Does training in hot conditions change substrate utilisation?

do you use more fat or carbs at relative intensities? or the same at normal temperatures. RPE and HR are certainly higher but not sure if this influences carbohydrate reliance

More carbs.

But exogenous CHO is not metabolized as much - meaning you should go into the ride topped up.
https://journals.physiology.org/doi/full/10.1152/japplphysiol.00482.2001

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The main adaptations are related to your bodies ability to regulate heat, and increased plasma volume:

Here is the article: https://www.researchgate.net/publication/275954405_Adaptations_and_mechanisms_of_human_heat_acclimation_Applications_for_competitive_athletes_and_sports

the muscle metabolism stuff is at bottom of page 25 and top of page 26. My read - at best there are minimal adaptations related to substrate utilization. Someone else may get more out of it.

The OP asked about acute responses.

I thought it was ambiguous :man_shrugging:

They referred to higher HR and RPE, so acute.

why did you answer more carbs? I’ve got two handfuls of articles and journal articles, don’t recall a single one calling out the need for more carbs when training in the heat (either the first couple days, or after acclimatization). Curious because I deal with pretty dramatic swings in temperature. This morning it was 63F, this afternoon it will be 99F, and tonight there is a strong ocean breeze and I could be working out closer to sunset at 75F. During Spring/Summer/Fall it is not unusual to acclimate, then lose it, and then go back thru another round of acclimatization.

From one of the world’s most well-known sports nutritionists:

“Carbohydrate (CHO) requirements for exercise are increased in the heat, due to a shift in substrate utilization towards CHO oxidation. Daily food patterns should focus on replacing glycogen stores after exercise, and competition strategies should include activities to enhance CHO availability, such as CHO loading for endurance events, pre-event CHO intake, and intake of sports drinks in events lasting longer than 60 min.”

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thanks, I’m glad I asked. really cooked on a ride today so pasta party tonight :partying_face:

This was interesting because it includes a sample of studies done over the years:

That was interesting, and recommended a slight reduction in carbs during a hot ride.

In summary:

  • focus on hydration during a ride
  • slightly reduce carb intake during a ride
  • possibly due to reduced blood flow, you’ll use a bit more muscle glycogen during a hot ride versus cooler weather. That may or may not impact post-ride dietary carb intake.
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