In an effort to better understand the effects of exercise on inflammatory-erosive arthritis in animals, investigators utilized voluntary wheel running and showed it to be sufficient to exacerbate surface erosions localized to entheses as opposed to articular surfaces in both acute (collagen-induced arthritis (CIA)) [13, 14] and chronic (tumor necrosis factor with AU-rich element deletion for systemic overexpression (TNFΔARE)) [15] murine models of RA [16]. Here, TNF is linked to rheumatoid arthritis.