Inclusion Criteria:  Age ≥ 65 years SARC-F ≥4 or handgrip strength <16 kg for women and < 27 kg for men. Not being afflicted by any condition preventing physical activity. Not being engaged in regular physical activity >20 minutes and >3 days/week. Being able to communicate without difficulty. Being able to read and understand the informed consent form as well as the goals of the study.  Exclusion Criteria:  Acute or terminal illness. Unstable cardiovascular conditions. Conditions or medical treatments affecting the normal production of saliva (i.e. autoimmune disorders such as Sjögren's syndrome or medications like anxiolytics or antidepressants). Being or having been medicated with antibiotics up to one month prior to the taking of samples. Alcohol abuse or regular drug abuse. Severe visual or auditory impairment. Being involved in a different research group with the potential to interfere in our results.