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  1. #1
    Gears, beers and slices..
    Reputation: Pizza_Royale's Avatar
    Join Date
    Feb 2008

    Help! Wonky HR readings on my FR 305

    I've got a Forerunner 305 with a wonky HR interface. Occasionally during a ride the HR reading will just start counting way down, hover there for a bit, then start working it's way back up.

    e.g. over a span of 10 seconds or so, and in the middle of a ride, I will occasionally see something like this happen.

    160 - 142 - 118 - 96 - 72 - 58 - 77 - 91 - 113 - 135 - 160

    It's done it since day one, and it's done it without any interference around. Any ideas? Does anyone think it's just a matter of changing the battery?

  2. #2
    Double-metric mtb man
    Reputation: Psycho Mike's Avatar
    Join Date
    Apr 2006
    Could be a weak battery....mine defaults to something like 50 bpm when the battery is just about dead. Could also be how you contact the strap and where you run it. Try the different battery and possibly move the strap to a slightly different position.
    As if four times wasn't enough-> Psycho Mike's 2013 Ride to Conquer Cancer Page

    Moran? Let your opinion be free -> F88me

  3. #3
    mtbr member
    Join Date
    Jun 2006
    I had a similar problem with my edge 305 with bogus readings all of the sudden. I thought it was a weak battery, but I either read in the manual or on their web page about different clothing that you wear while using and the affects of it on your heart rate strap causing static.

  4. #4
    Gears, beers and slices..
    Reputation: Pizza_Royale's Avatar
    Join Date
    Feb 2008
    Supposedly static from clothing will cause spiked readings, but I have not found any real explanation yet for low readings yet. I'll try the motionbased forum.

  5. #5
    trail rat
    Reputation: slocaus's Avatar
    Join Date
    Jul 2005
    You need gel.
    All HRMs have a chest strap that picks up the electrical signal from beating heart and transmits this information to the HRM. For the chest strap to 'hear' your heart, the contacts need to be wet. The common way to do this is apply some water or spit to the chest strap. Instead try a conductive gel the kind that physical therapists use when doing ultrasound. Several bike shops including Performance now sell the (marked-up) consumer version called Bah-Bump. I haven't used it yet, but it seems like a great way to maintain a contact between your body and the chest strap.

    Spectra Electrode Gel is the best deal.

    I'm 58 and had two stents placed in my heart 2.5 years ago (link in my sig). My cardiologist said no riding. I bought a HRM and rode anyway. To prove to him that I am doing OK, I took printouts but told him I was hiking.

    He approved once I showed him the charts, but he noticed little things in the chart that were not correct. Being a doctor, he asked me if I was using a conductivity gel, I said "no". He tossed me a tube of it, and said that if I was going to bring him data to support my riding, to use correct procedure to get the best data I could for him.

    Now I use gel, and he and I are both happy. It is the conductivity through the chest wall, not the HRM itself. Get some gel!
    "The physician heals, Nature makes well" - real fortune cookie

    CCCMB trail work for trail access - SLO, CA

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