The biopsies are examined histologically for individual muscle fiber size and type (ATPase staining) as well as connective tissue and muscle structure (immunohistological examination collagen I, III and IV, laminin, desmin, tenascin-C). A section of the biopsy is used for mRNA expression by RT-PCR of COL1, COL3 and Tenascin-C. The content of collagen and both enzymatic and non-enzymatic cross-links (HP, LP and pentosidine) are determined by HPLC.