Heart rate v pace

I've spotted on my long runs that if I run to a steady heart rate, my pace (not unreasonably) drops off - especially after a dozen or so miles. I'm interested to know what the physiological reason is - is it to do with scraping the glycogen barrel, or deterioration of my running style (& efficiency), or dehydration, or what? And in a marathon, is it better to maintain a steady pace (as I'm given to believe) or constant HR (does this equate to constant effort?)? I don't intend to race with an HRM, by the way, just train.

Thanks, you lovely lot.


  • Dunno about you Swerve, but I just get tired...

    ... however, I'd still like to know the answer :-)
  • Ah. I KNEW there was a scientific explanation, RHW!

  • I think it is called cardiac drift, as you become dehydrated yor blood thickens so your hert rate goes up for the same exertion just to get the same blood volume per stroke.
  • As you continue running the energy sources change their mix using more fat the longer you run. The oxygen cost of fat burning for the same amount of energy is higher. You need more oxygen to keep going at the same rate, therefore a higher heart rate.

    Dehydration can only account for a very small amount of drift. Only 2% dehydration will cause a dramatic collapse in the ability to keep running.

    The time it takes to turn on fat burning and the need to preserve carb stores in a marathon is the best physiological argument for negative splitting a marathon. Noticing drift demonstrates the change in the energy mix.

    This comment is derived from data in Noakes - Lore of Running (4th edition - waiting for a birthday to get the 5th!), http://www.pponline.co.uk/encyc/0690.htm and personal experience.

  • NessieNessie ✭✭✭
    Big Wayne's link is to a crappy war game site. B***** all to do with running.

  • seems to be a troll nessie.
  • NessieNessie ✭✭✭
    Where did the phrase "troll" come from. I sort of know what it means in the context of the forum, i.e. someone who claims to be someone or something he isn't, nut why "troll" (as opposed to say "sneaky bugger")
  • internet troll

    "a troll is a person who posts messages that create controversy or an angry response without adding content to the discussion, often intentionally"

    doesn't seem quite right in this case.. but the latter part seems to fit nicely.
  • NessieNessie ✭✭✭
    Ahh, thanks for that. I had (as seems to be normal) assumed it was from the mythical creature. Although some of them..........
  • i'm sure the origins are along those lines somewhere nessie.. i mean... what are mythical trolls good for ?
  • NessieNessie ✭✭✭
    Eating Billy Goats, I believe. :-)
  • Thanks, people, especially Ye Hippo and Milamber. And finding out about trolls was a nice bonus!
  • NessieNessie ✭✭✭
    Sorry for hijacking your thread, but at least we waited until the original question was answered (this time) :-)

    Actually, the question was one I wondered about for ages too.
  • No problem, Nessie!

    Actually, I seem to be trolling you - how's the training going?
  • NessieNessie ✭✭✭
    No, I think that's called "stalking" ;-)

    Training is not too bad - the orthotics seem to be helping, and it's all starting to feel good again, not just hard work. As soon as these exams are out of the way, I'll be a training animal and knock loads of time off all of my PBs.

    Nice dream anyway!
  • Glad it's coming along well. Mine too. Cranking up the miles nicely. And I've got the Loch Ness route profile as my PC wallpaper so I can memorise the tough hills. This may indicate mental disturbance of some kind.

    Exams bad. But then, if you will be an accountant...... ;-)

    Stalking - yes! That's the word!
  • excuse me whilst i extracate myself from this discussion.. *click*
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