What on earth might cause a problem like this, that only strikes after an hour or more into a long run, and only after a month of use for the heart rate monitor?
When the first HRM started malfunctioning a couple of months ago, I tried cleaning the strap, tightening the strap, replacing the battery, and updating the firmware.
The Rand Mc Nally TND 730 is the forth generation of this GPS product.
It’s much more than a mapping device for a truck driver, it’s a comprehensive solution for a person who makes a living on the road.
In my tests, hand washing with soap in a sink of warm water didn’t help at all, and machine washing with other laundry (per Garmin’s instructions) only partially helped.
After washing, the problem returned again within a matter of days, if not sooner.
After lots more experimentation, I confirmed the problem is at least partly due to sweat and salt build-up in the strap fabric.
But I don’t think that’s the problem here, and I always use electrode gel anyway.The GPS element of the device features a highly user friendly interface that permits the input and alteration of mapping and destination data with ease.The 730 comes complete with the Rand Mc Nally Dock, a set of features designed from the bottom up by professional truck drivers.Sometimes it would jump up again to a normal-looking value, but more often it would continue decaying downward from around 150 all the way to the 40’s, and stay there until the end of my workout. An hour-long total decay, with eventual recovery: Partial decay at the end of a marathon, with some earlier gaps: Total and permanent decay at the end of a workout: This pattern of failure seems different from the types of HRM trouble I’m more familiar with, which involves bogus (usually too high rather than too low) pulse readings at the beginning of a workout.That problem is normally caused by poor electrical conductivity between the strap and the skin, and can be solved by wiping on some spit or electrode gel, or just waiting until the skin gets sweaty.
Or maybe the salt permanently damages the conductive threads in the fabric?