Couldn't make this week as away in Devon. Hopefully OK for next week.
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Couldn't make this week as away in Devon. Hopefully OK for next week.
alex_cycles
Guru
- Location
- Oxfordshire
Yeah. Considering it's a brand new unit, something ain't right. Should have been well over 170 - maybe not up to max on a 3 minute race but well above 170.
N0bodyOfTheGoat
Über Member
- Location
- Hampshire, UK
I've had two Coospo HRMs over the last 8 years, my 808(?) is ~4 years old, usually great besides when battery nearly dead.
Battery typically lasts 6-9 months, I wipe down metal contacts at end of each session and apply saliva to the two contact pads each session plus make sure it's reasonably tight around my chest. Strap gets a rinse every few months.
Battery typically lasts 6-9 months, I wipe down metal contacts at end of each session and apply saliva to the two contact pads each session plus make sure it's reasonably tight around my chest. Strap gets a rinse every few months.
ColinJ
Puzzle game procrastinator!
- Location
- Todmorden - Yorks/Lancs border
I haven't used up the original battery on mine yet. The HRM has worked perfectly every time that I have used it.
That's what I do.
steverob
Guru
- Location
- Buckinghamshire
Interestingly I had something similar happen with one of my previous Scoshe arm HRMs. Halfway through an activity my heart rate would suddenly drop to almost half of what I was expecting - instead of 140's I'd be seeing 70's. But it would still be going up and down with efforts, it wasn't like it was stuck on a number and not moving.
After a few minutes it would return to normal, but even then it wouldn't suddenly jump back up, but rather slowly increase through the 80's, 90's, 100's etc. over the course of about 30 seconds until it settled at the right number again.
The strange thing is that this only ever happened to me on outdoor rides and not on Zwift (or at least not to my recollection).
alex_cycles
Guru
- Location
- Oxfordshire
I have a few things to try. I also own a Viiiiva 4i HRM that I can try, another Coospo I bought as a spare and I could try the Coospo strap with the Garmin HRM Dual pod on it. (Edit to add: from reading up on it, I've seen a few people suggest oil or WD40 on the pod to strap connectors, which is something else that could be tried. An intermittent issue like this is likely to be an electrical connection and my assumption was that it was the strap to human connection, but it could be strap to pod.)
It could be that my skin has suddenly gone non-conductive. No idea why that could happen though - it's weird. Only some time and experimentation will get to the bottom of it, but it's annoying me now having bad data too often.
I've been using chest strap HRM ever since I decided that the one on my watch wasn't adequate back in 2018. The first strap lasted almost 5 years though. (don't make 'em like they used to
)
Last edited:
mjd1988
Guru
You’re not imagining it — what you describe is classic HRM signal dropout / mis-detection, and the pattern you’re seeing actually gives some useful clues.
I’ll break it down and then give you practical fixes.
---
What’s actually happening (and why it looks “plausible”)
> HR drops to ~warm-up levels mid-effort, still moves with effort, then slowly ramps back
That behaviour is not your heart rate — it’s the strap temporarily locking onto a harmonic or noise signal rather than your true R-R intervals.
Common failure modes:
Strap briefly reads every second beat → HR appears halved (140 → ~70)
Strap locks onto movement cadence or muscle electrical noise
Poor skin contact causes intermittent loss, and the algorithm “fills in” with bad data
The slow ramp back (80s → 90s → 100s) is the firmware re-acquiring a clean ECG signal, not your HR actually rising.
---
Why cold weather makes this worse ❄️
You’re spot on noticing the seasonal link.
Cold causes:
Dry skin → higher electrical resistance
Less sweat early in efforts
Stiffer strap material → poorer electrode contact
More clothing layers → micro-movement of the strap
Electrode gel can help — but only if the strap tension and electrode placement are already good.
---
2 electrodes vs 4 electrodes — does it matter?
Yes, but not the way marketing suggests.
2 electrodes (e.g. Coospo):
Perfectly capable when contact is good
Less redundancy when contact degrades
4 electrodes (Garmin HRM-Pro etc):
Better noise rejection
More tolerant of movement and poor contact
Still not immune to cold/dry conditions
So the Coospo isn’t “bad” — it’s just less forgiving.
---
Why it happens outdoors but not on Zwift 🚴♂️
This is a huge clue.
Outdoor rides introduce:
Road vibration
Body micro-movements
Clothing friction
Temperature swings
Sweat evaporation cooling the skin
Zwift = stable torso, constant temperature, minimal strap movement.
Arm-based HRMs (Scosche) are especially prone to this outdoors because:
Muscle activation interferes with optical sensors
Cold reduces blood perfusion to the skin
Vibration confuses the optical signal
So your Scosche behaviour fits perfectly.
---
Why Garmin training status freaks out 🤖
Garmin:
Uses HR-power relationship to estimate VO₂ max
If HR is artificially low during high power → it thinks:
> “Wow, you’re producing lots of power with low HR — then suddenly you’re not”
Result: VO₂ max crashes and training status goes weird
Unfortunately, there’s no good way to “undo” this once recorded.
---
What I’d actually recommend (in order)
1️⃣ Strap fit and placement (most important)
Strap tighter than you think, especially in winter
Position slightly higher on the chest (not slipping down)
Wet electrodes and skin (not just gel on rubber)
👉 Gel alone won’t fix poor tension.
---
2️⃣ Warm-up hack (very effective)
Before the race:
Do 5–10 min easy until you’re lightly sweating
THEN start the effort
Dry starts are HRM poison.
---
3️⃣ Try mixing hardware (your idea is good)
> Garmin pod on the Coospo strap
Absolutely worth trying.
Many straps are electrically fine but the electronics pod is the weak link
Garmin pods generally have better signal processing
---
4️⃣ Battery check (even if “new-ish”)
Cold kills marginal coin cells.
Replace with brand-name CR2032
Avoid cheap bulk cells
This fixes an absurd number of “ghost HR” issues.
---
5️⃣ If you buy another strap
Best winter-reliable chest straps (anecdotally):
Garmin HRM-Pro / Pro Plus
Polar H10 (very robust in cold)
Wahoo Tickr X (newer revisions)
If VO₂ max metrics matter to you, this is one place where spending a bit more actually pays off.
---
One final reassurance
> “There is simply no way HR should drop during a 3-min effort at 150% FTP”
Correct. Physiologically impossible unless you:
stopped pedalling
passed out
or became a reptile
So trust your instincts — this is hardware, not fitness.
If you want, tell me:
Exact strap model
How old it is
How tight you usually wear it
What base layer you use in winter
…and I can be more specific.
I as in chatgpt clearly. Isn't AI interesting/terrifying
I’ll break it down and then give you practical fixes.
---
What’s actually happening (and why it looks “plausible”)
> HR drops to ~warm-up levels mid-effort, still moves with effort, then slowly ramps back
That behaviour is not your heart rate — it’s the strap temporarily locking onto a harmonic or noise signal rather than your true R-R intervals.
Common failure modes:
Strap briefly reads every second beat → HR appears halved (140 → ~70)
Strap locks onto movement cadence or muscle electrical noise
Poor skin contact causes intermittent loss, and the algorithm “fills in” with bad data
The slow ramp back (80s → 90s → 100s) is the firmware re-acquiring a clean ECG signal, not your HR actually rising.
---
Why cold weather makes this worse ❄️
You’re spot on noticing the seasonal link.
Cold causes:
Dry skin → higher electrical resistance
Less sweat early in efforts
Stiffer strap material → poorer electrode contact
More clothing layers → micro-movement of the strap
Electrode gel can help — but only if the strap tension and electrode placement are already good.
---
2 electrodes vs 4 electrodes — does it matter?
Yes, but not the way marketing suggests.
2 electrodes (e.g. Coospo):
Perfectly capable when contact is good
Less redundancy when contact degrades
4 electrodes (Garmin HRM-Pro etc):
Better noise rejection
More tolerant of movement and poor contact
Still not immune to cold/dry conditions
So the Coospo isn’t “bad” — it’s just less forgiving.
---
Why it happens outdoors but not on Zwift 🚴♂️
This is a huge clue.
Outdoor rides introduce:
Road vibration
Body micro-movements
Clothing friction
Temperature swings
Sweat evaporation cooling the skin
Zwift = stable torso, constant temperature, minimal strap movement.
Arm-based HRMs (Scosche) are especially prone to this outdoors because:
Muscle activation interferes with optical sensors
Cold reduces blood perfusion to the skin
Vibration confuses the optical signal
So your Scosche behaviour fits perfectly.
---
Why Garmin training status freaks out 🤖
Garmin:
Uses HR-power relationship to estimate VO₂ max
If HR is artificially low during high power → it thinks:
> “Wow, you’re producing lots of power with low HR — then suddenly you’re not”
Result: VO₂ max crashes and training status goes weird
Unfortunately, there’s no good way to “undo” this once recorded.
---
What I’d actually recommend (in order)
1️⃣ Strap fit and placement (most important)
Strap tighter than you think, especially in winter
Position slightly higher on the chest (not slipping down)
Wet electrodes and skin (not just gel on rubber)
👉 Gel alone won’t fix poor tension.
---
2️⃣ Warm-up hack (very effective)
Before the race:
Do 5–10 min easy until you’re lightly sweating
THEN start the effort
Dry starts are HRM poison.
---
3️⃣ Try mixing hardware (your idea is good)
> Garmin pod on the Coospo strap
Absolutely worth trying.
Many straps are electrically fine but the electronics pod is the weak link
Garmin pods generally have better signal processing
---
4️⃣ Battery check (even if “new-ish”)
Cold kills marginal coin cells.
Replace with brand-name CR2032
Avoid cheap bulk cells
This fixes an absurd number of “ghost HR” issues.
---
5️⃣ If you buy another strap
Best winter-reliable chest straps (anecdotally):
Garmin HRM-Pro / Pro Plus
Polar H10 (very robust in cold)
Wahoo Tickr X (newer revisions)
If VO₂ max metrics matter to you, this is one place where spending a bit more actually pays off.
---
One final reassurance
> “There is simply no way HR should drop during a 3-min effort at 150% FTP”
Correct. Physiologically impossible unless you:
stopped pedalling
passed out
or became a reptile
So trust your instincts — this is hardware, not fitness.
If you want, tell me:
Exact strap model
How old it is
How tight you usually wear it
What base layer you use in winter
…and I can be more specific.
I as in chatgpt clearly. Isn't AI interesting/terrifying
ColinJ
Puzzle game procrastinator!
- Location
- Todmorden - Yorks/Lancs border
I would definitely second that. I had no response from power meter cranks donated to me by one of my cousins. I had fitted a new battery from a pack of 5 cheapos. I fitted another new battery. No response. I decided to test the cells in a little emergency front light. It turned out that 2/5 were dead despite being 'new'. 1/5 was half dead. Only 2/5 were good!
mjd1988
Guru
Yeah it can be hard to get batteries online to deliver to norn iron (thanks Brexit) so tend to be only cheap ones I get from Amazon and they are really poor
alex_cycles
Guru
- Location
- Oxfordshire
I thought your formatting was rather weird
To be honest I do pretty much all those things anyway - which is probably why I had several years without issues. What's got me curious now though is "what has changed?" It wasn't even all that cold in the garage on Friday - about 14°C.
I'm going to try various things and see what happens. I don't even mind buying new gear if it will give me another 5 years of proper data reliably. But I think perhaps the 4iiiiiiiiiiiiiii Viiiiiiiiiiiiva might be a good bet to try next. I've just put a fresh battery in it. I've had that one for a few years but not really used it much. Seems silly to just go and buy another Garmin or a Polar without trying the £60 I already bought years ago
alex_cycles
Guru
- Location
- Oxfordshire
I normally buy Maxell or Panasonic from Amazon in bulk packs of 12. They seem good. The advantage of buying 12 at a time is that if you get a good batch you are sorted for about 4-5 years
