HRM Blues

When I first started thinking about doing triathlon, indeed before I even ran 10K all in one run, Sarah had bought me a Garmin 910XT triathlon watch. This watch came with the familiar chest strap heart rate monitor, although this one was the “premium” version which meant that the strap was a bit nicer.


I never bothered seriously reviewing this device because it generally worked OK, until it didn’t. To be clear I never really liked the chest strap because even though it was the ‘premium’ version, it still wasn’t very comfortable. After about three months my heart rate monitor would randomly stop reading heart rate (drop out) or read so ridiculously low (reading 85 when it should be 160) that the data couldn’t be trusted. Compounding the issue, when it would simply drop out, garmin calculated the heart rate as zero when it wasn’t reading which skewed the average. A 10KM tempo run would show up with an average heart rate of 107, which is hardly accurate.

After reading a review by DCRainmaker (the go-to source for sports products testing) I decided to try the Scosche Rhythm + heart rate monitor which sports an optical heart rate monitor.


This monitor fits on your arm, either on your forearm or bicep, and reads your heart rate by peering into your capillaries using three pulsing lights. Medical offices have used this technology for years by putting your fingertip into a little clamp. Those can read both HR and oxygen use, which is cool.

A quick note on reading heart rate – as unlikely as it seems that you could calculate HR by staring (through the skin) at your capillaries, keep in mind the way the old style monitors work. Contrary to the way a lot of people think they work, the chest straps do not “listen” to your heart beating like a stethoscope. The chest strap type monitor detects the electrical current from your heart and using that data it calculates your heart rate. It is no surprise that sweat and water and slight misplacement can cause the chest strap type of HRM to malfunction.

Here I am wearing the HRM on the forearm: Purple-103_3-18-49_tb14edit

You can see it there on my left forearm, the Garmin 910XT is mounted to the tops of the handlebars.

My experience with this HRM has been largely positive but not perfect. As far as the immediate problems I was trying to solve; inaccurate readings and dropping out, those problems went away when I started using this product in place of the Garmin HRM strap. Additionally, placing the strap on the arm is far more comfortable than around the chest. It is also much easier to adjust something around the arm than it is when it is under your shirt. It isn’t just more comfortable because it is in a more accessible area, the strap itself is made of a softer material.

There are a few things to keep in mind with this product. Many triathletes will put their tri kit on (uni style or top and bottom) with the chest strap zipped into place and then they put a wetsuit on over the whole kit. You cannot do this with the Scosche since it would be difficult to get in and out of the wetsuit with this product on. The Scosche is 1 meter water resistant, which is plenty, but even in a non-wetsuit swim I wouldn’t wear it on the arm for the swim. When I did Boulder 70.3, I put the Scosche in my tri top pocket for the swim, during T1 I removed it and slid it into place.

This unit is ANT+ and simultaneously bluetooth enabled. There is no switch for one or the other, the result is that the little thing is power hungry. Scosche says you will get 8 hours of battery out of it, I ran it for 8.5 hours without issue so their claims are either accurate to conservative. I suspect the battery life would be worse if you were collecting data by bluetooth as well as ANT+ instead of just ANT+. This capability, while battery draining, will allow you to connect the HRM to popular iPhone and Android apps and other devices which don’t support ANT+. I don’t use any of those, people that use things like MyFitnessPal and similar apps can sync their heart rate to the phone and and fitness watch at the same time.

I did encounter a problem early on which caused me to RMA the unit for a new one. The calorie and training effect metrics which display in Garmin Connect showed things which were way off. image

Here is the data from my Garmin from the bike leg of my 70.3, notice something off? I am a decent athlete but after two hours and forty minutes I can promise that I would have burned more calories than 90. I originally opened a ticket with Garmin who directed me to Scosche. Apparently the first revision of the software the units were shipped with used a defective calculation for Calories and Training Effect, as a result Garmin simply calculated the caloric burn as if I was at rest. I got a new unit and it works better, though the training effect still seems to be off.

It is unclear how this would effect a user who was not using a Garmin device, most people mentioning issues are Garmin owners so it may be that this was limited to Garmin and other users would not notice an issue with this at all.

I have one additional concern and that is the nice arm strap itself. It works as a sweat band similar to the bands that basketball players use to keep their hands free of the sweat from the upper arm. This means the strap gets soaked in salty sweat during every workout. I haven’t seen evidence of the material starting to fail or lose consistency but it is something I am going to watch.

Overall I like the transition from the chest strap to the arm band. HR readings are essentially accurate, pairing is easy and reliable, and re-charging the thing is not difficult. It isn’t perfect, no device is, but this is pretty darned good. I am comfortable recommending the product to anyone willing to spend $80 and hate chest straps.


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