Training in the heat? TSS?

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  • #54104


    Just wondering if anyone has thought or done anything by means of adjusting training stress to account for extremely high temp/humidity. I expect it may be too difficult to apply consistent fudge factors to TSS but just wondering if anyone has thought about this?

    I live in Hong Kong where the summer months (May->Sep) are regularly upwards of 30C (max out around 38C) and 70-80% humidity and I find the training stress to feel significantly larger than just the increased HR would account for. Last Saturday on my long run it was 33C and 75% humidity. That gives a wet bulb temp of just over 29C (or ~84F). If you then add direct strong sunshine on top it can be pretty brutal (a cloudy day under the same temperature/humidity feels nice by comparison). The volume of sweat is enormous and I find I definitely have to be on top of electrolytes.

    Not sure how you would quantify this or if it really is actually a larger stress and its not just my mind :). It also definitely gets “easier” as your body adapts by increasing sweat volume, reduces salt concentration of sweat and seems to trigger sweating much more quickly. Even after those adaptations I still think I could do the same run in more normal temps and the TSS I get at the end might not be too much different but my body would feel a lot better and recovery would be a lot quicker.

    From other personal experience I think it could be the humidity that really makes it tough because I think running in very hot but dry temps is a lot more bearable because at least your sweat actually evaporates 🙂

    Interested in others thoughts or experiences.



  • Participant
    LindsayTroy on #54112

    I totally agree with you about feeling worse in the heat, but that said, my HR is definitely higher when I work out in the heat for the same activity. Sometimes 10-20 beats more for the same pace. Which would be borne out in the TSS, does this not occur for you?

    From other personal experience I think it could be the humidity that really makes it tough because I think running in very hot but dry temps is a lot more bearable because at least your sweat actually evaporates ?

    As a person who is from a swamp but now lives in a desert, I feel the opposite. The dry heat dehydrates me so quickly.

    dan.k on #54154

    Hi Lindsay,

    Thanks for your reply. Yes, I also see moderately increased HR but I just feel that the TSS number that comes out at the end does not reflect the stress that I feel (i.e. hrTSS is higher because HR was slightly higher but I don’t feel like the difference is enough). This could all be psychological though 🙂 It could also be that due to sheer volume of sweat that on some of these occasions I was impacting electrolyte levels that would also make me feel like recovery was harder.

    Interesting that you feel like dry heat is better. I find that with dry heat the sweat at least does something…(i.e. evaporates and cools you) but with the heat and humidity my body pumps out huge volumes of sweat (and sweat volume definitely goes up after a couple of weeks of the summer) but unless there is a decent breeze it really doesn’t feel like it cools you down much. I get home looking like I have been standing fully clothed in the shower. I remember once I drank over 6 litres of water during a long session one day and still lost 4kg in weight.

    I should say that I have not consistently spent time in a dry heat location to be able to truly compare but I just feel like when I go somewhere like that in the short-term I find it a lot easier than the humidity. I think that in dry heat it might be harder to notice you are losing so much moisture though because it does all evaporate (and cools you) so perhaps making it easier, as you say, to get more dehydrated.



    Anonymous on #54195

    @dan-kefford: I’ve had the same experience. After 45+ years in a dry climate, I’m now in a humid one and hating it.

    I think the additional stress is both physical and mental, but I don’t think it qualifies as training stress (unless the goal event is also in a hot, humid environment.) Heart rate is primarily a stress measurement, and training intensity is only one component of the whole. Heat and humidity would be two, large, additional factors.

    I’m not sure how to adjust TSS for heat and humidity or if it should be. As Lindsay said, your HR for a given pace is likely higher, so hrTSS will also be higher.

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