Square dancing 9 hours is definitely not appropriate, too long on the knee joint damage, now the square dance is more and more difficult, usually designed for a lot of body rotation, lower limb twisting action, these actions on the body center of gravity control, lower limb strength and stability have high requirements. Dance time of more than one or two hours at any one time means too long continuous use of joints.
Square dancing is not the longer the better, the difficulty is not the higher the better, appropriate control of time and exercise intensity is conducive to the protection of the knee joints.
I hope my answer can help you.