I am starting to question this as I see so many guys in the parks where I train cycle by and also looking at the professional cyclist's bike set up. It seems all of their bike stems are parallel to the ground, whereas when I went for my bike fit to get professionally fitted, they had to put a new stem in and have it pointing up and my handlebars are 2cm or mm, forgot which, below my seat, whereas these guys all have their stems quite low.

The fitter told me to get that stereotypical picture of how a road cyclist should look out of my head. But why do they all seem to have quite a similar set up? Aerodynamics or something? Seems like they are comfortable too but when I try it it is pretty uncomfortable

Aerodynamics

A bike's fit should have nothing to do with looks and everything to do with how it feels for the rider. But yes, aerodynamics is the reason for a slammed stem and low handlebars.

Placing the bars only 2cm below the saddle would be a recreational fit, intended for comfort. Racers nearly always use a much larger saddle to bar drop to improve aerodynamics. One of the keys to using a large 9-11cm (around 4 inch) saddle to bar drop is having the saddle back far enough to balance your weight over the saddle, so there is little weight on your hands. Fitters who use the old knee-over-pedal method of positioning the saddle, will often have it too far forward for comfort, using a large saddle to bar drop.

Changes to the saddle to bar drop should be made slowly, so you have time to get used to the change.

Several years ago, I made a change from a 9cm drop to 11cm all at once and it worked out fine, but that's probably because I had been using such a large drop for many years prior to the change.

The more flexible you are and the greater core strength you have, the more saddle to bar drop you can comfortably ride, and the more aerodynamic you will be. There are other benefits as well such as recruiting stronger muscle groups. Don't get sucked into the 'slam that stem' mentality though that's rampant among cyclists. Ride what's comfortable. An aggressive looking bike is worthless if you don't ride it because it's uncomfortable. I found that the more I ride, the lower my bars can be in relation to my saddle.

If your fitter took bodily measurements, stretch capacity - probably fit the bike in a sane way for a non-pro. The alternate is getting that slammed look which can be very uncomfortable, and given some body dimensions like the gut/lunch muscle girth, reach not very practical if someone isn't able to breathe and gets cramped after being hunched over like Quasimodo.

Yeah, out of the three choices for fitting, aerodynamics, comfort, and efficiency, I chose comfort to be one because I had do much pressure on my hands and my lower back also started to hurt. So I am riding a recreational fit now. though on the drops, I can get my back completely parallel to the street if I need to which is handy.

I still can put out decent power though with my fit, and that's also what the fitter does too because he isn't flexible.

Yeah got measurements and all of that. Comfort was my #1 because of my sore wrists/hands and lower back, #2 was efficiency, whatever that does to the fit, and #3 was aerodynamics

There's a coach/bike fitter, John Cobb that has some interesting ideas about bike fit. https://www.cobbcycling.com/content/ComfortandPower

There's a few youtube vids he has too.

It becomes pretty obvious to anybody that has ridden into a strong head wind that the less frontal area you offer the easier it is to move forward.

yeah thats when I go into the drops!

My seat can't do much higher though because then I don't have that 10 degree bend at the legs: i'd be scraping and pulling on my achilles tendon

With my fitter it was #2 , #3 . I put comfort last as I have a hybrid, MTB which I can tool around in - albeit slowly. That said after a few hours on the carbon bike I feel it a little bit in my lower back. But not much which is pretty cool given that I am not all that flexible. Mixing it up between bikes is pretty good overall, though I must say I like being able to blow away other roadies if I am with it that day, whereas I can't do that at all with the hybrid, MTB, and barely with the belt driven bike I recently got.

I think aesthetics have more to do with it than most people admit. I could still get my bars pretty darn low using a slammed stem with some rise, but it looks like dick, imho. Zero effective rise, parallel to the ground, just looks right, comparatively a 5-15 degree rise looks like my bike is happy to see me. When I replaced the stem on my cross bike I got Thomson with a 5 d rise (I'm thinking) and flipped it over, the result is a nice parallel stance to the ground..perfect. I'd rather add some spacers than go with a "happy" stem.

I flipped and slammed my stem last year, succumbing to peer pressure from the 41. I'm very impressionable like that.

I rode it for quite a long time and a few thousand miles like that and enjoyed it very much, but, unfortunately, this year my lower back has been acting up and I was having spasms after riding so I re-Fredified my bike and unflipped and unslammed it. And it's much better...doesn't look as cool but I don't need to rest a day after long rides.

Sore wrists and hands is a sure sign that your saddle was too far forward. The proper fix for that is moving the saddle back, not using a very small saddle to bar drop.

The bend in your leg at the bottom of the stroke should be closer to 30 degrees, not 10. The angle of your foot affects the angle greatly. Most cyclists pedal with the heels up by some amount. If you clip into the pedal and set the saddle height so your foot is level and the leg fully extended at the bottom of the stroke, all it takes is a 2-3cm rise of the heel, while pedaling, to create that bend at the knee. Of course, if you pedal with no heel rise, then you'd lower the saddle from that starting point, to create the knee bend.

CAPTION: "Why don't you go out and ride with the boys more? Stop moping around here on a perfectly fine day. Who cares if your stem isn't slammed like the rest of them. It's comfortable for you, isn't it?"

Bar to saddle drop is more dictated by a rider's flexibility than anything else.

Yes, a huge drop will be more aerodynamic. But when a rider exceeds his or her flexibility level, he or she loses power. Any aero gains will be offset by power losses.

OP, work on increasing the flexibility of your hamstrings, hip flexors, quads and glutes, and you will soon be able to lower your bars.

yeah he did move the seat back and that alleviated the pain almost instantly. i was riding before on just how i got the bike from the shop for about a year, but it wasnt until i started doing big miles where I felt the pain