Power discrepancy

So, I have completed a search for an answer to this one but can’t find any conclusive reason. Let’s see if any of you experts can identify the actual issue I’m having.

Typical power figures across months of training. I am using the same bike, power meter and cadence is the same indoors and outdoors, it feels way harder trying to sustain the same power outdoors than it does indoors and it has me beat. Would love to work this riddle out once and for all.

Indoors 10mins (350W @ 150 bpm) 20mins (320W @ 145bpm)

Outdoors 10mins (331W @ 150bpm) 20mins (311W @ 146bpm)

Those numbers don’t look different enough to worry about.

Most peeps are the other way about. There is a physiological reason for this, I’m sure of it but not educated enough to know what the reason is - lol.

HR is affected by more than just the power you are putting out, so it’s not the best way to baseline efforts between indoor and outdoor. Below are just a couple of things that could be elevating your HR outside.

  • Cognitive load to navigate, pay attention to cars, etc
  • Upper body effort stay upright, steer, etc
  • Time of day difference between when you normally ride inside vs your outdoor rides
  • Fueling and nutrition differences, especially if rides are at different times of day (ie did you drink a cup or two of coffee before your outdoor ride that you don’t do before riding inside)
  • Thrill and excitement of just being outside
  • Heat, humidity, etc that affect cooling

There are probably many more factors to consider. I wouldn’t worry about it too much, but recognizing the differences is important. Like all training, it will require practice outside.


Thank you - guess you are right, more outside training!

What exactly are you worried about? I reckon your point is that at the same heart rate your outdoor power is lower. Overall, the differences are rather small, 5.7 % and 2.9 % to be precise, and I think show no appreciable discrepancy.

@rkoswald gave a good list of factors. Let me add another, and that is your power meter. The accuracy of your power meter is typically 1.5–2 %. If you have a single-sided power meter, then simply your leg balance might be slightly different. Let’s say your leg balance is 50:50 indoors and 49:51 outdoors. Your power will read 2 x 49 % = 98 %, i. e. an error of 2 %. If you are talking about a discrepancy of <6 % any combination will easily account for those.

So nothing to worry about, I think.


What kind of gearing are you using indoors?

Outdoors, are these numbers done on flat terrain or climbs?

Most of people get higher average watts on climbs. Indoor training with small gearing simulates climbs, while big gearing with a big flywheel simulates flats.

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Outdoors - on the flats, indoors using a Saris trainer and using gears to hit the right power. I do think the issue lies with it being relatively easy to maintain a certain power indoors whereas when I am outdoors, there are fluctuations, etc.

Thanks everyone for your generous feedback, I won’t give up yet.

Are those normalized power for the two rides? Or average power? If NP then ignore my post :wink:

Though NP is not the be all end all of performance, a 300W x 10’ consistent ride (indoors) versus 600W alternating with 0W in 1’ intervals for a total of 10’ (outdoors) will have the same average power but think of how different the perceived exertion is. Obviously that’s an extreme example but you get where I’m going with this. Unless your outdoor rides were in a velodrome with zero wind, I suspect your NP will be higher than average power. In fact, I wouldn’t be surprised if your outdoor NP is higher than indoor NP for the rides you posted.

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Thanks Andho, NP for both rides.