The proximal part of the Achilles tendon was analyzed by TEM imaging in control mice (CTRL, n=24) and transgenic mice with chronic low (GHR−/−, n=15) or high GH/IGF-I activity (bGH, n=15). The images were analyzed for collagen volume fraction (A), collagen fibrils per area (B) and mean collagen fibril diameter (C). Values are mean ± SEM (*p<0.05; ***p<0.001, only differences compared to control are shown).