Revision as of 18:11, 20 April 2017

There are two main problems with Heart Rate Monitoring; poor accuracy and chaffing, and there are two simple fixes. The first fix is to apply a littleBuh-Bump Electrode Cream, which improves the accuracy and provides some lubrication that reduces chaffing. The other fix is to apply some duct tape to the bottom edge of the strap, which works wonders at preventing chaffing. I had no chaffing problems with a duct taped strap during the 37 hours I was running Badwater. There are other issues, including the strap wearing out, which are covered below.

Buh-Bump and Duct Tape can fix your Heart Rate Monitoring woes.

Apply the duct tape to the lower edge of the back side of the strap. Don't cover the electrodes or you won't get a signal, but you'll need the tape to be on the lower edge to get good adhesion. You will need a strip of duct tape about an inch wide.

Fold the duct tape up over the front of the strap. You can stick it to the transmitter as shown in this picture, which gives it good adhesion.

1 Other Fixes

There are a number of problems you can still get with the Heart Rate Monitoring.

• Unlike the Polar system, the contacts on the Garmin transmitter tend to rust, so it's important to disconnect the transmitter from the strap after each use. You can see a little of the rust in the picture above.
• If you do get rust on the transmitter connecters, then a wire brush can fix the problem. I used these small brushes that worked well for me.
• A low battery can result in bad reception, and the watch does not always report a low battery condition properly.
• When replacing the battery, insert the new one upside down for a few minutes to short out the contacts. This will reset the monitor and may prevent some reception problems. (I've had to do this with both Garmin and Polar systems.)
• A factory (master) reset of the watch may be required. I found this fixed a number of problems with my 310XT, including heart rate monitoring.
• The straps can be damaged by washing and require careful hand washing, not machine washing. If you damage a strap, it needs replacement.
• Interference from overhead power lines used to be a problem, but the modern systems have reduced this dramatically.
• All of the soft straps require periodic replacement, so you may need a new one.

2 Garmin's HRM4

Garmin has introduced an updated form factor for their heart rate monitors which makes them much less likely to chafe. I upgraded to the "HRM4", and it's greatly reduced my issues.

The HRM4 at the top, the older style Garmin HRM, and the Polar H7.

3 Testing a Heart Rate Monitor Strap

Based on some empirical testing, I've found that the resistance between the popper contacts and the electrode pads is typically about 1.0-1.2 KΩ. A higher resistance suggests that the strap is worn out or damage and faulty readings are more likely.

Test the resistance between the contact for the HRM transmitter (the popper) and the electrode that touches your chest.

Here's another look at the two places to test.

4 Using the Polar Wearlink Strap

You can get a fabric Polar Wearlink Replacement Strap that works nicely with the Garmin transmitter. However, Polar replaced the Wearlink strap with the Wearlink+, so the original design is hard to come by. (The new Wearlink+ is nearly identical to the Garmin strap and not worth the upgrade.)

• Heart Rate Monitor Straps
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  The Polar and Garmin Heart Rate Transmitters, showing the similarity in connectors.

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  The Polar and Garmin straps, along with the Garmin transmitter. The older Garmin strap has the connectors on the end, and is even worse than the latest Garmin strap.

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  The back of the various straps. You can see the Polar has absorbent electrodes that work remarkably well, where the Garmin straps use a hard plastic electrode. The Polar strap is also more comfortable than either of the Garmin straps.

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  The Wearlink+ Polar strap has plastic surrounding the attachment clip that stops the Garmin transmitter clicking in place fully. Simply trim off the extra plastic with scissors and the Garmin will connect solidly. This picture shows the excess partly removed.

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  At the top you can see the newer Wearlink+ and the older Wearlink on the bottom. The Wearlink has pads that are absorbent so you don't have a problem with them drying out, but the Wearlink+ seems to be slightly more reliable.