Apparently Wenger wants them to be in line with matchday surfaces.. ( much harder than the more representative, softer pitches used by clubs for training purposes ).
I don't know if this is bollox but the stats seem to support the accusation that we suffer far more injuries than any other side.
http://www.justarsenal.com/ian-wright-agrees-on-why-arsenal- get-so-many-injuries/45824/comment-page-1