guitar and piano

[A-Flat]

I play piano but recently i have started playing guitar. Playing guitar often involves strenuous finger contortions in the left hand, which sometimes have to be held for a while. This makes my hand ache for a while usually...Anyway I was wondering if anyone knows if playing guitar could have a negative impact on my ability to play piano with the left hand, by changing the hand muscles or whatever. Any advice would be much appreciated.  

[Wired]

I've played both for years. As with anything else, if you're feeling strain, it's time to call it quits for the day. If you end up going too long when it starts hurting, you may actually injure yourself.

Anyway, I play Bass, Guitar, and Piano, and I don't feel side effects from any of it. Well... except for when I don't play the bass for a while and get blisters on my fingers when I pick it up again