Treadmill or outdoor run in high humidity conditions? | 80/20 Endurance

Treadmill or outdoor run in high humidity conditions?

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  • #17054

    Unfortunately I have to travel for work during the peak training week of my Level 1 Marathon plan. I will be in Houston (rather than in the UK) for 10 days, during which I will need to complete:

    RF28 – 55 mins
    RF29 – 60 mins
    R5K1 – 50 mins approx.
    RF28 – 55 mins
    RL35 – 31km

    The following week is recovery and I’ll leave on Thursday evening, but not so worried about those. My question is: this will be a huge change in heat/humidity (currently 15C here, will be 35C there). Though completing some runs in hot and humid conditions may be beneficial, I suspect attempting the long run will not be a great idea. How should I approach this?

    I wondered whether I should aim to do the shorter runs outside, and do RL35 on a treadmill. Are there any drawbacks to doing the longest run of the training cycle on a treadmill? Other than being on a treadmill for nearly three hours… I would much rather be outside but feel like I might not be able to maintain Z2 for 31km, and don’t want to cap the run out at 3 hours. Feels like there would be a psychological benefit to doing the full 31km.

    Keen to hear some thoughts!


    • This topic was modified 1 month, 3 weeks ago by James.

    I’m from Fort Worth, TX and have family in Houston. That’s actually where my dad grew up. It can be rough! I’m sure you’ll get different opinions here, but I would personally run outside. 35C (95F) is not an ideal running temperature and can potentially be dangerous. But keep in mind that this would only be at the hottest part of the day. If there’s any way you could do your running early in the morning, you’d still have the humidity, but the temperatures wouldn’t be nearly as bad. Probably closer to 75F (23-24C). Our temperatures are about the same as Houston and I do almost all of my summer running early in the day.

    Because it would still be warmer than you’re used to, I would suggest using some kind of running pace adjustment calculator like this:

    It’s under the advanced features. You would just need to pay careful attention to your hydration. I would use some kind of electrolyte tablets or fuel as well. That’s just me. I’ll be curious to hear other responses.


    Thanks Alan, this is really helpful. Definitely will be aiming to get out early in the morning, and paying attention to hydration. Looks like I might be able to run along the Buffalo Bayou for most of it, so at least it would be green!

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