although moderate intermittent is required to remove matabolic waste meterial from the cartilage the effect produce by heavier compression or by impact loading are somewhat unclear .on the one hand a group of long-distance cross-country runner showed no increaase of pain or other symptoms associated with joint degeneration when compared with a matened group of long-distance swimmer .however a recently published study of histologic change in the knee cartilage of experimantal animals following a treadmill running program showed evidence to gross surface changes were visible to the naked eye and no undue narrowing of the joint space could be detected.