This month’s NSCA Performance Training Journal (one of the benefits of membership) just appeared in my inbox. There is a great article on Core Training for tennis with Mark Kovacs as the first author (ran into Mark and chatted with him in the elevator at the ITF Conference in Valencia, Spain last November where I was presenting on mental training at each stage of an LTAD).
The article presents a solid rationale for current functional training thinking versus traditional bodybuilding methods. Obviously the part of the article relating to the serve and overhead training is less important for squash players, so I would recommend reducing the volume and sets of exercises relating to overhead training.
You can access the journal on their website or I have put a copy here for you (copyright and Fair Use restrictions apply): Core for Tennis and Squash?