Thread by @Scienceofsport

#Doha2019 World Champs starts tonight! Our NEW podcast sets the scene with a focus on the physiology & impact of the heat, & other likely themes (doping, stars, races to watch): podcasts.apple.com/za/podcast/the… Available on all major pod platforms. We’ll do event analysis next week!

Speaking of podcast, here’s a little ‘aperitif’ of our podcast discussion. Right now, in Doha, these are the conditions. The women’s marathon starts at 11.59pm in Doha. So 32C, very little wind, humidity 74%, feels like 42C. Terrific fun…performance-wise, here’s some thoughts...

Running produces heat - the body allows heat storage, and our temp climbs from resting 37C into the 39s, approaching 40C. Eventually though, a critical hyperthermia is reached. In lab studies, it’s at about 40C. Elites in races can probably go higher. But eventually, ‘lights out'

How quickly this happens depends on a few things:
1. How fast you run - fast = hotter
2. How heavy you are (bigger gets hotter)
3. The environment, which determines how much of the produced heat we can lose.
Two ways to lose heat - convection (air) and evaporation (sweat)

Convection happens when the skin is hotter than the air. Then the gradient is “skin to air”, heat is lost. Trouble is, once the air temp gets to 35ish, the gradient is reversed, so you gain heat from the air. In Doha tonight, at 32C, there’s minimal cooling capacity.

So now you’re left with sweat. Trouble is, when it’s humid, sweat doesn’t evaporate as much, so that avenue is limited. Hence, that combo - hot and humid - means tiny heat loss capacity. Now remember the three things determining body temperature - all that’s left is to run slower

But, because of lack of adaptation, anticipation & preparation, many won’t respect just how much they need to slow down, so the #Doha2019 marathons will be great demos of physiological blowouts. They’ll also be won by smaller athletes, all things being equal. But in SLOW times

Size matters hugely in the heat. Here’s a demo, based on heat storage models, for how two athletes, one 60kg and one 70kg, have performance limits 8 min apart on only mildly warm days. Doha will be worse. Many athletes will ‘melt’, small conservative ones to thrive.

For more on that (and a lot more!) give our latest podcast a listen:

podcasts.apple.com/za/podcast/the…

play.acast.com/s/realscienceo…

Last thought - wouldn’t surprise me if the top runners (and it’s a strong women’s field - 5 sub-2:20 athletes) hit halfway in 1:19-1:20, and only 5 break 2:35. Many will simply stop the moment they’re out of contention (why suffer for a 2:52?), so medical dramas may be avoided