Indoor vs outdoor power output: Are they different and why?

      There is a commonly reported complaint about indoor wind trainers; power output is lower than the road. While Zwift is an awesome indoor training platform, the aforementioned comment has been showing up a lot in my feed, along with suggestions on why power is different indoors. Recently Zwift posted a video by coach Hunter Allen, who provided his own explanation for this discrepancy. For the sake of brevity and transparency, I recommend watching the video yourself. While some of his insights were correct, his explanation overall just didn’t make sense. Most notably, Allen’s claim that power is 20-30 W lower indoors; that’s about 10% for most of us. That’s massive, and highly circumspect. Here’s my breakdown and counter-points to his explanation:

1) There’s no evidence that power is consistently 20-30 watts (10%) lower. That’s a huge impact in one direction, and one I’ve never seen; 5-10 W is more plausible. Moreover, I’ve got enough data to show that power could be higher, lower, or actually not much at a given effort.
2) Power is a work rate over the whole pedal stroke. In simplest terms, if it takes me 1 sec to complete a revolution and I generate 20 Nm in one direction or 5 Nm in 4 directions, my rate of work is the same.
3) The “feels different” mechanism is meaningless, and cannot account for a difference of 20-30 watts. If that were the case, we would see a feels different response more often, including most notably, in the lab on big ergometers. We do not.
4) Work output should be largely independent of psychological factors. I could imagine difference of 1-2% for a placebo/nocebo effect, but not 10%. If your head is losing you 10% you’ve got some serious issues!
5) Related to 1), power could be higher or lower due to a greater resistance which causes you to increase force (torque) at a given cadence (e.g., lower tire pressure, more pressure on tire-drum contact). In other words, you try to pedal at a common cadence but work a lot harder, and hence fatigue. The opposite could also be true.
6) If you train at a power 30 W lower then you are training at a lower load, period! This is a problem with training in super hot weather or altitude. If you train at altitude all the time you actually detrain.
7) You can and should train with and without a fan. The added heat load has beneficial adaptations.

What are your thoughts? Drop me a line or comment!

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2 Comments to “Indoor vs outdoor power output: Are they different and why?”

  1. Jsn says:

    I think Hunter Allen is full of hot wind. Just friend him on FB and look at the complete nonsense he posts that isn’t related to fitness and you’ll soon ask yourself why you believed anything he ever said. I threw the books he wrote in the trash a while ago.

    • Tradewind says:

      JSN, Hunter and I go back pretty far and its unlikely he’d accept a friend request. Its not productive for me openly discuss why, but I don’t need to wonder. This is no different from Carmichael’s nonsense in the late 90’s only to learn that he never even coached Lance. Ultimately Hunter found his niche and has simply been spinning out the rhetoric to fuel his business; he definitely knows how to run a business it seems. Putting aside those differences, though, its important to get down to the evidence of his claims, which is completely lacking. Rather than be open to an alternative hypothesis, he chose to “appeal to authority” and cite data he won’t reveal. Even if I published a study refuting everything he claimed, he’d probably stick to his story to the end. Fortunately for me, I never wasted my money reading those books, which simply steer you into buying his software. As a friend and very good coach who also knows him said to me, “Hunter’s a snake oil salesman.”

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