In the gym, running on the treadmill is slightly less harmful to the knees than in the open air because of the buffering effect of the treadmill.

But rotation is slightly weaker than running, because the way of running is different. Running is the whole weight of the body pressing on the knees, but the rotation has a seat, so the pressure on the knees is not so great in a certain period of time (although the rotation also has the state of standing and riding).

Generally speaking, both of them will not be too serious when they are fully warmed up and rested after exercise. But for people with knee injuries or middle-aged and elderly athletes, it's best to walk fast or swim.