The age-associated decline in muscle mass, also known as sarcopenia, represents a prominent public health problem. Sarcopenia has been associated with functional impairment, progressive disability, increased susceptibility to falls and general slowness of movement, making elderly more dependent on others in daily life. Therefore, the development of effective strategies to prevent sarcopenia constitutes an urgent scientific challenge. Exercise programs can positively affect muscle mass. However, the optimal type, intensity, frequency and duration of exercise to enhance muscle mass is still unknown, especially in elderly. This is partly because the exact loading produced by diverse types of exercises on muscle is not known together with a lack of well-designed long-term clinical trials. Therefore, the main aim of the present project is to obtain fundamental and clinical data to optimize exercise programs stimulating muscle in elderly subjects. The first objective is to measure and model muscle loading during both resistance training exercises as well as impact exercises. These results combined with the results of a parallel project quantifying the loading on femoral neck during the same exercises, will lead us to the second and main objective of the current project. The second objective is to design a novel optimized training program with selected exercises that sufficiently stimulate the target tissues (not only muscle mass but also bone) and to assess the clinical implications of this training protocol, based on a one-year randomized controlled trial in a population of community dwelling elderly above 65 years of age.