Hi all,
I’ve noticed that in the last couple of months I’ve started to sweat more during my workouts. I thought it was the weather getting warmer, but I realized that all my workouts are indoor before it heats up; average temperature in my house is about 65-70F during my workouts.
Is it possible that since my power output has been going up that I’m generating more heat and, therefore, sweating more?
It could be a combination of a couple things.
As it warms up outside it usually gets more humid and higher humidity leads to worse evaporative cooling so you would sweat more.
Second, as you do more exercise your body will get better at cooling itself so you will tend to sweat more and sweat earlier regardless of power output.
And finally, yes, as you put out more watts your body is still working at approximately the same ~25% efficiency. So as your power output grows (the 25%) so does your heat waste (most of the remaining 75%).
And duration matters. Even if I’m pushing zone 2, if I am riding longer, I’m making puddles.
Yes, this is a factor.
Also, training in general leads to more sweat production, as the body seeks to control core temperature. That is also a larger difference that comes from specific heat training.
In my case, I’ve attributed it to increased humidity. Winters here are incredibly dry, but summers humid (though we are far from summer!). I’ve noticed in last 2 weeks that I will start sweating profusely even during easy 60-65% intervals, which I never used to. It may be due to other factors as well, but I suspect humidity is a major contributor.
Yes.
All else equal, more watts equals more heat.
The body’s efficiency of transforming stored energy into energy at the pedals is roughly 25%, and it doesn’t change much with training. The remaining 75% must go somewhere, and it’s largely going to be in the form of heat energy.
Fun lecture I watched just a few days ago. Some interesting graphs with watts vs temp at different humidity and sweat-rates required to cool (data is for runners, but whatever- the principle holds). Also some info on kit and how that can aid or hinder your evaporative cooling.
Yes, power output, but in my experience other factors also matter. For example, yesterday I was doing a pretty light workout if you just look at the IF. But it was low-cadence work (at about 60-63 rpm), and I was sweating a lot more. Also my heart rate was about 10 bpm higher than usual.
Weird, I can drop HR by dropping cadence from 80s to 70s to 60s.
I don’t quite understand it myself: on the road bike, my preferred cadence is in the 95-105 rpm range. On the mountain bike, it is about 70-85 rpm. 
You get more feedback witch is critical on the mtb, + higher cadence would make it challenging to stabilize yourself when the ground isn’t smooth. On the road bike, when the road is rough it’s usually nicer to drop the cadence a bit.
Like others have said, generally lower cadence = a drop in HR