Lifting weights will ruin your hands. They need all the rest they can get from playing bass. Carpal Tunnel??? I was a triathlete for 10 years. I lived to exercise, now I have aches n pains everywhere, at 38 years old. I was so naive.
But swimming is by far the best exercise for a prolonged healthy life. No impact, no weight bearing, good for the back, and you dont ever sweat.
