Representative safranin O-fast green-stained histologic sections. (a) Normal articular cartilage from female swim control. Single-headed arrow shows chondrocytes clones. Double-headed arrow demonstrates subchondral bone thickness. (b) Male swim 1.0 DES limb; note abundant chondrocyte clones (single-headed arrow) and fibrillation (arrowhead). (c) Male swim, 1.0 DES. Note paucity of staining, chondrocytes proliferation, and duplication of tide mark (white arrowhead).