The verb looks like it is in position 3.
This is not how the V2 rule works. V2 is the last resort. The finite verb is neither at the beginning nor the end so it must be in second position (though there is, of course, an exception even to this rule). This means
Vor allem Trainierte
is one item. Because V2 says, all the stuff in front of the finite verb in second position is one item. (Apart from particles. Particles break any rule.)
In this case, it's the subject: trained persons in particular.
What is 'Trainierte' in this case?
It's a noun made from the Partizip II of the verb trainieren: trainiert. You can make different nouns from a verb
das Trainieren — practising (from Infinitiv)
der Trainierende — the practising one (from Partizip I)
der Trainierte — the one who has practiced (from Partizip II, perfect interpretation)
der Trainierte — the one who is coached (from Partizip II, passive interpretation)
This systematic is applicable to all German verbs and German speakers use it all the time. Some verbs allow one more form
die Platzierung — the result of platzieren ("-ung-Form")
This doesn't apply to trainieren though, for unknown reasons. Maybe because people differ what the result of trainieren is.