It isn't just the weight but how you handle it. I was careless the day I pulled a muscle in my back loading a heavy 88-note Kurzweil in it's flight case into a gig and I'm lucky the damage was temporary, but none the less it was the day I decided to switch to a lighter keyboard. Back injuries are career-threatening, expensive, and painful so no keyboard is worth the risk... yet "portable" keyboards in the 70lb range are not uncommon. It's hard to justify why a portable keyboard would weigh so much nowadays... home units are a different story. Personally I won't have anything for stage use over 50lbs and I'm kinda big and work out regularly.