Why am I feeling it more in the backs of my legs when I push it on the flat?

I've noticed recently when I get down on the drops or elbows bent on the hoods and put out a big effort on the flat it's my hamstrings that start burning - barely feeling it in the quads. Conversely, on the turbo I can definitely feel it in the quads when I do a sweetspot / threshold interval.
Also I'm getting a bit of a niggle in the knee. Kind of hard to put my finger on exactly where in the knee but I sometimes feel it when I pull my leg back or if I bend over forward with a bent knee. Seems to affect both sides so I'm guessing (hoping) it is a fit issue.
Any ideas what I might need to tweak. Am intending on getting another bike fit soonish but finding the time/money is tricky at the moment...
Also I'm getting a bit of a niggle in the knee. Kind of hard to put my finger on exactly where in the knee but I sometimes feel it when I pull my leg back or if I bend over forward with a bent knee. Seems to affect both sides so I'm guessing (hoping) it is a fit issue.
Any ideas what I might need to tweak. Am intending on getting another bike fit soonish but finding the time/money is tricky at the moment...
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1) There should be NO difference between work on the turbo and on the road
2) Adjust things like saddle height/setback etc etc 1 at a time.. but really , really how many soddin things can you actually change?
3) You can work it out yourself and SAVE money , you aint a complete novice.
Try running your finger more slowly across the affected area
Also, I probably don't try for such an aggressive position on the turbo - generally on the hoods at the most.
I do still get a bit of the knee niggle from riding on the turbo though.
Be careful as hamstring injuries are a nightmare. So spend time to get the set up right.
When riding hard on the road it feels like a lot more power is going into the bottom part of the pedal stroke. I don't really get this feeling on the turbo - more just the pushing down.
I suppose the lesson is to make sure you replicate and train specific road positions on the trainer...
Tbh, given this info, I would say you are just straining more outside due to the resistance of the road surface, terrain and the wind.
It could be you are trying to put out more power due to this, which perhaps is putting strain on your lower back and causing the hamstring pain.
You could try increasing cadence to maintain speed to see if that makes a difference when in the drops.
I would strongly suggest you check your saddle height and position though.
When you go on the drops your upper body position changes and stretches out but your leg motion/ action barely alters.
Have a retul fit (or equivalent) and you will see from the video/ photos that your leg motion remains pretty much the same in or out of the drops.
However, being on the drops does put more strain through the lower back, which of course is connected to the hamstrings, so in this sense it can affect them. This is where you need your glutes working.
If you are feeling it in your quads indoor and hamstrings outdoor then you are likely using different pedal stroke actions, which indicates a position issue (likely saddle height) or perhaps lazy glutes, or both.
Think I'll put the bars up 5mm too and see how that feels.
It's getting to suck a bit when it feels like all the niggles are holding me back rather than (traditional) fitness...
I know it's frustrating but it's probably better to have a good bike fit from an experienced fitter.
If you do keep tweaking things yourself you may end up like this:
https://www.youtube.com/watch?v=8mdwAkWvWMw
I've put the saddle forward 5mm and raised the bars 5mm and it feels generally, a lot better.
I suspect the difference in feeling is more down to being in a more aggressive position on the road when putting out similar watts. I figure lower is going to stretch the hamstrings more and that's what I'm feeling.
Will probably get a bike fit soon though - try and iron out a few other niggles...