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Cadence Lock Issues

Hi,

I figured I would make a separate post for this - mainly because the forum search function makes it really hard to find information relating to the Cadence lock issues in other posts.

So I've now done 3 runs with my Forerunner 235 - once with firmware 3.10, once with firmware 3.13b and once with firmware 3.13b but with a Wahoo TICKR Run chest strap HRM attached.
Run 1 https://connect.garmin.com/modern/activity/975234830 (3.10 firmware and 235 optical HRM)
Run 2 https://connect.garmin.com/modern/activity/977945044 (3.13b firmware and 235 optical HRM)
Run 3 https://connect.garmin.com/modern/activity/978756577 (3.13b firmware and Wahoo TICKR Run chest HRM)
If you expand out the Heart Rate graph and then add an overlay for Cadence you'll better see the cadence lock issue.
For all intents and purposes it has been the same run - though you'll see that I had to stop on the last two runs and re-route due to exhaustion - I'm not a runner and I'm pushing the limits of my current ability trying to improve my cadence and pace, which may or may not be working lol

The second run (the first with 3.13b) clearly demonstrates the cadence lock problem - my BPM and SPM are the same almost the whole way through.
The run I did today with the HR strap shows a clear difference between BPM and SPM.
The HR is a lot less spiky too - but that is to be expected with a chest strap vs. a wrist based HRM, and is still less spiky than the first run with 3.10 shows.

Anyway - does anyone know if there is a way to fix this? Has anyone tried the latest firmware release (3.20) to see if that helps? Or does anyone know if Garmin are aware of the issue and if they're working on it?

0 philippe.berini over 9 years ago

Cadence lock = crossover problem -> known issue for optical sensors based on that link posted in another thread : http://www.edn.com/electronics-blogs/embedded-insights/4440217/Optical-heart-rate-measurement-s-top-5-challenges - apparently a company called PerformTek has it under control.

I was doing a little research on this topic, since I would like to understand better what exactly this crossover problem is (just out of curiosity).

If I understand correctly from what I've read, the sensor picks up heart rate by changes in bloodflow, which in turn changes how the light is reflected in the skin back to the sensor. Movement also leads to changes in bloodflow, so blodflow under the sensor changes accordingly to step rate. This is one kind of "noise" that gives trouble to reading the HR.

Here's what I found, if someone might be of a curious nature like me :)

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PerformTek is the name of the sensor technology, Valencell is the company.

Here's a short interview with the co-founder: http://www.mdtmag.com/blog/2015/10/sophisticated-biometric-monitoring-solution-ready-very-active-users

He says:

As with the traditional PPG approach, PerformTek sensor technology measures weak blood flow signals by shining light at the skin with an optical emitter and sensing the scattered light with a photodetector. The key difference is that the PerformTek signal extraction method takes it a step further, employing motion-tolerant PPG, which actively removes noise signals associated with motion artifacts (such as skin motion and footsteps) and environmental exposure (such as sunlight) from the photodetector signal using a method invented and patented by Valencell's R&D team. The result is a cleaned-up signal that contains more accurate information about blood flow. Because blood flow modulates with heart rate and respiration rate, PerformTek-powered algorithms can accurately extract heart rate, RR-interval, respiration rate, and other blood flow parameters from the photodetector signal even during intense exercise.

Some more from that company: http://www.valencell.com/blog/2015/10/optical-heart-rate-monitoring-what-you-need-know

Their sensor seems to be used in the Scosche Rythm+. Would be interesting to see if there's also reports for that on cadence lock issue.

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Some more from a patent document: http://www.google.com/patents/US20150018636

...

PPG sensors measure the relative blood flow using an infrared or other light source that projects light that is ultimately transmitted through or reflected off tissue, and is subsequently detected by a photodetector and quantified. For example, higher blood flow rates result in less light being absorbed, which ultimately increases the intensity of the light that reaches the photodetector. By processing the signal output by the photodetector, a monitor using PPG sensors may measure the blood volume pulse (the phasic change in blood volume with each heartbeat), the heart rate, heart rate variability, and other physiological information.

...

However, PPG sensors are also highly sensitive to noise, and thus are more prone to accuracy problems. For example, a motion component of a user, e.g., a step rate of a jogger, is often as strong as or stronger than a heart rate component, which may corrupt a heart rate measurement. U.S. Pat. No. 7,144,375, which discloses using an accelerometer as a motion reference for identifying the potential step rate component(s) of a PPG sensor output, provides one possible solution to this problem.

...

The solution disclosed herein removes a step rate component from a measured heart rate by using one or more filtering techniques when the step rate is close to the heart rate. In general, a difference between the step rate and the heart rate is determined, and the step rate is filtered from the heart rate based on a function of the difference.

...

0 philippe.berini over 9 years ago

I considered buying FR230 + Scosche Rhythm+ instead of the 235, but then I found this thread: https://forums.garmin.com/showthread.php?94468-620-with-Scosche-RHYTHM-any-experiences

Unless new info is available, it seems that the heart rate variability data transmitted by the Rhythm+ is either inaccurate or nonexistent. I understand that the HRV data is needed to build the Firstbeat physiological model(s). Without the insight provided by Firstbeat (training effect, recovery time, VO2max) the HR data are much less valuable for me.

If someone had a ANT+ receiver for an iPhone as well as a Bluetooth chest strap HRV readings could be compared. I have only the latter. Elite HRV is a good app for that.

0 Former Member over 9 years ago

I did some cardio/interval work this evening on my Bowflex Max Trainer. The 235 appears to have locked cadence with my Max Trainer because it was consistently reporting back a heart rate of 40 to 60 bpm which coincides with the intervals. My actual rate was probably in the 110's to 150's... I'm going to put my fitbit back on and compare the data to see the difference. I'm running the new firmware so they haven't fixed this problem yet. I did go for a run yesterday on the new firmware and it seemed to work okay. So resting heart rate and steady pace running work okay with the 235 and it's broken when trying anything else.

0 webvan over 9 years ago

I considered buying FR230 + Scosche Rhythm+ instead of the 235, but then I found this thread: https://forums.garmin.com/showthread.php?94468-620-with-Scosche-RHYTHM-any-experiences

Unless new info is available, it seems that the heart rate variability data transmitted by the Rhythm+ is either inaccurate or nonexistent. I understand that the HRV data is needed to build the Firstbeat physiological model(s). Without the insight provided by Firstbeat (training effect, recovery time, VO2max) the HR data are much less valuable for me.

Unfortunately according to some testing done here http://www.gpspassion.com/forumsen/topic.asp?TOPIC_ID=149812 it doesn't seem like the FR235 is using real HRV data to produce the numbers we are seeing on the watch :-(

0 gpb11 over 9 years ago

Unsurprising given that optical HRM measures secondary (or arguably tertiary) effects of the heartbeat instead of a chest straps direct measurement of the heart's electrical activity. There's simply a lot of noise / inaccuracy imparted by measuring changes in light reflectivity of tissue based on blood pressure waves in your wrist that had to travel through your moving / flexing arm vs simply reading the electrical fields across the heart itself. Yes a lot can be done with signal analysis and noise elimination, but IMHO at this time if you need real, accurate HRV data you *need* to be using a chest strap.

0 philippe.berini over 9 years ago

Unfortunately according to some testing done here http://www.gpspassion.com/forumsen/topic.asp?TOPIC_ID=149812 it doesn't seem like the FR235 is using real HRV data to produce the numbers we are seeing on the watch :-(

Thanks for sharing that post. Interesting, but I'm not sure if the argumentation is correct. He shows that heart rate being more volatile on the chest strap than on the optical sensor. That is just the HR number read every second.

However, the RR intervall is the time in miliseconds BETWEEN two heartbeats. Depending on how much this varies you get the variability of that.

The Polar graph seems to show a data point every second (I believe). The FR235 graph has different time-space between two data points. I counted 27 points there which could mean it was maybe broadcasted in "smart recording". Not sure though if and how that works and what data actually CAN be broadcasted.

I'm not a scientist, but I think I've read a lot about this in the last few weeks and still having a tiny amount of ideas about math prevailing in my head from my university times :rolleyes:

Am I seeing this wrong?

I also think that RR data is NOT being recorded in a data file from a sportswatch, at least I couldn't find any hints about RR intervals neither in a FR235 TCX nor in a TCX exported from Polar (H7/Polar Beat). But the H7 can read and broadcast thise intervals, as I'm reading this with the EliteHRV app.

Therefore I would love if someone could actually read the RR data over broadcast mode (if this is even possible at all). See here: https://forums.garmin.com/showthread.php?337319-HRV-Check-anyone-has-an-ANT-Receiver-for-their-Smartphone

0 webvan over 9 years ago

Right, but then what's the worth of the VO2Max or Recovery data we're seeing on the FR235 ? And wouldn't it be better just to get an FR230 with a Scosche that will also stream data to a Bluetooth device if need be ? I guess the FR235 has 24x7 HR tracking but that feature's just been significantly "downgraded" to preserve battery life. Not sure what to think at this point!

0 gpb11 over 9 years ago

I'm unsure how a 230 + Scosche would be "better", but you've not really defined the term. If you're talking about gaining greater accuracy of HRV data, then you need to get away from optical HRM and put on a chest strap. Personally, in comparing a 230+Scosche to a 235 you end up with two devices to keep up with and ensure are charged, plus you get a second tan line. I'd rather have the one device to mess with and I have zero use for bluetooth transmitted data, so for me the 235 is the "better" choice. :cool:

I wouldn't consider anything derived from OHRM based HRV data as anything more than a "curiosity". If you want decent HRV data you need a chest strap. If one is interested in truly accurate VO2 max, go get a sports fitness test done. Even chest strap HRV derived VO2max figures are estimates.

You say the 24x7 monitoring has been significantly downgraded. Respectfully, that claim seems a bit hyperbolic given the short timeframe in which the firmware has been out and the rather limited data presented to establish that case. Nor is there anything to suggest the latest update is the final one and no further adjustments will occur. (and again there's the whole definition of terms thing, be careful not to assume everyones use cases are the same)

My recommendation (you said you're unsure what to think) is chill out and go for a run. We're dealing with a new Garmin device and as anyone who's been using Garmin sports watches for a few years knows, the first few months can be turbulent times. :cool:

0 the5krunner over 9 years ago

I just re-checked if HRV data are required for all Firstbeat-generated insights.

1. VO2max. According to Fig. 2 in the following whitepaper (http://www.firstbeat.com/app/uploads/2015/10/white_paper_VO2max_11-11-20142.pdf) only HR (as well as speed from accelerometer or GPS) is required. There is no mention on HRV in this paper.

2. Training Effect. According to the paper on TE (http://www.firstbeat.com/app/uploads/2015/10/white_paper_training_effect.pdf) the inputs are excess post-exercise oxygen consumption (EPOC) and the activity class, which is the user's input in Garmin Connect. Now, according to Fig. 2 in the EPOC whitepaper (http://www.firstbeat.com/app/uploads/2015/10/white_paper_epoc.pdf) the HRV data ("R-R intervals") are indeed required, but only to extract the respiratory rate and HR. My guess is that - when FR235 is in the optical HR mode - the respiratory rate is estimated, and only the HR data from the optical sensor are employed.

This is a quote from Firstbeat (not support) to me:"EPOC/TE can be estimated also without HRV, but HRV brings more accuracy to the analysis. With HRV we can for example utilize respiration rate information when analyzing the EPOC/TE. "

basically the expansion and contraction of the lungs shows up in changes to heart beat. so breaths per minute can be measured. I imagine oxygen consumption is further inferred from that and other things.

optical and HRV: my understanding is that TomTom are the closest to this with already-released hardware. apparently the runner 2/spark needs a firmware update and voila HRV will be there. maybe. perhaps.

I've tried various optical HRMs and quite a few of them DO give HRV data and SOMETIMES it seems to match strap-based HRV data. I think it's probably coincidence though.

0 the5krunner over 9 years ago

I'm unsure how a 230 + Scosche would be "better", but you've not really defined the term. If you're talking about gaining greater accuracy of HRV data, then you need to get away from optical HRM and put on a chest strap. Personally, in comparing a 230+Scosche to a 235 you end up with two devices to keep up with and ensure are charged, plus you get a second tan line. I'd rather have the one device to mess with and I have zero use for bluetooth transmitted data, so for me the 235 is the "better" choice. :cool:

I wouldn't consider anything derived from OHRM based HRV data as anything more than a "curiosity". If you want decent HRV data you need a chest strap. If one is interested in truly accurate VO2 max, go get a sports fitness test done. Even chest strap HRV derived VO2max figures are estimates.

Agree.