I've heard only "envaramiento", so people say in Spanish
Estoy envarado por haber nadado ayer.
Wikipedia says it's said agujetas, which I've never heard. Is there another non-medical term for muscle fever?
According to RAE agujetas is correct, and it is a term I have heard several times the day after playing an intense football match, skiing,..
Dolor muscular is self explanatory.
The medical term would be mialgia, and in English is myalgia, origin on the greek words myos(muscle)+algos(pain)
Envaramiento it is a new word for me but is correct:
Envaramiento es la acción de envarar o envararse
Entumecer/entumecido is repeated on these definitions so it is correct.
In my opinion all these alternatives should be used when is painfull and makes it hard to move.
An alternative could be punzada or tirón muscular, but it is usually used when the pain is strong and short:
An example: Desde que tuve el accidente tengo unas punzadas en la espalda que no me dejan dormir.
In fact several Catalan speakers use it in catalan (agulletes) but it is not correct, and this is due to the Spanish influence (agujetas).
There might be regional terms for that, but I've never heard anyone say "envaramiento" or "agujetas". A more regionally neutral way to say it would be
In Mexico we say "entumido" (numb) or "adolorido" (in pain). I'm not sure where in Mexico they say the former, but in Guadalajara we say the latter. For example,