The present study aims at better understanding the mechanisms of skeletal muscle loss associated with aging. Using muscle biopsies from young and old subjects, the differential expression profiles of mRNA will be obtained through chips that will evaluate more than 39000 transcripts. On the same samples, proteomic analyses will involve two complementary approaches: (1) bidimensional electrophoresis (2DGE) coupled to mass spectrometry (MALDI-ToF) for dominant proteins; (2) Western-blot (more than 800 antibodies) targeting regulating proteins not detectable using 2DGE. Complementary histological studies (immunohisto-fluorescence, confocal microscopy) will specify the localisation of the major biomarkers in the muscle biopsies.