Assuming an indoor vs outdoor power difference: what are the consequences for interval training?

Training
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I’ve made the mistake of asking this question on Reddit and most of the people were just arguing about the problem not existing than actually be interested in a conversation about it. So my hope is that this forum will provide a discussion/conversation that’s a bit more on the actual topic.

Here’s my issue:

I can create a bigger amount of power outdoors vs. indoors (around 10%). I used different power meters to measure, I have a fully controlled training environment (AC and Fans), so heat is not an issue either. It’s not really new that a lot of people have a different power output indoors vs. outdoors, often times people talk about their indoor vs. their outdoor FTP. I really would like this conversation to focus on the question asked and not drift away into a debate on whether or not different power outputs indoor/outdoor are real :sweat_smile:

A hypothetical example would be a 10min interval. Let’s say I can produce 300w indoors for 10min and at the end of the Interval I’m completely exhausted. For the same amount of time (10 min) I can produce 330w outdoors and at the end of the effort I’m equally exhausted. The effort feels the same to me.

Here’s my question: are the intervals outdoors more effective as a training stimulus? Does the fact that I can produce a higher power in the outdoor interval (even though I have the same perceived exhaustion) mean that my training stimulus is higher? Because if that’s the case then I should as a result shift all of my interval sessions outdoors to maximize the stimulus and training efficiency.

Personally I much prefer to do my intervals indoors. I can focus on the power, don’t have to pay attention to potholes and the road surface in general and also don’t have to ride to an area first that suits the intervals I want to complete that day. But if the logic above applies I’d be wasting an enormous amount of gains by not doing my intervals in an outdoor environment.

Let’s assume for the discussion that motivation is not a problem. That I will consistently train regardless of it being outdoors or indoors. I’m really just interested in whether or not there’s any research/data/podcasts that deal with the question of the training impulse generated. As cyclists we oftentimes talk about marginal gains and a lot of people are willing to spend a lot of money to save 2-3 watts. In this context I think it’s a fair question and if it turns out that all that matters is the number you produce and not the perceived effort you put into the interval, then this would be a significant gain to leave on the table.

Really hope there’s a few more people that already put thought into this or can point me towards some articles/interviews/research/podcasts.

Thanks in advance, hoping for a productive conversation!

PS: if people take offense at the 10% stated, just make the assumption it’s only 5%. Even with a 5% difference that would (in my opinion) make a big impact on training IF the stimulus is really different.

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Hmmm removing all things physical…good sleep, nutrition, rest/recovery, etc.

Considering perhaps a 2% power variation between the two ‘power meters’ resulting in a 3% variation using your 5% instead of 10%.

So a 3% difference between indoor and outdoor power numbers might be considered ‘normal’. I’d consider/wonder about ‘rolling resistance’ of the bike/trainer…you don’t name the trainer you are using…compared to the ‘rolling resistance’ of the bike on the road as well as the wind direction, grade of the road during the interval, etc. Even a slight ‘false flat’ is going to change the numbers.

Perhaps there is also a ‘placebo effect’ when on the road…you are on the road and the feeling is wonderful compared to a trainer.

I’d guess the impact isn’t big but the numbers are going to indicate more and better increases in fitness especially if the RPE is roughly the same.

Numbers are just ‘indicators’ of improvement or decline and not an overall indicator of fitness or performance ability…as you know there is so much more that impacts a ‘good’ or ‘not so good’ training ride…just waking up and feeling ‘great’ prior to a ride is going to result in a better ‘training effect’ than waking up and feeling ‘blah’ or not good and pushing your way through the training of the day because that is what your ‘plan’ calls for and “I’m following the plan no matter what” perspective can really cause frustration when the ‘numbers’ don’t meet expectations.

Were it me and my power numbers are higher for a similar training ride when comparing indoor vs outdoor rides, I’d be happy and be sure to note the numbers, RPE, experience, etc. in my training log.

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I’d perhaps also consider the outside power numbers to be a more accurate reflection of the ride because the road rides are the more ‘natural’…taking into account all the things, other than the ride itself, that have an affect on the ride of the day.

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I really don’t understand why people start debating where the difference comes from, if it’s real and how big it is. That’s not the question :sweat_smile:

It’s pretty well established that a lot of people experience a significant difference in indoor vs. outdoor power. (hence the whole indoor vs outdoor FTP thing) The reason for that difference is right now completely irrelevant. The simple fact is it’s real. So based on that I think it’s a fairly good question to ask where the intervals are more effective, or if there is no difference since RPE is the same (aka. completing a specific time-window with the max power possible for that duration).

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How are you measuring the difference?

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IMO, a lot of people over think this. When it comes to key workouts, executing the workouts effectively is what matters most, despite a difference in wattage between indoors and outdoors. If you know what the delta is between your indoor and outdoor wattage then use that info. I don’t believe your body and how it adapts will differ because the stress is the same. If what I said is true, then executing the intervals with the prescribed rest should result in the same outcome.

This is just my take on it.

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I’m interestted in the discussion you are asking for. I have a pronounced power difference indoors and out - same power meter. I’m guessing it is something to do with the Turbo inertia/dynamics compared to road. My coach gave me an indoor and an outdoor FTP to use.

I am also interested in whether the outdoor workout has more/less or the same effectiveness compared to the indoor (lower power) version.

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I would recommend when doing a workout outdoors, start with the indoor power targets the explore what the outdoor target would feel like mid interval.

Let’s say your AI FTP is 300W indoors and you’re doing a 20min SS workout at 90%. I would first start the interval at 270W, if it’s feeling good 5-10mins in i would then explore what 280 feels like. I would then fine tune based off of that.

Continue to iterate until you figure out what works. Everyone’s different in what works for them. Best of luck!

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Most of the time the differences come down to actual inadequate cooling, or the inability to move the bike under you, while using core etc. to use power.

EG my indoor and outdoor FTPs are the same, but I have 2 lasko turbine fans at full blast for cooling.
That said, higher level efforts like my one minute power, I have like a 10% disparity cause when I get out of the saddle and do a 1 minute effort, it’s more natural for me to move the bike under me, use core and arms to torque the bars, rather than “moving around” a more locked in stationary bike.

Inertial differences could be at play, it’s one of the reasons some people produce better power on the flats or on the hills outdoors. If you find that you can produce your same outdoor power on the flats but you get stuck a bit more uphill similar to being on the trainer, then the inertial load thing may be at play.

I used to be like this in my TT hay day as I produced a lot of my power more at the end of my pedal stroke, rather than more evenly all the way through.

Now on the actual question at hand, what gets you better stimulus?

If the difference actually exists ( and it’s not a matter of power meter’s reading differently ) than the higher power will be “more stimulus”.

It’s the same reason that people in altitude camps will sometimes go DOWN to do their training, so that they can produce better power, get more training stimulus, and then go back to altitude for recovery and red blood cell increases.

This will be especially true doing vo2 and threshold type work, lower end aerobic work, it’s pretty well going to be a wash, ( i don’t think the difference between say 160 and 176 watts is going to be a major training difference, where the difference between 300 and 330 for threshold or sweet spot work would be )

At the end of the day though, just make sure that you’re not overdoing it if you use the separate numbers, it’s generally better to be slightly under cooked than over cooked, especially going into races, and you still get most of the benefits of each training zone even if you’re in the lower ranges of it.

But in terms of pure stimulus, then yes, working a 10% higher power will provide more stimulus, it’s up to you to balance it with your training needs.

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but perhaps understanding where/how the differences are is a useful tool when going from indoor to outdoor training rides and not being freaked out by big swings in ftp for the basically the same training ride…

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but perhaps confusion occurs when doing the same workout and seeing a 20-30watt difference…then wonder if the lesser wattage workout is producing the same training affect…

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Trying to answer your actual question, I am pretty consistent indoor to outdoor but a training partner does have a standard variance. He unscientifically claims that when his indoor watts go up by 10, his outdoor watts go up by 10 as well. Do you experience this?

That said, I thought I remember Kolie Moore having something to say on this issue. I thought his take was that watts are watts, and more is better, so train outside if you have to. Maybe a good question to submit to his weekend ask me anythings….or go search his old podcasts.

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Haven’t seen you answer this yet. Is this the same bike and the same power meter? Or, is there a potential it’s just a measurement error? This one matters - make sure this isn’t the case first. (Now that I look back - it looks like different Power Meters. Make sure you have tested them against each other, dual recording, and overlaid the power for the same workout. I’ve had the difference be as high as a 20+ w difference at threshold between two PM’s, for just the ones I’ve tested)

Short answer - dealing with two separate FTP, one indoor and one outdoor, is a giant pain in the neck and there’s no way to really effectively deal with it in the TR Ecosystem especially. You’ll have some workouts the system thinks you’re performing great, and others where you’re failing workouts at the same power.

You have a heck of a lot of assumptions and hypotheticals - try and get rid of those first. Same Power Meter, test the difference.

Here’s my not-so-hot take - If you have cooling and airflow sorted, and it’s not a measurement issue, A lot of times it’s really just the RPE and the person being a wuss and needing to HTFU. Zwift pacer group, music, try and get into it and stop focusing on what you think is your lower power indoors. I run into it too, there are days where it just feels harder on the trainer. But - it’s legitimately RPE and not a different FTP for me.

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I agree with the OP that outdoor watts are just a little higher. That is my experience as well and thought most people understood that. As to your question about the consequences of training one way or the other, I don’t think it matters. You should do whichever you like better and can be more consistent with. I’ve heard many a coach discuss intervals and how certain athletes will always ride the top of the range given while others ride the middle and how there is no difference physiologically because you’re close enough and hitting the same energy system. If anything, constantly aiming for the top just makes you more fatigued. What you really want is consistency. It isn’t what you do that one week, it is what you do for the last 40 weeks that matters. So if the indoor trainer and erg mode and a fan and music helps one be consistent and knock out the intervals perfectly over time, that is going to be better. If someone absolutely hates the trainer and loves to ride to a certain spot near them where they can get their work done, then that will be better for them. But I don’t thiink you’ll end up being way stronger one way or the other just because you can do a little more power outside.

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The stimulus is the stimulus. The reason we train indoors is the consistency ie no traffic lights, uphills, downhills etc for the time we spend on the trainer at consistent power is the stimulus we are looking for and now with AI picking the the right workout for our current level. The stimulus is more about accuracy of level than what you think you can do ie less is more

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Seems like there are 2 possible scenarios:

  1. Indoor and outdoor training are nearly identical which would imply it is just measurement error. You are doing the same workout producing the same training stimulus.

  2. Indoor and outdoor training are not identical which would imply there is some factor(s) affecting your performance. You are doing different workouts with different training stimulus.

Assuming there are factors leading to real performance differences (2), the question is what are those factors and how do they affect your performance.

In the extreme, you could purposely train in a hot room and maybe that helps with performance in heat.

Less extreme, maybe there is just more natural variation in effort/power outside so even if average effort is the same it feels less taxing than a less variable, unrelenting effort inside.

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You’d be amazed how many people think their indoor fan/cooling setup is dialed, even while also complaining about the pools of sweat under their trainers and lower indoor power lol.

I’ve had that exact conversation, and in one breath they are soaked, have to change clothes, and power sucks, but in the next they claim their cooling and airflow is more than adequate, even getting offended that I suggest otherwise :stuck_out_tongue:

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I think someone has already said it, we train for the stimulus for the body to improve. Doesn’t matter which FTP is higher, that your FTP for that environment. If your Indoor FTP go up, your outdoor FTP should go up as well. I believe the amount might be a bit different because I believe outdoor riding has a lot of micro coasting that we don’t notice hence FTP is higher outside.

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maybe there is just more natural variation in effort/power outside so even if average effort is the same it feels less taxing than a less variable, unrelenting effort inside

I think this is a very relevant point.

Using @TKilian ‘s original example of 300W indoors for 10min vs. 330W outdoors for 10min: you are comparing the mean wattage across the 10 minutes. In order to evaluate the training stimulus, you also need to take into account the variance. If, as suggested, there is greater variance outdoors than indoors, then your question becomes: How does the training stimulus compare for 300W for 10min with variance x versus 330W for 10min with variance x + δ? I have no idea what the answer is, but if the variance does differ in this way, then it is no longer so obvious that the higher mean wattage would lead to a greater training stimulus.

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If there is a greater variance, the NP would be higher - so presumably a bigger stimulus?