Ouch -pain in quads

Well, I for one am glad we could all help you reach your own conclusions

Johnny, you are describing being fucked... its fine. 

if you keep going, day after day, you can really climb in the box. When you lose all use of anything remotely fast twitch muscle wise, thats when you know you are there. 

Johnny, you answered your own question... you had a bike fit.. .went out and rode the longest ride to date.

Your muscles were ripped up. Perfectly normal. 

When you had your fit, were you not told to take it easy for a few rides?

I remember when I had my first proper fit... told to take it easy. Raced 36hours later. Won the race (yeah), but man my legs were in bits from it. 

What I would say though is that the sore quads could be good, or could be bad... good in that your new position is engaging your quads more, so that you can use them to create power... bad in that you might be isolating your quads as the primary muscle to generate power, and so overloading them on longer rides. Keep an eye on it, if you are still getting sore quads ina  few weeks and/or you are not progressing fitness wise, then maybe consider putting your saddle a little fruther back in the rails. 

As for glycogen depletion causing muscle pain, I'm not sure I follow. if you run out of fuel, then I'd assume that the strength of muscle contractions  would diminish, making you less likely to damage muscles, not more. 

If you saying the riding you did to empty your glycogen stores did the damage, then I follow you. 

"I did 57 miles in 3 and 1/2 hours. "

How old are you and how long have you been riding, what do you normally do each week etc? These are all really important factors in the asnwer to the question!
 

I used to run 3 or 4 5km runs a weekbut for the last few months i've been utterly inundated with work so i've been pretty much sat down for since Christmas Friday afternoon I decided to go for a bit of run and clocked up just over 20k in under 2hours and now I feel like death it will go in a day or two.

Sounds just a bit like DOMS going from inactivity to doing more than you'd normally do will always cause it, like has been said before a bit of MTFU, a bit of Radox and a bit of gentle massage will get you through it. 

But rest assured each time you go through this bit of pain the next time you do the same the pain will be less

did the bike fit change your previous riding position?

good answers, but I think if it was just fatigue you'd be feeling it in many other places too - why so specific to this one area?

if you have a neutral position on the bike, then the leg stroke should include the calfs and glutes even more than the quad, so you'd feel it down the backs of your legs just as much.

I've not done much by the way of long distance rides either. What I find is that anything over 3 .5 hours starts to get.... different. Less fun and more like hard work basically. I think it's down to the glycogen stores in the muscles being depleted by bursts of anaerobic activity and at that pace it will happen. Fuelling doesn't help much because it takes time to replenish glycogen.

My advice would be this. Don't try to man-up, soften up. Pedal more softly than you would on shorter rides and go especially easy for the first  forty minutes while the legs get warm, that will reduce the rate of glycogen use. Pre-hydrate, and drink early in the ride. And carb load: do some hard sprinting to shock the muscles and eat like crazy the day before the ride. Good luck.

nick t may be right. There is always muscle pain after exercise. If its a dull ache probably accompanied by a warm feeling that sounds like pushing at your limits which is good it will make you stronger.

if the pain is more sharp or if you have asymmetric pain, then you may have pulled or strained something. If both legs feel the same I wold put it down to working the muscles harder than you have before. 57 miles in 3.5 hours sounds like a good pace. see how it feels in 2 days, and try to keep the muscles moving in the meantime.

I wouldn't be concerned with muscle pain after exercise, especially if it's your longest effort to date. That's what exercise does, it breaks the muscle down, no amount of fuel will affect that you just rebuild it stronger for next time. Fit issues tend to manifest in the other tissues, ligaments and cartilage etc so it's good to learn to spot the difference. 

I would check the saddle height, tilt, and fore/aft alignment