Yes it is very common that your outdoor FTP is higher than your indoor one. I believe the primary reason most people mention about this is the cooling effect of riding outside, but I’m sure there are plenty of other factors.
Just want to re-iterate the initial question, which is not so much debating whether there is a difference (there usually is, and it seems that the cause is usually cooling). Instead, the question is:
Given there is a difference in power output, is the training effect and subsequent fitness adaptation the same?
I think physiologically you’re working harder indoors, but also you are working much more consistently. For example it’d be very hard to get a 20 min SS session as accurate outdoors as it would be indoors.
Mine has always been about 10% off to the dot, and tbh, it really frustrates me that training software companies don’t support multiple profiles (useful for TT bikes as well). A solution would be to have an indoor profile (FTP, Curve, TSS), Outdoor, etc. Even my CX bike which has a Stages is off because its a terrible PM that reads high.
I’ll probably do about 6000 miles indoors and 6000 outdoors this year, so my TSS is almost always off in some form. Adding to that, I do about 2000 on the CX (my commuter) and about 500 on the TT (which I’m 5% off).
This all means my TSS is off by 5-10%, and I can’t just go off one FTP because my outdoor FTP is too hard for indoors and too easy if I flip it.
This all sounds like nitpicking but if I’m training for something specific I need to know what I can do; for example it would be nice if I can only see my TT numbers so I can get a real value to estimate off. Meeting in the middle also isn’t optimizing your training which is kind of what this is all about =]
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But take that to an extreme. For example, on the podcast, Nate and Jonathan were talking about training in a hot bathroom and only being able to complete short endurance rides. Sure, the physiological toll is high, but the training effect (if we’re talking improvements in FTP) is not the same as doing a similarly taxing ride at a higher power output. I think …
I’ve been trying to figure out why it is different for past 4yrs since i got a trainer. Mine is ATLEAST 10% lower on the trainer. I have P1’s so measuring device is same. I thought maybe it was temperature, but in playing with that it doesn’t seem to be issue. I agree. It’s a little frustrating in making sure you are working a hard enough. My HR is even a little lower on trainer. You could say I’m not working a hard enough, but my legs would disagree as they can’t go any harder with a 10% lower ftp setting on trainer.
After reading a lot about how your max running HR will be higher than max cycling HR because you incorporate more muscles in running, I wonder if this is why my ftp is lower on trainer. Indoors i feel like im only utilizing legs where outdoors I know my upper body is working. This would account for a little higher HR outdoors. And I’m currently feeling that my upper body has to contribute to some amount of watts, which I’d be missing inside. Maybe a rocker plate will be the next thing I try.
Does anyone else notice that the folks who seem to perform best on trainers are the sprinters or those good at short duration power? I often feel I lack enough torque to put out power on trainer even when I’m running 95+ cadence.
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Interesting thinking. My outdoor and indoor power is the same. I use my power meter as power source for both indoors and outdoors. I use a Kurt Kinetic Rock N Roll trainer. So my scenario further adds to your theory 
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I definitely agree with you guys that its not all heat; I’m out here in the desert and can put in solid numbers at any temp up to 106 degrees. Meanwhile I can have 2 fans and it be in the low 60’s in my house and struggle.
IMO, there’s a lot of ‘micro movement’ when riding outdoors that contribute to your power. A lot of movement with the arms, hips, etc go into it and its almost unnoticeable but its there. When you’re locked in on a trainer you lose that. Maybe rocker plates help, I’m not sure.
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I agree with the micro movements. And I think I actually move around a lot more than the avg person. I’m tempted to try a rocker plate, but I’m afraid it will allow the bike to sway, but won’t be like it would be outdoors. Maybe someone has switched to rocker plate and can confirm their power went up and can pipe in here.
I did a ramp test (dumb trainer, Stages) and got 247. Outside, 2x8, same Stages and got 220. About a week apart. Not sure what is real.
Ikr? Are we even real? 
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I thought my indoor and outdoor FTP was important at first. Not anymore. I just worry about the indoor FTP as that is where I do all of my testing and structured training. What does matter and is of the utmost importance, is that my outdoor rides are improving because of my indoor training, which they are. Trust the Ramp test. If you think it may be wrong calibrate your trainers and retest again on another day.
I’m just getting started with the structured training, finishing up with SSBMV II. I’m already looking forward to starting the 8 week block of Sustained Power Build
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This difference has been bugging me also for quite some time, and I have been annoyed for not being able to properly treat indoor and outdoor rides separately FTP-wise (TSS, PD-curve, time-in-zone etc). I can sustain 3-4 minutes indoors at my average ~15min (10k TT) power outside…
Recently I got access to a lactate meter, and decided to test the difference in lactates at various power levels, and the differences were quite substantial. Test were done with the same bike and power meter (Favero bePro) few days apart. 5min work intervals with ~30s pause for lactate measurement. Trainer used was Elite Direto.
Indoors (avg power, lactate): (165, 1.2), (191, 1.8), (216, 2.3), (242, 3.6), (267, 5.1)
Outdoors: (avg power, lactate): (166, 1.0), (195, 1.0), (220, 1.1), (245, 1.7), (267, 2.4), (280, 3.9)
I also don’t buy the heat/cooling being the biggest part in the difference. I have a decent fan indoors and the base temperature was actually way hotter during the outside test than inside, 25 celsius vs 18 celsius.
My theories for the potential causes for the difference are basically the same things that are already mentioned by others in this thread:
- Fixed bike indoors requires one to use smaller amount (or maybe even slightly different set?) of muscle fibers of your body to produce the power, which causes higher lactate levels at same power output. In other words, outside you can use more muscles (more of your whole body) to aid powering the pedals?
- Lower inertia on trainer (even on decent direct-drive trainer) requires one to apply force along larger portion of the pedal stroke compared to outside, again increasing muscle’s metabolic demands and thus increasing lactate production? In other words, outside you get more ‘micro-rest’ periods during the pedal stroke, which affects metabolism?
This is obviously just N=1 experiment and I should do it few times more to confirm the results, but I think this clearly shows that these activities should be treated with distinct FTP to be able to effectively follow the progress and prescribe workouts in them.
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Yes, as I have said earlier in this thread, my situation would add weight to this. My inside and outside FTP (although I have never done an outside FTP, I do race) are about the same. My power curve is a good mix of inside and outside. My trainer is the Kurt Kinetic Rock n Roll, so my bike isn’t static and moves very much like it is outside.
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Anecdote, because n=1 is not data…
My indoor FTP and outdoor FTP correlate pretty well if I use eMotion rollers indoors. If I switch to a dumb trainer it’s definitely harder to hold threshold or do 4x8 type work. HR and RPE both go up.
Could be mental and can’t do a blinded test set. But suspect it’s being locked into a rigid position on the dumb trainer or how the resistance is applied which has some effect that is real but cause not clear.
Fwiw…
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very interesting. Post your result from your next test, thanks.
It’s all in one’s head. There is no indoor ftp vs outdoor ftp. There is only ftp.
https://journals.humankinetics.com/view/journals/ijspp/14/9/article-p1273.xml?rskey=YdsvTf&result=7
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It’s been well established that gearing on the kickr makes a noticeable difference.
But what about my Neo 2? Does gearing also affect the power output on the tacx?
Do you think you could put a value on how much harder it is on the dumb trainer? Unlike some people using a Rock ‘n’ Roll 2, I don’t like mine very much. It feels inconsistent especially at threshold and above. I should try a trainer tire and a bigger fly wheel but I’m not convinced it’s going to get me there, I think it’s the fluid system they use. I’m pretty interested in resistance based rollers and wonder if that could help me bridge the gap (it’s a big one typically) of my outdoor v. indoor FTP.
One study of 20 cyclists proves this?
All,
The way I’m currently thinking about FTP is that if I have a large block of indoor work on the calendar, I test inside. If I have a large block of outdoor work, I test outside. That makes the most sense to me instead of being so focused on the different numbers, this mindset should allow me to set up proper training zones. Am I missing anything?
Last, I understand why TR pushes indoor work so much, but isn’t there a TON of value working outdoors when it’s available? To the end that there’s even more value in outdoor workouts than indoors especially when we start to near A races? Skills, dealing with outdoor factors, riding in groups… I get that it’s much easier to become distracted outside but it’s more satisfying to me to get the work done outside. probably because I’m one that can hit much bigger numbers outside. Also, hills help me a lot. I know there’s a lot to that last sentence.
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Hesitate to make a guess as it would be just a guess. Also considering the sensation might be mental and not physical.
For me, I think it’s not being looked into a single position on the rollers vs fixed trainer. Would be fun to compare fixed trainer on a rocker plate vs the eMotion rollers. But too lazy to build a rocker just for the experiment!!
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