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Heart rate during TT - big difference indoors vs outdoors

Wallace and GromitWallace and Gromit Posts: 1,561
Caveat - I know heart rates aren't the most meaningful data in the world, but they are still of interest.

When I do 60 minute TTs on the turbo, I generally see a signficant rise over the first 10 minutes or so, then a period of stability (20 mins or so) in the mid 130s range, after which the rate rises steadily to the high 150s / low 160s range by the end. All of this for broadly constant speed (as measured by a cheapo speedo on the back wheel).

I've started doing TTs on the road recently due to a flirtation with triathlon, and noticed on Sunday during a 40k effort in an Olympic distance event that after the rate had settled (following the wetsuit exit and run through transition in cleats) in the low 140s where it stayed for the whole ride (other than rising a bit during a headwind section) which was very even paced. I've noticed similar patterns in training as well, though my training TT route has lots of junctions and a few bridges so heart rate is more variable.

So I was wondering why this difference happens. Is it due to dehydration on the turbo whereas on the road dehydration is much less of a factor? Or would it be due to not pushing as hard in the triathlon ride due to saving a bit for the run? (I wasn't much slower on the bike than I would be in a standalone TT, which proved a bit of a mistake during the run!)

Or something else? (Overtaking lots of faster swimmers was a damned sight more fun than the turbo, that is for sure!)

Any thoughts would be much appreciated.


  • napoleondnapoleond Posts: 18,633
    There will always be a bit of you during the Tri saving something for the run (bear in mind you've just swum too.
    The wind has a cooling effect outside that you don't get even with a fan indoors, this may well lead to reduced HR for perceived exertion.
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  • fenixfenix Posts: 5,437
    I think NapD has it - its the cooling effect of outside. Your HR will rise if itis struggling with the heat.
  • ...bear in mind you've just swum too.

    I will never forget that swim as long as I live! Words cannot do justice to one's first open water triathlon swim!!
  • RutlandGavRutlandGav Posts: 144
    I think NapD has it - its the cooling effect of outside. Your HR will rise if itis struggling with the heat.


    Sweating, blood flow to skin to help shed heat faster while maintaining same flow to muscles - hr must go up.
  • Thanks for the comments. I've noticed the same rising HR effect when rowing on a static machine, running and cycling up long, alpine climbs. I'd just assumed that this was what my HR did, but on thinking about it, they are all efforts involving very little cooling due to low speeds or being stationary. Outdoor TTs are a new thing, and as I alluded to above, rather enjoyable in a triathlon when you're a lot better cyclist (though still pretty cr*p) than swimmer!
  • Strange because I notice the opposite. No trouble getting my HR up to around 175 when climbing outside. But inside I struggle to get above 150 even if my legs are screaming at me to stop.
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