The relationship between heat and power?

We had a spike in temperature today and I noticed that my heart rate was higher in relation to the amount of power I was putting out at the time. For example, my heart rate at 200W is usually around 135 but today in the heat I had to stay around 175W for the same heart rate. I understand that this is to be expected because the body has to work to cool it off and put out power at the same time. My question has to do with the impact on training quality.

Because I have to lower my Watts to stay in my Zone 2 heart rate parameters does it reduce the amount of training stress I’m putting on my body from a cycling stand point? In other words, am I getting less out of my endurance ride because I’m doing it at 175W instead of my regular 200W or is heat stress and training stress similar enough that my body will adapt the same way. I hope this makes sense. It’s is just something I was pondering during my ride and hoping you guys might have the answer.


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Heat stress is for real and unfortunately is underrepresented by power-based training metrics. You are pedaling lower watts but that’s because your body is dealing with the heat stress.

For example - I can do a 2 hour ride in Zone 2 in 95 degrees and feel absolutely wrecked. Relegated to the couch the rest of the day.

Conversely at 70 degrees that ride is delightful, don’t feel wrecked and power is better. And MOST of all you are recovered to train meaningful the next day.

So yes, heat absolutely impacts the quality of training. And if you live in a climate where you can avoid it, I HIGHLY recommend it. This is another reason why the seven habits of masters cyclists is riding in the morning when it is cooler:

For my southern athletes, like AZ, NM, TX, LA, MS, AL, FL, etc… we’ll go so far as to train in a climate controlled air conditioned room at 65-68 in the summer as opposed to 98 degrees outdoors. Isn’t as enjoyable but makes a HUGE Difference.

I may finally try this with a small portable ac unit. The balance between realistic sleep is severely if not obliterated by the early morning heat down here in the summer.

Since March my schedule has been open and for the first time ever I’ve been able to be consistent. So far reaching all time PR’s for basically every metric since using power back to 2007. Kinda sad if you think about it but, I digress… My wife and I would sleep in and wake up naturally about 7:30 each morning just after the last vivid dream cycle. Never and I mean never before had I experienced this. I understood what was happening and now that the heat is building I’m cutting sleep short to get out while it’s “cool”. Predictably, I’m not going so well anymore.

Anywho…I’ve never really thought about a portable ac unit so thanks for the reminder!