Some forms of fatigue are obvious: the horse moves slowly, hangs his head, and seems to be struggling to work at the usual level. There is a form of fatigue that might be more difficult to recognize: If the structure of the horse is stressed repeatedly, without enough rest in between, the structure can collapse. The horse might be just fine with a certain level of stress once. But the same stress experienced over and over can cause failure. Fatigue failure of this type is a major factor in the development of arthrosis, a degenerative joint disease. If cartilage in a joint can withstand one day of stress, damage is done when repeated too often.