Haven't had a really heavy bass since my MIA Fender P Deluxe from around 2000/2001. Awful bass, looked great, sounded awful, weighed FAR too much. The normal P bass tone is much better.
BUT, and this is the big but, musicians aren't usually (although there are plenty who are!) the healthiest of people, especially those who work and then work as a musician. Late nights, unhealthy food, and lack of sleep can have a huge effect on your life.
This hectic lifestyle means that the gym/exercise is usually hard to fit in.
I'm only 31, and the best thing I did was listen to my girlfriend, and my fitness fanatical Father, who said 'exercise and you won't feel as tired at work'. Works 100%! I'm barely ever tired now. I work out three times a week, and sometimes I actually get into it! I put my exercise before any practice, as its as important as sleeping. Get the right balance and it helps.
Why does this help with bass weight? Well, part of my fitness is kettlebell workouts, which is all about building up muscle and toning them. There are many back, leg, arm and chest workouts which help to make you have a stronger core. The stronger the core, the less you will care about a heavy bass. Trust me, it works. I can pickup bass cabs, PA cabs, etc, with less moaning, and my goto Ray 4 H, which is perhaps my heaviest bass (not stupidly though...maybe 10-10.5) is fine on long gigs.
I agree, if you have a lighter bass, its easier anyway, but the exercise and care for your back helps with all parts of the gig, including load in/load out.
If you have an injury or condition, then its different, and you can only see what the tolerances are.
Hope this helps. I hate preaching fitness, but I used to be quite lazy, and now im the opposite!
