Possible error HR readings on long runs

Towards the end of a 28 milerun I thought my HR readings were wrong. I had successfully kept readings to mid 130s or lower thanks to a walk/run approach. However, in the last few miles the readings went high & it took a good while to get them down.
Might this be due to a lack of food/carbs? I did take some food on board but maybe not enough soon enough.
So, does anyone know how I can tell if the readings are wrong?


  • how high? 10 beats more or 40?
  • Probably just that you were knackered ?

    HRMs dont normally read wrong - you may get spikes of 220 or so occasionally - but thats easy to spot.
  • candy - My late night post left out that important piece of info, sorry. It has gone from low 130s into mid 150s in a matter of seconds on the flat during the week. But yesterday towards the end it moved from high 130s up to 160+. It did take a while to come down though so I wasn't sure if I was knackered as cougie says. Although I didn't feel knackered it was the furthest I've run!
    Looking at the readings I see I managed 187 before 20 miles whereas my max is 183!
    I guess I should get more info before forming a conclusion just yet.
  • "I managed 187 before 20 miles whereas my max is 183"

  • I work on the theory that as long as my heart rate is above zero I'm doing fine.
  • I don't think it's the same as you're getting, but I have had jumps in my HR that have occured due to a poor contact, and it double reads some beats. Not helped in my case by a slightly eratic beat. Jumps from 140s to 180s. Cured in my case by tightening the strap a bit. Over the course of very long runs (2.5 hours+ then I was loosing enough fluids to make the belt a little loose, and then I got the dodgy readings.

    PMSL @ Dragon Breath. Great Mantra.
  • Jim - I sometimes get the same problem when I am dehydrating, my HRM is all over the place.

    Mind you, I have been told by cardio doc that I have an erratic heartbeat sometimes.
  • Jj - I know!

    Dragon Breath - yup, there's a good baseline for all of us. :)
    D74 - I tightened the belt after Friday's run in case it was a bit loose. I hadn't thought it might get loose on yesterday's run though.

    Muzzy - I'm wondering if lack of food or drink played a part, although I didn't feel dehydration was a problem during the run or later. Possibly I was heading that way?
    The celebration for you Muzzy is that the cardio doc confirms you have a heart (forumites please note!).
  • #anyonewhohadaheart

    and know that I lo-o-o-ove you...#

  • Cilla

    ... and I claim my £5.
  • assuming that you were out for 4-5 hours, you would expect some sort of cardia drift, probably in the range of 10-15 beats for the same effort (especially @ ~70-75%HR)

    if its more than that then it'll probably either be dehydration or lack of endurance..
  • Cartman - I was out for 6 hours (less a minute & a half!). The lack of endurance is a (frightening) possibility. It was the furthest I've ever run, & the longest time I've run (with walks). It's a little frightening cos I'm looking to cover 55 miles in 9 weeks time. Still, cardiac drift is bound to be in there. I just wondered if it was a lot of drift & therefore possibly error readings.
    Cheers for your thoughts though.
  • I'm not an ultra runner, the only thing I've got to compare it too is going on a 6hr bike ride and over that time (when working @70-75%HR) I'd expect to see at least 10BPM drift.

    Make sure you are drinking lots, (e.g. 750ml per hour ?).

    cardiac drift is not a problem per se, you just need to know its there and adjust your pace appropriately. For example if you have twice the distance to cover and you are already hitting 160 (87% ?) at half way, then its probably a good idea to slow down even more at the start. Either that or wait for your body to slow you down naturally later (this is probably gonna be painful!).

    all that said, if thats your first really long slow run, then over the next few you should see a pretty big improvment.
  • Cartman - I must admit, now I think about it, I only had 2 litres of fluid. It was a cold day, so when the warmer weather arrives I'm going to need plenty more. I want to keep the HR well below 160. Cheers for the positive about a big improvement. I've got 2 more long runs planned & then a cutback week, followed by 3 more long runs. I'm sure that on 'the day' it will still be a venture into the unknown.
  • Note the word 'Drift' in cardiac drift. It's a slow increase over time, not a 25-30 'jump'.
  • Talk about irony!!!

    The lack of endurance is a (frightening) possibility. After you have just run 28 miles!!!

  • I've seen cardiac drift lots of times on long runs - in my case up to 21 miles - but it's probably less than 10bpm increase over the duration.....

    the only time I've seen a sudden jump like JN describes was in a marathon at 21 miles when my energy levels plummeted (hit the wall) - slowing down, getting a gel and some proper fluid down my neck rather than just sipping, brought it back to a more normal level and I was able to pick it up again........
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