I am now 73 with a bad back. Moving heavy amps... not long ago I owned a 150 lb amp and moving it is simple. You use your brain. You break down what you must accomplish and then use leverage, gravity... and typically sliders and maybe a hand truck to accomplish it. I have never failed and not needed any strength or sprained my back.
Furniture sliders, some come with a little lifter ... like a really small teeter tauter that you step on to lift a heavy object so you dan slide it into position.
Unboxing simply requires thought and rolling.
Wood plank if you need to slide something into or out of a car.
It is simple. Just think.