Hi,
As one with ageing elbow joints I've always had trouble shaking aerosol spray cans for the whole suggested 2 minutes.
But have had a small brainwave, I have a reciprocating sabre saw and by taping the aerosol securely to a long blade have found the Ideal tool to do the job effortlessly for as long as I like. Paint mixed as never before !
There probably should be a health and safety warning here somewhere but you might like to try It.

Regards
Chris