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Crazy HR data

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  • Crazy HR data

    Hi - I'm a long-time Garmin user with (currently) a Forerunner 405 and an Edge 705 to my name. I'm currently marathon training so have started to try and use my HR to monitor progress and help me with managing my effort and pace. The thing is, it's gone NUTS! I'm 47, so using 220-age my max should be something around 175 - I reckon, from looking at 3 years worth of data it's actually about 185 on a really hard session - but recently both FR and Edge have been giving really, really high readings.

    Today I've just done 8m at my intended marathon pace or slightly quicker, with 1.5m warm down at the end. During my warm down my HRM said my AVERAGE HR was c225, and did in fact hit 253! This just cannot be right.

    I know Garmin HRMs have had a bit of a reputation for spiking at the start of an activity, but this was right at the end. The average for the session was 199, which is a level I've never seen in 3 years of running and cycling.

    The battery is new, so it's not that - do HR straps "wear out"?



  • #2
    With the hard strap (HRM1, 1B, or 1G) the most common cause of the strap suddenly reporting a lot higher heart rate is that sweat got inside of the strap and it's interfering with the amplifier circuitry. If you open the battery door and you see any green or white crusty stuff around the battery, or rust on the battery terminal or contacts, then that's a symptom of sweat or water ingress.

    This can happen because the battery door wasn't properly secured, if the O-ring in the battery door opening was lost, or if the plastic case of the HRM failed. They sometimes crack along the weld line, or from the edge of the battery door where the lot code is stamped.

    If any of these things is evident then there is not much that can be done other than to replace the strap, because it's very hard to clean the electronics without opening the strap (flushing with rubbing alcohol can work but is not 100% guaranteed) and if the case is cracked, it's difficult to seal it successfully.

    One other thing you should make sure of, if you have the battery door open, is that the positive battery contact isn't stuck between the case halves. You should be able to lightly pull it inward from the edge of the battery compartment and it should then rest against a post molded into the case back.


    • #3
      Genius! Thanks - that's the problem. The battery's even got rusty bits on after 3 days and there's green stuff on the contacts. I've got an old one that I'll try and if that's no good I'll get another. Are the newer ones less susceptible to this?


      • #4
        For the hard strap, the plastic design has had some minor improvements, mostly related to the battery door, over the last couple of years. The build quality is tested and audited to make sure defects don't creep in, so it's very unlikely that you'd get a leaking unit out of the box.

        The soft straps are more comfortable to wear but they require more regular maintenance (washing, possible cleaning and lubrication of the snap contacts) than the hard strap, and it costs more... so if you're happy with the comfort and function of the hard strap then a new HRM1G would work fine for you and it's compatible with both the ForeRunner 405 and Edge 705.

        But if your old strap works for you, then you could just use that too. If you do have to replace its battery, just make sure you don't lose the O-ring around the battery door.