The debilitating effects of immobilisation on muscle strength and size in young individuals are well documented. Moreover, sarcopenia has long been recognized as a major cause of muscle strength loss in old age, however, changes in muscle mass and architecture with immobilisation in the elderly has not previously been investigated. This is contrasted by the fact that the elderly population more often undergoes periods of immobilization and disuse not only due to joint pain but also due to a higher degree of co morbidity and hospitalisation.The purpose of the present study was to compare the effect of a 2 week period of unilateral immobilisation on the physiological muscle cross sectional area, maximal isometric muscle strength, specific force, muscle fascicle length and muscle fibre pennation angle in young and old healthy men.