I haven’t used EMS so I can’t really say, but my guess is EMS would increase force through increased calcium released and possible changes in pennation angle of the muscle fibers. This would be similar to PAP however PAP also “primes” the nervous system. Someone with experience using EMS could probably help you on this topic.
In regards to Hodgson’s review use pubmed and search “Hodgson PAP” it is the fourth article down the list. The first article is pretty good as well