Undertraining indoors?

Looks like everyone here (at least TR podcast crew) agrees about altitude training to train low and sleep high because you cannot hit the numbers at altitude but on the other hand they don’t implement this logic for training indoors…

For example my FTP is at least 10% lower inside and vo2 max power is even more… so vo2 numbers inside are almost my FTP outside… and by “train low - sleep high” logic I should avoid indoor training if I can?

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Step 1 might be to consider why you have this difference, and alter your indoor setup to more closely match your outside numbers. I say this because many people are able to get their in/out numbers much closer or even the same. I can go into the possible influences and corrections if that is useful, but will reserve that for later.


Same bike, same powermeter, 2 fans and suito

Good info, also wondering about training mode and related gearing?

Then I still have to ask why you think this difference exists for you?

  • What might the limiter(s) actually be if we assume most other details are roughly “the same”?

Air conditioner?

Air flowing over you outside makes up for a lot. When I ride inside I need to blast the AC. Outside, I can ride 15 degrees warmer with similar RPE.

If I need to pick somethig it would be ERG because I don’t like the feeling, especially on ramp test but I usually don’t have problems with high torque riding (headwind), and then fans/ac because I don’t like the feeling of the fans blowing in my head (but I have them on max sometimes and still I’m not even close to my outside numbers)… and also I’m not the most stylish rider and I have a bit of movement on/with the bike…

But as far as I know I’m not the only one with (much) lower FTP inside…

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FWIW I was able to close the indoor vs outdoor gap by paying attention to ride feel. For myself on a road bike, that meant using the big chainring (higher momentum) and middle of cassette. Despite that, I can produce more power outside. For that and other reasons, I do almost all my training outside.

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I think “much” might be overstated. 10% is a lot and I think there is something going on there that you just still haven’t sorted out yet.

I don’t think the comparison is apples to apples with altitude because there are a number of other advantages to training inside that may outweigh the issue you are raising. Efficiency of time, safety, weather conditions, avoidance of terrain, wind speed, intersections and other road conditions that might affect an interval, sunlight, etc. I would certainly prefer to ride outside, but I don’t think I could come close to replicating my workouts outdoors.


There’s a huge psychological component to this that’s often not discussed, pinning it outside is just easier for most humans because you can sense speed, and speed helps motivate (and cool). I’ve spent enough time trying to bridge the gap of threshold and VO2 max training indoors v. out and I’m done. For anything above SS, I’m going outside.


It also depends on how much of your power is produced by moving the bike slightly underneath you. Being able to use back, lats, shoulders to generate power is much more difficult indoors when the bike is fixed underneath you.

Also, look at your cadence. I know I tend to spin a much higher (10 rpm) cadence indoors than outdoors, which leads to a higher heart rate, higher respiratory rate, and generally increased RPE (in ERG mode). Outdoors I naturally spin slower, which leads to it feeling easier (for me).

The whole “you’re just not cooling enough” is a red herring for a lot of people IMHO.


I could possibly add that a rocker plate might be a good option for someone to try in this case.

That is absolutely another primary reason for me. During the summer months I’ll do the hardest workouts in the morning while its cool, and due to heat acclimatization from hot afternoon workouts I see an additional boost in power in the morning.


That’s because the context of their assertion is completely different. At altitude, the limits of oxygen availability dictate that you cannot hit the same power, therefore you shouldn’t try to hit the same power.

There is nothing about the environment of the one’s indoor training room that would preclude one from being able to hit their outdoor power (unless you were training in an altitude chamber).

So, your statement “they don’t implement this logic for training indoors” is itself in error because you have misidentified the logic of their statements to begin with.

It’s all mental. Get a good fan or fans, and learn how to get the watts out indoors. Your body can do it. You just need to get the head right.


I have a similar issue. Exactly as you stated, 10% lower ftp and vo2max power even lower indoors. My 3hr power outdoors, I can bearly do that for 20min indoors. I’ve tried everything under the sun. I’ve narrowed it down to the fact that I’m getting contributions to power from my upper body that I’m not getting indoors. I’ve discussed this here in other threads, but I’m excited you asked the question as it always nice to revisit this and here other’s experiences.

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I’ve always felt this also was part of the difference for me. Like I get distracted on hard efforts outside so I don’t notice as much how bad I feel.

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  • Have you experimented with any trainer motion via thick foam, rocker plate or other methods?
  • If I read between the lines right, you are saying that the locked nature of a bike on a trainer prevents the motion you use outside, and therefore limits your power?
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I’ll try not to hijack the thread :wink:. Yes, the locked nature of the bike inhibits my ability to produce power the same way I would outside. Like trying to run with your hands tied behind your back. My HR indoors supports this theory as well.

I have tried the inside ride setup for the kickr. Although it introduced movement, it wasn’t free movement and actually made my power worse.


I’m not sure if the OP said he’s using erg mode or not. I could see that possibly causing a big difference in Power inside versus outside. I don’t have erg mode myself (so this is just a guess) but to me it almost seems like it would be easier mentally to not have to think about what gear you’re in while indoors.
I personally never used erg mode and have never had an inside vs outside discrepancy, only when using different power meters.

He mentioned ERG above:

He did not mention specific gearing in use or the trainer, which are all important to consider IMO.

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This is simply not true, and it perpetuates a “if you have trouble with it then you are just weak” perspective.

While this makes sense to let the bike move underneath you while stationary (so to speak), it doesn’t mimic the power contributions of outdoor upper body. When outdoors, the tire contact patch moves laterally relative to a rider’s center of gravity, allowing a very small amount of “pivot” that can be a point of power transfer. I think of it as similar to sprinters moving the bike laterally to gain torque but on a smaller scale. Indoors with the methods you mentioned, the movement at the contact patch relative to the rider serves to just absorb the motion, leading to instability. I’ve spent many hours indoors and outdoors wondering about this, and I think the TR podcast statements about “just get a fan” are more personal than they are generalizable.

I’m sure there are some contraptions out there that more closely mimic the dynamics than others, but the vast majority of users are on “regular” indoor trainers

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