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Had it on occasion before but it tends to ease quite quickly especially if the going gets easier. Had to cut short todays ride as the pain was excruciating and was not going away, they are burning/tingling as I type this :(. Anyone else get this ? it's most unpleasant like permacramp.
I kind of have experienced this - how much stretching are you doing and how often are you doing it?
I've now stopped, but once I got myself doing daily stretches this pain definitely reduced noticeable, so I put it down to my getting old and never stretching and assuming I can bend myself in all positions like I could as a youngster - absolutely no chance of that but I'm too stupid to get some stretching planned into my day-to-day routine to help.
How much water are you drinking? It might be aided by a bit of dehydration...
No medical awareness, so the above could be absolutely unhelpful.
Do you also have pain whilst walking or doing any other activity?
Sounds like shin splints.
Do you go running too?
Changed your cleats/shoes recently and maybe not got the cleats set in the right position?
Is it from the outside of the knee cap along ish where the calf joins the bone ? Or the back outside edge of the calf ?
same old shoes and cleats
walking tends to ease it
no running

I still have a dull pain there.
Looks like peroneus longus and brevis.
Might be worth moving your cleats back.
Will be worth massaging and stretching them.
I find something like putoline is good for massaging my cleats. Stretching them more of a challenge
I get that when i move the saddle 5mm too far forward. Try moving it 5mm backwards. Slightly lower might also work.
I find a couple of minutes of foam rolling really helps with my calves and shins before a ride/run. More issues from running than cycling though I expect it could be the latter exacerbating the former.
e.g. https://barbend.com/best-foam-roller-exercises-legs/#MSR
think it turned out to a bout of tendonitis, seems to easing up with time.