In 2050, ageing population will reach 35% of European population, within it, 30% will suffer sarcopenia. Sarcopenia is recognized as an hallmark of undernutrition in adults. Nutritional enrichment with proteins and exercise limit sarcopenia, but these strategies are difficult to applicate to frail people because of their loss of appetite, non-compliance for exercise or disability. Based on the existence of a gut-muscle axis and the role of microbiota in supplying energy to host (1), the aim of the study is to isolate a probiotic strain that could protect muscle mass for frail individual. We have used fecal sample of one patient with a short bowel syndrome (SBS) as a source of new strains. This patient has had an extensive surgery shortening his gut length and deeply modifying its intestinal microbiota. Since the gut microbiota of SBS is efficient to rescue energy and is very rich in Lactibacillacea, we isolated lactic acid strains from their faeces(2, 3).. The neamatode Caenorhabditis elegans model was used to select a strain able to protect muscle integrity. Lacticaseibacillus casei CNCM-I5663 strain promotes longevity and maintains the mitochondrial networks of wall muscles in C. elegans. Then, this strain was tested in vivo with aged rastephats (18 months) under moderate caloric restriction (75% of ad libitum), mimicking frail individuals. This strain improves insulin sensitivity (HOMA-IR after 2 months of supplementation with probiotic, ANOVA, p=0.056) and preserves the mass of the rats' hindlimb muscles by 12% compared to the restricted controls (ANOVA, p<0.05)(4). The strain Lacticaseibacillus casei CNCM-I5663 strain could be a promising probiotic to limit sarcopenia in specific population, like undernourished older people.