Riding more to 'train up' may not be appropriate.
Not a doctor, always ready to 'stand corrected' when proven wrong. I should go back thru some of my medical history and prior notes, but not at home.
When your muscles work they produce enzymes (and other stuff). If one of those (iso)enzymes is produced in excess it leads to persistent pain (a dull ache). People with MS have extremely high levels of this enzyme. I was found to have an elevated level. No matter my build-up and training, riding long and/or hard miles degrades my ability to ride strong. Have a blood panel taken that checks CK levels (I think that's what it's called); and YES = it feels much like lactic acid build-up. Finding a balance is the trick. No more centuries for me unless they are metric, KOM is beyond my reach.
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Vintage, modern, e-road. It is a big cycling universe.