wow thanks so much for the responses

, you guys are so kind!
I have to agree, if your overall feeling and state is better, including your physical fitness, it will probably also have a better affect on your playing. Even if you are a (professional) musician you should not sacrifice your body and health

.
I am asking because I have heard from a few people that lifting weights can actually have a bad effect on your playing such as, loss of speed and sensitivity.
For myself, I have been doing sports since the age of 4, and lifting weights since about 16 years old (now 22). Next to music, sports & exercising were always a great part of my life that I do not want to miss out on, even if I now have music as my "job".
From my experience, the only time that lifting weights interferes with your fingers and feeling, is when you try to play right after you have worked out. Your arms and fingers may still be "pumped up" and a bit shaky, so it probably isnt a good idea to work out right before a gig etc.
Right now I do lots of cardio and weight lifiting (for me its the best way to free you mind and the best balance when you do music full time). When lifting weights my goal is not to gain too much mass, but rather to gain strength and definition (less weight more repetion, just like "Risin Ashes" stated).
Anyway, thanks again for all your guys' input, its just great! I recomenned to anyone to do sports and keep your body in shape. So if you have anything to share on that topic feel free. Any further ideas, thoughts or maybe routines of exercising, just post here!