Sarcopenia, characterized by the progressive loss of muscle mass and strength in older adults, is a key factor in health deterioration. It affects 15% of people between 65 and 80 years old and over 50% of those over 80, compromising autonomy and increasing the risk of diseases. Sarcopenia not only impacts muscle function but also bone health, mobility, and is associated with cardiometabolic diseases and cognitive decline. It has been proposed that changes in the gut microbiota in aging individuals, known as gut dysbiosis, contribute to sarcopenia. Species diversity decreases, and bacterial representation is altered, which could impair muscle function through various pathways, such as mitochondrial dysfunction, chronic inflammation, and disruption of protein synthesis. Muscle function loss is strongly associated with cognitive and metabolic impairment in older adults. Recently, it has been demonstrated that fecal microbiota transplantation (FMT) is an effective procedure for modulating gut microbiota and has proven highly effective in managing cases of Clostridium difficile-associated chronic diarrhea. The main objective of this project is to carry out FMT from young, physically active donors to a cohort of older adults to evaluate its effect on muscle, cognitive, and metabolic function. Why donors who exercise? There is growing evidence that gut microbiota diversity is increased in young, physically active individuals. The FMT is planned to be administered through lyophilized microbiota capsules. By restoring microbial diversity, it is expected to improve the quality and function of skeletal muscles, leading to greater cognitive and metabolic resilience. This project has great potential to develop an innovative approach for treating highly debilitating diseases that affect older adults, based on the lyophilization and encapsulation of gut microbiota from young, trained donors, which can be easily stored in a conventional freezer. Due to the high percentage of older adults worldwide and the high prevalence of sarcopenia within this age group, the aim of the project is to address a significant public health issue with a large target population eager for options to promote muscle health, functional autonomy, as well as cognitive and metabolic well-being.