That's not muscular, that's the famous runners' Shin Splints. Search this forum for loads of advice on what to do (and sorry, a lot of the advice is from me )
My shins hurt until I bought some running shoes. I ran in quite grippy trainers without much give. Went to a running shop (with a paper bag over my head so no one could see) and bought some running shoes as advised by them. No more shin problems.
I know that I've posted this before, but it remains funny and with an element of truth:
Remember the 4 permissible reasons for cutting a run short:
1) Sudden, sharp pain in chest
2) Seizure, asthma attack, fainting, blackout
3) Greenstick fracture (bone comes through skin)
4) Uncontrollable bleeding.
For everything else, you're not allowed to stop running, but are allowed to slow down.
One thing to add - if you ever come across a runner suffering from any of those 4 things, remember the most important thing that you can do for them is pause their Garmin. Only then phone for help.
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