not made of hard plastic as other well known HRM.
And actually since I have access to the packets sent by the HxM, I can see that it's more something in the micro-controller inside the HxM as the HR reported is not always in line with the one deduced from the RR periods (or I missed something in the explanation in the sdk kit). but you can send me an email as this is maybe not the place to go into details like those.
admin 05.01.2010 11:56:14 UTC



@gmngueko:
If you experience problems with heart rate drops, you may
- make the belt real wet (never mind, it's waterproof)
- or buy some electrode gel (on Ebay or perhaps your local pharmacy)

How do your calibration factors work? Just multipliers distance *= calibFactor or something else?

Basically, why is it important for you to use the HxM and not the GPS for distance calculation? Do you want to save battery power?

gmngueko 03.01.2010 00:24:11 UTC

put some water on the belt/strap

Hi,
I had this also once and since then I put some water on my belt/strap (on the sensor part) before starting the run and now it is ok. indeed the only reliable direct measurement is the cadence which seems consistent, but speed, distance (without calibration) and especially the heartrate doesn't seem reliable when running,by my current experience and this is my second HxM!

ultimately the heartrate drops is really the most annoying issue for me, I tried with two different straps and observed the same issue.
Lee_Nover 02.01.2010 22:48:52 UTC

HxM dissapoints ..

Hi. The last time I went running I couldn't get heart rate monitoring, but cadence worked. I simply didn't get any values :/ I'll try again in a few days. I'm getting more and more disappointed by Zephyr HxM.
gmngueko 02.01.2010 16:14:43 UTC geändert am 02.01.2010 16:22:29 UTC

some calibration result

my little software is finished, I use two, configurable, calibrations factor depending on the cadence (to distinguish running and walking) , and now with that calibration the speed and distance is much more precise(1 to 2 % error) in my current experience.

the only thing which bugs me now is that the HxM hearrate reporting is sometimes dropping and drops for a long period of times, by dropping I mean that the reported value fall well below the actual value. to compare I'am wearing my other heartrate monitor (garmin edge 305). So it's not a bluetooth connection drop but something in the perceived heartrate by the HxM.
this is happening only when I'am running, while walking or even biking it seems ok.
Lee_Nover 23.12.2009 14:10:37 UTC

- cadence

if cadence is only for vertical movement, then we could use that to retract from speed and distance. if it's a sum/average of all movements, then we could use both techniques to recalculate speed and distance. for now I'll just manually fix the values in the trainings :/
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