somehow made a dupe post: original here
https://www.bikeforums.net/showthread.php/731070-Fit-Placebo-Effect-or-Not

I made some adjustments to my setup the other night. Raised my saddle about 6mm, and repositioned my hoods so my wrists weren't at such a strange angle as I had taken a spacer out the other week and never changed the bar position. I felt as if my hips were rotated to a better position, back felt straighter, and less force on my palms, more balanced overall. As a result on my typical ride to work I arrived in 12m23s which is about 1min faster than I've ever done it before within the past few weeks.

So do I rack this up as a placebo effect or did the change in fit really contribute to the decreased time.

It's easier to be more efficient when you're not having to overcompensate for a poorly fitting bike. Changing your fit sounds like it helped.

Irrespective of whether or not I believe bike fit is a placebo, ask yourself this:

If you felt more comfortable and/or more powerful (faster) after changing your bike fit, why would it matter whether or not it was a placebo?

I find that I rode a older 10 speed that was not my fit:

My legs felt like springs
my back was wrecked
I was tired afterward
everything hurt

When I bought my current mountain bike that fit me:

My legs feel great after a 40 mile ride
no back problems
I also work out my arms
it feels "natural"

With this, my speed had probably increased by 3 to 4 times

either you were really slow before, or you're superman now. i wish i could increase my speed 3-4x...i'd be passing cars on the highway.

and OP, it's probably a combination of both, but i agree with bob ross. even if it didn't make you faster, it made you more comfortable, so it's worth it for that alone. if you got faster, too, even better.

I was just equating fit with equipment upgrades like wheels. Most of the time people will say I got a new set of wheels now I'll X times faster than before and 98% of the time it's just a mind trick that the new equipment made that much of a significant change in performance.

I think a lot of your minute was up to something else (wind, rest/food in prior 24 hours, etc). Part of it was probably due to being able to recruit new muscles (do you feel a bit sore?). Your description lead me to believe that your position is much better now.

I think fit is absolutely critical if out of acceptable range. For example on Mon I rode and noticed my left foot wasn't totally comfortable when at the bottom of the stroke - I felt it was reaching a touch. Wed I checked my post, noticed about a 2 mm difference in height (based on pic of the seatpost and the logo on it when I first built bike in CA, and position there was great). I lowered the saddle, went for a ride, and my foot was okay at the bottom of the pedal stroke. Minor change, minor difference in behavior, but I think this kind of thing can eventually become problematic if left alone.

If I'm another mm or two lower, I think it'd be okay, hence my statement on "acceptable range". If I get too low then it affects bar drop, my back angle, and therefore my back. It's more comfortable for me to have the bar drop I prefer so I try and keep it at that amount.

I don't think I'd go from doing a 13:30 TT to a 12:30 TT based on a few mm difference, but I could see dropping maybe 10-15 seconds initially. The rest of it may be due to the riding conditions (wind, humidity, etc) and your own prep (food, rest, mental outlook, etc).

Whatever, a minute off is a nice improvement. Congrats!

See if you're consistently faster going forward instead of basing it on a single ride.

N=1

So you made a post and linked it to itself? Hilarious.

Fit is important.

However, timing a commute doesn't really work. Your measuring instruments are imprecise; there are too many variables; you don't have enough data (one ride is hardly enough evidence to draw any sort of conclusion).

Thread incepted.

fixed, sorry

Fit is important. When my fit is right, I can climb like Hans Florine, have a cadence like a centrifuge, and descend like a falcon. These are all exaggerations, but they sound good, no?

Seriously though, I think that fit is one of the most important upgrades you can make. I agree with CDR, but would like to expound that usually fit doesn't make you faster, so much as it makes you more efficient (which is faster). As an example, if I'm taking a long solo into a fierce headwind and my fit is right, I can churn along for several miles in the IAB or drops position, and for the most part, all my muscles have to focus on is what it takes to keep my upper body still while my lower body works toward steady locomotion. If I were to have my saddle height changed by a few millimeters, and do the same run in the same conditions, I would be more fatigued in few hundred yards. The reason for this is simple, the fewer muscles that are working at stabilizing your body, keeping you aloft, and keeping your joints in alignment, the more of them can go into moving your legs. The more efficiently you propel yourself, the longer you can do it at a given speed/caloric intake.

I'll take more sample, N=10 should be a somewhat better data set

Think of your body on the bicycle as a machine. If every part of the machine is in its optimum position, the machine is going to operate better than if something is not set up quite right.

MAybe it's time to invest in a specialized BG fit.

If it's a placebo, it will vanish. If it isn't, it'll stick.

ftfy.