Physiological gains - indoor v outdoor

I apologise if this has been asked before, but I’m interested in the benefit difference between training indoor vs outdoor based on the fact that the majority of people seem to have a higher outdoor FTP.

The ramp test gives me an FTP of 306; whereas I can manage 342w for 20 minutes outdoors; making my FTP around 325. (Supporting this FTP I can do 315w for an hour without too much difficulty).

I appreciate there are numerous reasons that may account for the gap in my performance ability eg hotter indoor, less ability to ‘move the bike around’ etc

Based on the above whenever I train outdoors eg TrainerRoad plans, I increase the percentage on the intervals by 5%. Yesterday for example, I did over / unders outdoors at approx 20w higher than I would have done them indoors presumably meaning that my body is having to produce 20 more watts for every interval and reaping the physiological changes as a result? On top of this I find the outdoor intervals easier (lower RPE, lower HR) than indoor, even though they are 5% higher in wattage!

I know my cardiovascular system may be working equally hard (or even harder indoors based on RPE and HR), but surely my muscles adaptation MUST be less indoors? On top of which I am practising a pedalling technique which is less applicable when converting to outdoor racing.

Thoughts much appreciated.


I’m interested in this as well. I did some sub-threshold testing yesterday. I wanted to know how many watts I was putting out at different percentages of HRmax. I ended up doing 3 x 10 minutes for a total of 50 minutes - all sub-threshold, all of which should have been pretty easy and not very taxing.

The intervals, of course, were not hard but my muscles were a little bit sore afterwards. My leg muscles were more sore than if I had rode 1.5 to 2 hours outside at similar intensities.

It made me curious whether the indoor trainer hits the muscles differently and/or causes different adaptations.

I’ve also only tested my FTP indoors because up until last week I didn’t have a power meter on the bike. The thing is I never train indoors. I wonder if my trainer tested FTP would be substantially higher if I actually rode the trainer more often. Of, conversely, when I get around to testing my FTP outside I gather it may be a lot higher.

Application of power (how you pedal) on a trainer is similar to climbing in that you better be good at applying force over the top and keep that force through a longer arc than not on a trainer or riding the flats.

Colby Pierce (Velo News) just did a great podcast about what happens if your position on the bike is too forward and high. While ok on the flats and not a trainer not so good climbing or riding a trainer. He didn’t specifically make the connection to trainer but, the inertia on a trainer is similar to climbing in that it requires a different pedaling technique to make the same power as outside if on the flats.

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Not sure if it’s really down to pedalling technique. I’m pretty good at climbing but my indoor/outdoor power difference is huge (~8%). Trainer definitely doesn’t feel like climbing.

Great question at any rate; something I’m wondering every time I get on the turbo and put out ridiculous watts with high perceived exertion.

I have the same issues. Another part you did not mention might be some loss in the drive train. Outdoors, I use pedal based PM’s and inside a direct drive Tacx. Not sure what your setup is of course.

But besides that, it feels a lot different outside vs. inside. Inside, for some reason my cadence is about 10 rpm higher during high intensive intervals >110rpm. Outside I do not mind putting in some spikes in power during intervals. It might be related to ERG that I use. Not sure but it seems the ramp test inside makes it harder for me in the last parts. Sustaining wattages above 400W feels so much harder inside than outside.

Curious about other thoughts.

I did test both PM’s together, to rule out differences in measurements. I see some watts more on the pedals than on the Tacx. And the Tacx responds faster to changes. But having a 3s avg makes the numbers pretty much the same.

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I don’t have a power meter for outside, so I cannot compare it based on numbers just on feel.
I ride ERG mode inside, usually in the same gear for all of my workouts.
For me it seems I get so used to the inertia/feeling of delivering power in that gear combination that that because the new normal.

When I get outside for the first ride after a couple of workouts indoor all other combinations feel odd, but that goes away once I start riding more outside.

I noticed the difference in cadence as well, but for me that’s down to gear choice, my cadence will differ on ERG mode as well depended on which gear I am in.
Not that I am specifically targeting that, but 100 RPM in one gear combination feels more ‘normal’ than 100 RPM in a different gear combination on the trainer for me.

I use the same PM indoor and outdoor. And yes, noticeably higher cadence indoors too - 85 vs 100 rpm!

Are you using Erg mode indoors? If so, what gear combination are you on? Which trainer are you using?

Yep, ERG mode indoors.

And yes, indoors I use small chain ring and 4th quickest sprocket, whereas outdoor I use large chainring and whichever sprocket…

Kickr 2018

Kickr 2017 direct drive, and after buying it October 2017 the first thing I did was play around in Zwift to figure out how to use it. Ended up with big chain ring for both testing and training as it delivered same RPE and FTP as outside. This seems to be a personal preference thing, maybe you’ve already evaluated both and settled on small chain ring.

I think you should test outdoors if you can, and if you have a block of outdoor training in the immediate future. Test inside when you have a block of indoor training. I use the same PM for both bikes and most of my work during this time of year is on the road bike and indoors. Still, I can definitely hit higher numbers outdoors, always could. I am noticing that my indoor power has improved, more importantly the duration I can drive larger numbers has increased. I think the TR thought is that your inside FTP and outside FTP should be very similar, or the same. I think of this based on my personal experience with cycling; 98% of all my training, up until last year was done outdoors. I would train inside only when completely necessary so I link part of the issue of matching indoor/outdoor FTP on what we have historically practiced. There’s something most of us face, it’s psychologically easier to go hard when you’re moving. I think it’s that simple. Now add in the huge issue of proper indoor cooling and you see a typical variance in outdoor v. indoor power numbers.

My goal this year is more closely match my outside number with my inside numbers, that’s an outcome I’d like to see. The path is indoor compliance which becomes much harder when good weather hits. I think training your indoor mental fortitude is important if you plan to spend any length of time riding inside.

Anecdote - I have never felt better than riding outside after a long block of indoor only riding. That first ride or workout outside makes me feel like it’s all worth it. And, like most of you I adjust the workout upwards a few %

I know this is a topic that’s been discussed a lot but it might warrant another look.

To be more clear, pedaling technique or more specifically, how a rider applies torque can be negatively affected if too far forward and/or too high in that with the lack of inertia on a trainer or climb, tangential force is less over the top.

For peeps like me who are fit more forward this might explain part of the difference between trainer and road, flat and climbing. It may very well not explain or be relevant to you or riders fit a little further back (all things equal).

Anywho, Colby Pierce explains it with Velonews much better than I. It was one of the gems that caught my attention as I’d never thought about it in this way.

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what was the podcast where he explains this?

Quite relevant:

Summary: Riding on a stationary trainer tends to produce higher RPE for the same effort, with implications on how long power can be sustained at any given intensity. This is probably caused by cooling most significantly.

Biomechanical muscle recruitment changes on a fixed platform trainer vs on rollers, treadmill, or road cycling. Trainer appears to encourage more quad-dominant force production and less accessory muscles including glutes & hamstrings and other stabilizers. This probably contributes to the observed higher natural cadence and lower metabolic efficiency on the trainer.

My theory is a fixed trainer changes core stabilization, with implications on pelvis stability and glute & quad recruitment (Lower hip joint specific power from muscles attached to an unstable pelvis, vs knee joint specific power from quads primarily attached to the femur). Aaaand possibly further implications on diaphragm & accessory respiratory muscles, breathing pattern, and upper body tension. But that’s getting really speculative.

References in the article.

Would be interesting to think about implications on differences in adaptations from riding the trainer vs road, as OP’s title implies. Are we going to see trends toward different physiology in primarily Zwift racers vs primarily Road racers? :thinking:


Yeah, that matches my personal experience. Riding outdoors engages more mucles, especially core stabilisation and arms! After a long spell of riding mostly indoors, my outdoor rides are really tiring. My legs feel ok, but the rest of me gets achy. Its better than not riding at all of course, but I’m amazed by stories of people building really good fitness by only riding indoors. (The type and place of riding might be relevant though. TT on smooth roads, yeah can see how that translates. Punchy rides on rough roads and surfaces, not so much).

Most of my fitness gains have been through indoor training. My power numbers indoors vs outdoors for extended durations (~20 minutes) tend to be pretty similar or slightly higher indoors (mainly due to terrain limitations). It doesn’t account for rough roads admittedly (although if nothing else rollers will teach you to ride smoothly in a straight line).

Rollers are probably different, because you need to balance. I meant if you only train on a static trainer indoors, you might be neglecting some muscle groups you actually need for riding outdoors (or on rollers).

Here is my hypothesis (which I kind of hope is true given the fact that I enjoy training both inside and outside) and also rings true intuitively for me;

The reason my ‘FTP’ is different indoors and outdoors is

  1. because I’m using the ramp test vs 20 minute test

  2. because I use more core / stabilising / ancillary muscles when ‘throwing my bike about’ outside versus working in a more linear plane on a trainer, and recruiting fewer muscles, but which are more cycling specific.

Following on from point 1, both tests have their place and as long as I adjust my FTP up 5% outdoors, my workouts (whilst RPE is lower outdoors) both have me at my limit ie I can’t push much beyond the power stated in the intervals whether indoor or outdoor. RPE is lower outdoors due to cooling affect and the presence of more distracting stimuli.

Following on from point 2, I suspect that a lot of people have this ‘FTP gain’ when cycling outdoors due to recruiting additional muscles, which gives a few extra percent to the power their body is capable of producing.

  1. People who do not have an FTP boost outdoors, are more efficient cyclists, who use more cycling specific muscles (born of the indoor trainer perhaps) and use less of the ancillary muscles, which, whilst giving a boost in the short term, are actually more energy inefficient in the long term.

  2. Training indoors boosts the cycling specific muscle system and therefore will lead to improved physiological gains over cycling outdoors, where we are also training these ancillary muscles, which can not be improved much, as they represent the 5% vs the 95%.

This is something I’d love to believe on wet and/or cold winter days, but how do you know it is true?

If I remember correctly from the part of Jem Arnold’s blog post on indoor vs. outdoor physiological responses, especially the glutes work much harder outside - and I don’t see what’s “energy inefficient” about this. Also in terms of training adaptations, as he points out in his blog, it might actually be important to train those auxiliary muscles (core etc.) because once you hit the road those muscles will have to work…

I personally will continue to try and do as much as possible of my training outdoors, as long as the weather is not so bad that it affects the quality of my session… (until I find some convincing info that indoor is just as good).

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I certainly don’t know that it is true - it’s just a hypothesis. But I rarely feel that the auxiliary muscles are a limiting factor for me when outside; it’s usually my quads / lungs that give up when I am on the absolute limit, and these are the things that indoor training does work on.

I personally feel that indoor training is harder (even when ratcheted up 5% outdoors) and that I notice gains from consistent indoor training that I do not see when training the equivalent amount outdoors. And I put this down to the fact that outdoors I can rely on these ancillary muscles - glutes, core, arms etc, which are not actually the determining factors when I’m racing.