Suspicious difference in indoor/outdoor heart rate

OK, so I understand there will always be a difference between indoor and outdoor, but 10 beats per minute?

I tend to feel that workouts are easier outdoors, and now I have some good data to back it up. 13 days ago I did 4 x 8 minutes @ 100 % FTP (Mount Regan) outdoors, and it felt only moderately hard. Over the final four minutes of the last interval, I averaged 273 W and 167 bpm. Today I did the same workout indoors and got 271 W and 177 bpm. It felt much harder.

Outside I use an Assioma Uno power pedal, while inside I rely on the Tacx Neo 2T. When I compared these 9 days ago (Zwift Power - Login), I found that they are within 2% of each other at about FTP.

I realize there are many variables, e.g. the outside ride was in week 1 of my autumn program, while today is in week 3. But I feel well and rested, and like I said, this is not the first time I feel that outside workouts are easier. Also, the temperature outside was only 11 C. But I have a decent fan indoors, and I didn’t feel overheated today.

I’m wondering if the power pedal is to blame. It’s supposed to have accurate temperature compensation between -10 and 60 C, but what about sudden changes, i.e. if I take the bike out of the house to ride?

I don’t always calibrate the pedal before each ride, but when I do, it almost always comes back with the number 0, which makes me think it doesn’t really vary from day to day.

Anything else to consider? Is 10 bpm normal, or is there something wrong here?

I can’t help but feel that now it will make a substantial difference whether I do a workout indoor or outdoor. And the adaptive training is going to be a bit pointless if the perceived effort is just going to depend on where I did the workout.

What was the room temp vs outside ?

When you are outside, there are a ton more variables than inside.
Plus usually, riding outdoors, you make more power (or at least that seems to be my expirience)

Outside was 11 C, inside was normal room temp, so probably a little over 20 C. And like I said, the pedal is supposed to be able to compensate properly for the temperature. Of course, my body will not have to work as hard in order to cool me down, but is that enough to explain the 10 bpm difference?

Not much wind, and the intervals where uphill anyway. And the power was roughly the same, and also relatively stable.

Temperature seems to be different. That could account for some (not all) of it.


Maybe I’m just not savvy enough to understand this, but how does zwift power allow you to compare two power meters to understand their offset?

Also, 2% might be enough difference at 100% of FTP. Doing 10 minutes at 100% is potentially significantly different than 10 minutes at 102% if your FTP is even slightly overestimated.

I haven’t trained indoors since around April/May. I failed the first hard workout I tried which I’ve previously completed (VO2). On a low endurance effort my HR is 7-10bpm higher indoors than outside (<140bpm outside, 145-150bpm indoors). If you haven’t trained and gotten used to indoors riding in the last few weeks it will take you some time to get back into it. Even if you have the combination of constantly having to push the pedals, heat, static riding position and other variables will make indoor riding different.

The “0” is probably just an indication that the calibration was successful. I get something similar with my crank 4iiii crank PM, only it returns a “10” for successful calibration. It’s really just a zero offset in reality rather than a calibration.

For me the difference between indoor and outdoor riding is cooling. I have a lasko fan, but even with that on full aimed at me, I still heat up more than I do outside when its anything under 85F.

Look at your body cooling setup. I currently run 3 lasko fans, 2 pointed toward my front and one at my back. With a single front fan previously I’d be dripping in sweat on SS, now I get off and only have light sweating as I get off.

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I have the same experience. When i do an FTP test i can do outdoor 310w for 20min, but indoor (with the same powermeter) i can do 295w. So difference in FTP outdoor 310x0.95= 295 vs 295x0.95=280. Do i need to change the FTP for indoor, or exept that the heartrate is higher with the problem that i failed in doing SST etc?

When you are riding inside you are just pedalling the bike, looking at blue bars on a screen telling you how hard you need to go…

Outside you balance the bike with your whole body, you are travelling at speed, you are vigilant of your surroundings, etc.

Its not weird to have a bit higher HR outside if you are used to just riding inside focusing on nothing but pedalling.

For me it’s a seasonal thing. When I have been riding the trainer a lot in winter and then come outside, it takes a few weeks for my outside HR to come down after riding indoors all winter.

TS saying that he have a higher HR indoor.

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Sorry, totally missed that detail.

In that case, I would look airflow, hydration, cadence…

Even though temperature might be the same, airflow has a huge impact in driving away heat. Even with 3 fans, I often feel cooler outside.

Its a big difference between feeling overheated, and how the body reacts to 11c vs inside temperature etc.

I have realsed that when I ride in 13-14c outside, with maybe a tad too little clothes on, my HR is at its lowest!

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