Generally the joints are damaged by high impact activity. The damage is dependent on a lot of factors but generally running is more harmful to joints than for example cycling, especially for heavyier people. Low impact is relatively harmless on joints so cycling, stepping, cross trainer etc are all good. Short term effects are minimal, as are long term for low impact activities. Long term though high impact activiteis, running etc will damage hips, knees, ankles etc. Top runners tend to be very fit and very light they can get away with it for longer.