There are definitely some myths surrounding muscle-building and its dangers for the hands of a musician. Yes, it could potentially be dangerous but improper practicing and even typing on a computer keyboard have also caused severe injuries. It’s all about misuse and overuse when your talking about danger.
As a musician, you are, believe it or not, an athlete. Your body must be in reasonably good shape to be resilient to the physical and mental stresses of being a performer. Working with weights can improve posture and also relieve spinal curvature that may result from sitting in the same position on a daily basis. It can also release a lot of the nervous energy that may come from a hectic performance schedule, upcoming audition, etc.
Most people think that to have an athletic physique that you need to work with very heavy poundages. Not quite. Try to go for lower weight but very long reps in which you control the weight for it’s entire duration. Everyone makes a huge effort to bring the weight up but then they let gravity bring the weight back down. Instead, resist gravity in the negative portion of the rep. This will make more moderate weights seem heavier to your body and you will great an amazing workout.
Try this very basic exercise for your bicep training. As you do dumbbell or barbell curls bring the weight up in 1-2 seconds and bring it back down in 3-4 seconds. Never lock your arms, either at the top or bottom of the rep. Each rep will feel like the equivalent of 2 or 3 faster reps, maybe more. This is called training with negatives. Micro-trauma (muscle tearing that causes delayed onset muscle soreness-and later hypertrophy) occurs during this phase of the movement.